PROJECTS
30 PROJECTS
USING PICBASIC AND
PICBASIC PRO
DOGAN IBRAHIM
Nuwnin
PIC BASIC Projects
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PIC BASIC Projects
30 Projects Using PIC BASIC and
PIC BASIC PRO
By
Dogan Ibrahim
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Contents
Preface ix
1
1
2
5
6
6
6
6
6
7
7
7
7
8
8
8
8
9
9
9
10
10
10
10
10
10
11
11
11
The PIC microcontroller family 13
2.1 12-bit instruction word 15
2.2 14-bit instruction word 17
2.3 16-bit instruction word 21
2.4 Inside a PIC microcontroller 21
2.4.1 Program memory (Flash) 21
2.4.2 Data memory (RAM) 22
1 Microcontroller systems
1.1
Introduction
1.2
Microcontroller systems
1.2.1
RAM
1.2.2
ROM
1.2.3
EPROM
1.2.4
EEPROM
1.2.5
Flash EEPROM
1.3
Microcontroller features
1.3.1
Supply voltage
1.3.2
The clock
1.3.3
Timers
1.3.4
Watchdog
1.3.5
Reset input
1.3.6
Interrupts
1.3.7
Brown-out detector
1.3.8
Analogue-to-digital converter
1.3.9
Serial I/O
1.3.10
EEPROM data memory
1.3.11
LCD drivers
1.3.12
Analogue comparator
1.3.13
Real-time clock
1.3.14
Sleep mode
1.3.15
Power-on reset
1.3.16
Low power operation
1.3.17
Current sink/source capability
1.4
Microcontroller architectures
1.4.1
RISC and CISC
1.5
Exercises
vi Contents
2 A3 Register file map and special function registers 22
2.4.4 Oscillator circuits 34
2.4.5 Reset circuit 40
2.4.6 Interrupts 41
2.4.7 The configuration word 42
2.4.8 I/O interface 42
2.5 Exercises 47
PIC microcontroller project development 49
3.1 Required hardware tools 49
3.1.1 PC 49
3.1.2 PIC microcontroller programmer device 50
3.1.3 Solderless breadboard 52
3.1.4 PIC microcontroller and minimum support components 53
3.1.5 Power supply 58
3.2 Required software tools 60
3.2.1 Text editor 60
3.2.2 PicBasic and PicBasic Pro compilers 65
3.2.3 Programmer device software 67
3.3 Bundled development systems 69
3.4 Experimenter boards 71
3.5 Example project development 73
3.6 Other useful development tools 77
3.6.1 Simulators 77
3.6.2 In Circuit Emulators (ICE) 77
3.7 Exercises 78
3.8 Links to useful web sites 78
PicBasic and PicBasic Pro programming 80
4.1 PicBasic language 80
4.1.1 PicBasic variables 80
4.1.2 PicBasic mathematical and logical operations 85
4.1.3 PicBasic program flow control commands 86
4.1.4 Other PicBasic commands 90
4.1.5 Recommended PicBasic program structure 101
4.2 PicBasic Pro language 101
4.2.1 PicBasic Pro variables 102
4.2.2 Constants 103
4.2.3 Comments 103
4.2.4 Multi-statement lines 103
4.2.5 INCLUDE 104
4.2.6 DEFINE 104
4.2.7 Line extension 104
4.2.8 Accessing ports and other registers in PicBasic Pro 104
Contents vii
4.3
4.4
4.5
4.6
4.7
4.8
4.2.9 Arithmetic operators
4.2.10 PicBasic Pro commands
Liquid crystal display (LCD) interface and commands
4.3.1 Parallel LCDs
4.3.2 Serial LCDs
Interrupts
Recommended PicBasic Pro program structure
Using stepping motors
Using servomotors
Exercises
5 PicBasic and PicBasic Pro projects
Project 1 - Simple flashing LED
Project 2 - Complex flashing LED
Project 3 - Flashing LED warning lights
Project 4 - Turning on odd numbered LEDs
Project 5 - Binary counting LEDs
Project 6 - Left scrolling LEDs
Project 7 - Right scrolling LEDs
Project 8 - Right-left scrolling LEDs
Project 9 - LED dice
Project 10 - 7-segment LED display counter
Project 1 1 - 7-segment LED dice
Project 12 - Dual 7-segment LED display
Project 13 - Dual 7-segment LED display counter
Project 14 - Dual 7-segment LED event counter
Project 15 - 4-digit display with serial driver - counter project
Project 16 - 4-digit LED with serial driver - counter project with leading zeroes blanked
Project 17 - 4-digit external interrupt-driven event counter
Project 1 8 - 4-digit timer interrupt-driven chronograph
Project 19 - Car park control system
Project 20 - Seconds counter with LCD display
Project 2 1 - LCD-based clock with hours-minutes-seconds display
Project 22 - LCD-based chronometer
Project 23 - LCD-based voltmeter using A/D converter
Project 24 - LCD-based thermometer using A/D converter
Project 25 - Serial LCD-based thermometer with external EEPROM memory
Project 26 - Programmable thermometer with RS232 serial output
Project 27 - Electronic organ
Project 28 - Unipolar stepping motor control
Project 29 - Unipolar stepping motor control using UCN5804B
Project 30 - Servomotor-based mobile robot control
About the CDROM
Index
105
107
113
114
120
124
125
126
128
129
131
132
138
142
144
148
152
156
160
165
172
182
189
198
204
210
227
236
241
248
260
271
280
288
300
306
315
331
337
344
348
359
361
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Preface
Microcontrollers are single-chip computers consisting of CPU (central processing unit), data and
program memory, serial and parallel I/O (input/output), timers, external and internal interrupts,
all integrated into a single chip that can be purchased for as little as $2.00. Microcontrollers are
intelligent electronic devices used to control and monitor devices in the real world. Today micro-
controllers are used in most commercial and industrial equipment. About 40% of microcontroller
applications are in office automation, such as PCs, laser printers, fax machines, intelligent tele-
phones, and so forth. About one- third of microcontrollers are found in consumer electronics
goods. Products such as CD players, hi-f- equipment, video games, washing machines and cook-
ers fall into this category. The communications market, automotive market, and the military share
the rest of the application areas.
Microcontrollers are programmed devices. A program is a sequence of instructions that tell the
microcontroller what to do. Microcontrollers have traditionally been programmed using the low-
level assembly language of the target processor. This consists of a series of instructions in the
form of mnemonics. The biggest disadvantage of assembly language is that microcontrollers from
different manufacturers have different assembly languages and the user is forced to learn a new
language every time a new processor is chosen. Assembly language is also difficult to work with,
especially during the development, testing, and maintenance of complex projects. The solution to
this problem has been to use a high-level language to program microcontrollers. A high-level lan-
guage consists of easy to understand, more meaningful series of instructions. This approach makes
the programs more readable and also portable. The same high-level language can usually be used
to program different types of microcontrollers. Testing and the maintenance of microcontroller-based
projects are also easier when high-level languages are used.
This book is about programming microcontrollers using a high-level language. The PIC family of
microcontrollers is chosen as the target microcontroller. PIC is currently one of the most popular
microcontrollers used by many engineers, technicians, students, and hobbyists. PIC microcon-
trollers are manufactured in different sizes and in varying complexity. These microcontrollers
incorporate a RISC (reduced instruction set computer) architecture and there is only a small set
of instructions that the user has to learn. Also, the power consumption of PIC microcontrollers is
very low and this is one of the reasons which make these microcontrollers popular in portable
hand-held applications.
In this book, PicBasic and PicBasic Pro languages are used to program PIC microcontrollers.
BASIC is one of the oldest and widely known high-level programming languages. Both PicBasic
and PicBasic Pro have been developed by MicroEngineering Labs Inc. PicBasic is a low-cost com-
piler and is aimed at the lower end of the market, mainly for students and the hobby market.
x Preface
PicBasic Pro is more expensive and it is a sophisticated professional compiler with many extra fea-
tures. This compiler is aimed for engineers and other professional users of PIC microcontrollers.
This book will help technicians, engineers, and to those who chose electronics as a hobby. No previ-
ous experience with microcontrollers is assumed, and the PIC family of microcontrollers is intro-
duced in detail. The book is practical and is supplied with many working hardware projects where the
reader can experiment easily using a simple breadboard type experiment kit and a few components.
The circuit diagram, flow diagram, and the code for each project are given and explained in detail.
Chapter 1 provides a review of the basic architecture of microcontrollers. Various microcontroller
concepts are described in this chapter.
Chapter 2 is about the common features of PIC microcontrollers and describes in detail the archi-
tecture of various types of commonly used PIC microcontrollers and their use in electronic devices.
A microcontroller-based system development requires both hardware and software development
tools. Chapter 3 describes the various commercially available PIC microcontroller development
tools and gives a brief overview of how they can be used in project development.
PicBasic and PicBasic Pro languages are discussed in detail in Chapter 4. A brief description of
each statement is given with an example.
Finally, in Chapter 5, many tested and working projects are given. These projects are organized in
increasing complexity and the reader is recommended to follow this chapter in the given order.
Dogan Ibrahim
1
Microcontroller systems
1.1 Introduction
In 1969, Bob Noyce and Gordon Moore set up the Intel Corporation to manufacture memory chips
for the mainframe computer industry. Later in 1971, the first microprocessor chip 4040 was manu-
factured by Intel for a consortium of two Japanese companies. These chips were basically designed
for a calculator named Busicom which was one of the first portable calculators. This was a very
simple calculator which could only add and subtract numbers, 4 bits (a nibble) at a time. 4040
chip was so successful that it was soon followed by Intel's 8-bit 8008 microprocessor. This was a
simple microprocessor with limited resources, poorly implemented interrupt mechanisms, and
multiplexed address and data busses. The first really powerful 8-bit microprocessor appeared in early
1974 as the Intel 8080 chip. This microprocessor had separate address and data busses with 64 K
byte of address space which was enormous in 1975 standards. 8080 microprocessor was the first
microprocessor used in homes as a personal computer named Altair. 8080 has been a very success-
ful microprocessor but soon other companies began producing microprocessor chips. Motorola
introduced the 8-bit 6800 chip which had a different architecture to the 8080 but has also been very
popular. In 1976, Zilog introduced the Z80 microprocessor which was much more advanced than the
8080. The instruction set of Z80 was downward compatible with the 8080 and this made Z80 to be
one of the most successful microprocessors of the time. Z80 was used in many microprocessor-
based applications, including home computers and games consoles. In 1976, Motorola created a
microprocessor chip called 6801 which replaced a 6800 chip plus some of the chips required to
make a complete computer system. This was a major step in the evolution of the microcontrollers
which are basically computers consisting of only one chip. In later years, we see many other micro-
controller chips in the market, such as Intel 8048, 8049, 8051, Motorola 6809, Atmel 89C51, etc.
The term microcomputer is used to describe a system that includes a minimum of a microprocessor,
program memory, data memory, and input-output (I/O). Some microcomputer systems include
additional components such as timers, counters, analogue-to-digital converters, and so on. Thus,
a microcomputer system can be anything from a large computer having hard disks, floppy disks,
and printers, to a single-chip embedded controller.
In this book we are going to consider only the type of microcomputers that consists of a single sil-
icon chip. Such microcomputer systems are also called microcontrollers and they are used in
many household goods such as microwave ovens, TV remote control units, cookers, hi-fi equip-
ment, CD players, personal computers, fridges, etc.
2 PIC BASIC projects
1 .2 Microcontroller systems
A microcontroller is a single chip computer (see Figure 1.1). Micro suggests that the device is
small, and controller suggests that the device can be used in control applications. Another term
used for microcontrollers is embedded controller, since most of the microcontrollers are built into
(or embedded in) the devices they control.
A microprocessor differs from a microcontroller in many ways. The main difference is that a micro-
processor requires several other components for its operation, such as program memory and data
memory, I/O devices, and external clock circuit. A microcontroller on the other hand has all the sup-
port chips incorporated inside the same chip. All microcontrollers operate on a set of instructions (or
the user program) stored in their memory. A microcontroller fetches the instructions from its pro-
gram memory one by one, decodes these instructions, and then carries out the required operations.
Microcontrollers have traditionally been programmed using the assembly language of the target
device. Although the assembly language is fast, it has several disadvantages. An assembly pro-
gram consists of mnemonics and it is difficult to learn and maintain a program written using the
assembly language. Also, microcontrollers manufactured by different firms have different assem-
bly languages and the user is required to learn a new language every time a new microcontroller
is used. Microcontrollers can also be programmed using a high-level language, such as BASIC,
PASCAL, and C. High-level languages have the advantage that it is much easier to learn a high-
level language than the assembler. Also, very large and complex programs can easily be developed
using a high-level language. In this book we shall be learning the programming of PIC micro-
controllers using the popular PicBasic and PicBasic Pro compilers.
In general, a single chip is all that is required to have a running microcontroller system. In prac-
tical applications additional components may be required to allow a microcomputer to interface
to its environment. With the advent of the PIC family of microcontrollers the development time
of an electronic project has reduced to several hours. Developing a PIC microcontroller-based
project simply takes no more than five or six steps.
1 . Type the program into a PC
2. Assemble (or compile) the program
3. Optionally simulate the program on a PC
4. Load the program into PIC's program memory
5. Design and construct the hardware
6. Test the project.
Basically, a microcomputer executes a user program which is loaded in its program memory. Under
the control of this program data is received from external devices (inputs), manipulated and then
sent to external devices (outputs). For example, in a microcontroller-based oven temperature con-
trol system the temperature is read by the microcomputer using a temperature sensor. The micro-
computer then operates a heater or a fan to control and keep the temperature at the required value.
Figure 1.2 shows the block diagram of our simple oven temperature control system.
Microcontroller systems 3
Figure 1.1 Some PIC microcontrollers
Microcontroller
Oven
Figure 1.2 Microcontroller-based oven temperature control system
The system shown in Figure 1 .2 is a very simplified temperature control system. In a more sophis-
ticated system we may have a keypad to set the temperature, and a liquid crystal display (LCD) to
display the current temperature. Figure 1.3 shows the block diagram of this more sophisticated
temperature control system.
We can make our design even more sophisticated (see Figure 1.4) by adding an audible alarm to
inform us if the temperature is outside the required values. Also, the temperature readings can be
sent to a PC every second for archiving and further processing. For example, a graph of the daily
temperature can be plotted on the PC. As you can see, because the microcontrollers are program-
mable it is very easy to make the final system as simple or as complicated as we like.
4 PIC BASIC projects
LCD
Output
Output
Output
Inputs
Microcontroller
Oven
Heater
Fan
X
Sensor
□ □ □
□ □ □
□ □ □
Keypad
Figure 1.3 Temperature control system with a keypad and LCD
A microcontroller is a very powerful tool that allows a designer to create sophisticated I/O data
manipulation under program control. Microcontrollers are classified by the number of bits they
process. 8-bit microcontrollers are the most popular ones and are used in most microcontroller-
based applications; 16- and 32-bit microcontrollers are much more powerful, but usually more
expensive and not required in many small- to medium-size general-purpose applications where
microcontrollers are generally used.
As shown in Figure 1.5, the simplest microcontroller architecture consists of a microprocessor,
memory, and I/O. The microprocessor consists of a central processing unit (CPU) and the control
unit (CU). The CPU is the brain of the microcontroller and this is where all of the arithmetic and
logic operations are performed. The CU controls the internal operations of the microprocessor and
sends out control signals to other parts of the microcontroller to carry out the required instructions.
Memory is an important part of a microcontroller system. Depending upon the type used we can
classify memories into two groups: program memory and data memory. Program memory stores
the program written by the programmer and this memory is usually non-volatile, i.e. data is not
lost after the removal of power. Data memory is where the temporary data used in a program are
stored and this memory is usually volatile, i.e. data is lost after the removal of power.
There are basically five types of memories as summarised below.
Microcontroller systems 5
LCD
Microcontroller
Output
Output
Output
Output
Input
Input Output
— i —
□ □ □
□ □ □
□ □ □
Oven
Heater
Fan
Buzzer
Sensor
PC
Keypad
Figure 1.4 More sophisticated temperature controller
► External devices
Figure 1.5 The simplest microcontroller architecture
1.2. 1 RAM
RAM means Random Access Memory. It is a general-purpose memory which usually stores the
user data used in a program. RAM is volatile, i.e. data is lost after the removal of power. Most
microcontrollers have some amount of internal RAM. 256 bytes is a common amount, although
some microcontrollers have more, some less. In general it is possible to extend the memory by
adding external memory chips.
6 PIC BASIC projects
1.2.2 ROM
ROM is Read Only Memory. This type of memory usually holds program or fixed user data. ROM
memories are programmed at factory during the manufacturing process and their contents cannot
be changed by the user. ROM memories are only useful if you have developed a program and wish
to order several thousand copies of it.
1.2.3 EPROM
EPROM is erasable Programmable Read Only Memory. This is similar to ROM, but the EPROM
can be programmed using a suitable programming device. EPROM memories have a small clear
glass window on top of the chip where the data can be erased under UV light. Many development
versions of microcontrollers are manufactured with EPROM memories where the user program
can be stored. These memories are erased and re-programmed until the user is satisfied with the
program. Some versions of EPROMs, known as OTP (One Time Programmable), can be pro-
grammed using a suitable programmer device but these memories cannot be erased. OTP mem-
ories cost much less than the EPROMs. OTP is useful after a project has been developed
completely and it is required to make many copies of the program memory.
1.2.4 EEPROM
EEPROM is Electrically Erasable Programmable Read Only Memory, which is a non- volatile mem-
ory. These memories can be erased and also be programmed under program control. EEPROMs are
used to save configuration information, maximum and minimum values, identification data, etc.
Some microcontrollers have built-in EEPROM memories (e.g. PIC16F84 contains a 64-byte EEP-
ROM memory where each byte can be programmed and erased directly by software). EEPROM
memories are usually very slow.
1.2.5 Flash EEPROM
This is another version of EEPROM-type memory. This memory has become popular in micro-
controller applications and is used to store the user program. Flash EEPROM is non- volatile and
is usually very fast. The data is erased and then re-programmed using a programming device. The
entire contents of the memory should be erased and then re-programmed.
1 .3 Microcontroller features
Microcontrollers from different manufacturers have different architectures and different capa-
bilities. Some may suit a particular application while others may be totally unsuitable for the same
application. The hardware features of microcontrollers in general are described in this section.
Microcontroller systems 7
1.3.1 Supply voltage
Most microcontrollers operate with the standard logic voltage of +5 V. Some microcontrollers
can operate at as low as +2.7 V and some will tolerate +6 V without any problems. You should
check the manufacturers' data sheets about the allowed limits of the power supply voltage.
A voltage regulator circuit is usually used to obtain the required power supply voltage when the
device is to be operated from a mains adaptor or batteries. For example, a 5 V regulator is required
if the microcontroller is to be operated from a 5 V supply using a 9 V battery.
1.3.2 The clock
All microcontrollers require a clock (or an oscillator) to operate. The clock is usually provided by
connecting external timing devices to the microcontroller. Most microcontrollers will generate clock
signals when a crystal and two small capacitors are connected. Some will operate with resonators or
external resistor-capacitor pair. Some microcontrollers have built-in timing circuits and they do not
require any external timing components. If your application is not time- sensitive you should use
external or internal (if available) resistor-capacitor timing components for simplicity and low cost.
An instruction is executed by fetching it from the memory and then decoding it. This usually takes
several clock cycles and is known as the instruction cycle. In PIC microcontrollers an instruction
cycle takes four-clock periods. Thus, the microcontroller is actually operated at a clock rate which
is a quarter of the actual oscillator frequency.
1.3.3 Timers
Timers are important parts of any microcontroller. A timer is basically a counter which is driven
either from an external clock pulse or from the internal oscillator of the microcontroller. A timer
can be 8-bits or 16-bits wide. Data can be loaded into a timer under program control and the timer
can be stopped or started by program control. Most timers can be configured to generate an inter-
rupt when they reach a certain count (usually when they overflow). The interrupt can be used by
the user program to carry out accurate-timing-related operations inside the microcontroller.
Some microcontrollers offer capture and compare facilities where a timer value can be read when
an external event occurs, or the timer value can be compared to a preset value and an interrupt can
be generated when this value is reached.
It is typical to have at least one timer in every microcontroller. Some microcontrollers may have
two, three, or even more timers where some of the timers can be cascaded for longer counts.
1.3.4 Watchdog
Most microcontrollers have at least one watchdog facility. The watchdog is basically a timer which
is refreshed by the user program and a reset occurs if the program fails to refresh the watchdog. The
8 PIC BASIC projects
watchdog timer is used to detect a system problem, such as the program being in an endless loop.
A watchdog is a safety feature that prevents runaway software and stops the microcontroller from
executing meaningless and unwanted code. Watchdog facilities are commonly used in real-time
systems where it is required to regularly check the successful termination of one or more activities.
1.3.5 Reset input
A reset input is used to reset a microcontroller. Resetting puts the microcontroller into a known
state such that the program execution starts from address of the program memory. An external
reset action is usually achieved by connecting a push-button switch to the reset input such that the
microcontroller can be reset when the switch is pressed.
1.3.6 Interrupts
Interrupts are very important concepts in microcontrollers. An interrupt causes the microcon-
troller to respond to external and internal (e.g. a timer) events very quickly. When an interrupt
occurs the microcontroller leaves its normal flow of program execution and jumps to a special
part of the program, known as the Interrupt Service Routine (ISR). The program code inside the
ISR is executed and upon return from the ISR the program resumes its normal flow of execution.
The ISR starts from a fixed address of the program memory. This address is also known as the
interrupt vector address. For example, in a PIC16F84 microcontroller the ISR starting address is
4 in the program memory. Some microcontrollers with multi-interrupt features have just one
interrupt vector address, while some others have unique interrupt vector addresses, one for each
interrupt source. Interrupts can be nested such that a new interrupt can suspend the execution of
another interrupt. Another important feature of a microcontroller with multi-interrupt capability
is that different interrupt sources can be given different levels of priority.
1.3.7 Brown-out detector
Brown-out detectors are also common in many microcontrollers and they reset a microcontroller
if the supply voltage falls below a nominal value. Brown-out detectors are safety features and they
can be employed to prevent unpredictable operation at low voltages, especially to protect the con-
tents of EEPROM-type memories.
1.3.8 Analogue-to-digital converter
An analogue-to-digital converter (A/D) is used to convert an analogue signal such as voltage to a
digital form so that it can be read by a microcontroller. Some microcontrollers have built-in A/D
converters. It is also possible to connect an external A/D converter to any type of microcontroller.
A/D converters are usually 8-bits, having 256 quantisation levels. Some microcontrollers have
10-bit A/D converters with 1024 quantisation levels. Most PIC microcontrollers with A/D features
have multiplexed A/D converters where more than one analogue input channel is provided.
Microcontroller systems 9
The A/D conversion process must be started by the user program and it may take several hundreds
of microseconds for a conversion to complete. A/D converters usually generate interrupts when a
conversion is complete so that the user program can read the converted data quickly.
A/D converters are very useful in control and monitoring applications since most sensors (e.g.
temperature sensor, pressure sensor, force sensor, etc.) produce analogue output voltages.
1.3.9 Serial I/O
Serial communication (also called RS232 communication) enables a microcontroller to be con-
nected to another microcontroller or to a PC using a serial cable. Some microcontrollers have
built-in hardware called US ART (Universal Synchronous-Asynchronous Receiver-Transmitter)
to implement a serial communication interface. The baud rate and the data format can usually be
selected by the user program. If any serial I/O hardware is not provided, it is easy to develop soft-
ware to implement serial data communication using any I/O pin of a microcontroller. We shall see
in Chapter 4 how to use the PicBasic and PicBasic Pro statements to send and receive serial data
from any pin of a PIC microcontroller.
Some microcontrollers incorporate SPI (Serial Peripheral Interface) or I 2 C (Integrated Inter
Connect) hardware bus interfaces. These enable a microcontroller to interface to other compatible
devices easily.
1.3. 10 EEPROM data memory
EEPROM type data memory is also very common in many microcontrollers. The advantage of an
EEPROM memory is that the programmer can store non- volatile data in such a memory, and can
also change this data whenever required. For example, in a temperature monitoring application
the maximum and the minimum temperature readings can be stored in an EEPROM memory.
Then, if the power supply is removed for whatever reason, the values of the latest readings will
still be available in the EEPROM memory.
PicBasic and PicBasic Pro languages provide special instructions for reading and writing to the
EEPROM memory of a microcontroller which has such memory built-in.
Some microcontrollers have no built-in EEPROM memory, some provide only 16 bytes of
EEPROM memory, while some others may have as much as 256 bytes of EEPROM memories.
1.3.11 LCD drivers
LCD drivers enable a microcontroller to be connected to an external LCD display directly.
These drivers are not common since most of the functions provided by them can be implemented
in software.
10 PIC BASIC projects
1.3.12 Analogue comparator
Analogue comparators are used where it is required to compare two analogue voltages. Although
these circuits are implemented in most high-end PIC microcontrollers they are not common in
other microcontrollers.
1.3.13 Real-time clock
Real-time clock enables a microcontroller to have absolute date and time information continu-
ously. Built-in real-time clocks are not common in most microcontrollers since they can easily be
implemented by either using a dedicated real-time clock chip, or by writing a program.
1.3.14 Sleep mode
Some microcontrollers (e.g. PIC) offer built-in sleep modes where executing this instruction puts
the microcontroller into a mode where the internal oscillator is stopped and the power consump-
tion is reduced to an extremely low level. The main reason of using the sleep mode is to conserve
the battery power when the microcontroller is not doing anything useful. The microcontroller usu-
ally wakes up from the sleep mode by external reset or by a watchdog time-out.
1.3.15 Power-on reset
Some microcontrollers (e.g. PIC) have built-in power-on reset circuits which keep the microcon-
troller in reset state until all the internal circuitry has been initialised. This feature is very useful
as it starts the microcontroller from a known state on power-up. An external reset can also be pro-
vided where the microcontroller can be reset when an external button is pressed.
1.3.16 Low power operation
Low power operation is especially important in portable applications where the microcontroller-
based equipment is operated from batteries. Some microcontrollers (e.g. PIC) can operate with
less than 2 mA with 5 V supply, and around 15 |xA at 3 V supply. Some other microcontrollers,
especially microprocessor-based systems where there could be several chips may consume sev-
eral hundred milliamperes or even more.
1.3.17 Current sink/source capability
This is important if the microcontroller is to be connected to an external device which may draw
large current for its operation. PIC microcontrollers can source and sink 25 mA of current from
each output port pin. This current is usually sufficient to drive LEDs, small lamps, buzzers, small
relays, etc. The current capability can be increased by connecting external transistor switching
circuits or relays to the output port pins.
Microcontroller systems 1 1
1 .4 Microcontroller architectures
Usually two types of architectures are used in microcontrollers (see Figure 1.6): Von Neumann
architecture and Harvard architecture. Von Neumann architecture is used by a large percentage of
microcontrollers and here all memory space is on the same bus and instruction and data use the
same bus. In the Harvard architecture (used by the PIC microcontrollers), code and data are on
separate busses and this allows the code and data to be fetched simultaneously, resulting in an
improved performance.
< — ►
Program
memory
< — ►
Program
memory
CPU
CPU
Data
memory
< — ►
Figure 1.6 Von Neumann and Harvard architectures
1.4.1 RISC and CISC
RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Computer) refer to
the instruction set of a microcontroller. In an 8-bit RISC microcontroller, data is 8-bits wide but
the instruction words are more than 8-bits wide (usually 12, 14, or 16-bits) and the instructions
occupy one word in the program memory. Thus, the instructions are fetched and executed in one
cycle, resulting in an improved performance. PIC microcontrollers are RISC-based devices and
they have no more than 35 instructions.
In a CISC microcontroller both data and instructions are 8-bits wide. CISC microcontrollers usually
have over 200 instructions. Data and code are on the same bus and cannot be fetched simultaneously.
1 .5 Exercises
1 . What is a microcontroller? What is a microprocessor? Explain the main differences between
a microprocessor and a microcontroller.
2. Give some example applications of microcontrollers around you.
3. Where would you use an EPROM memory?
4. Where would you use a RAM memory?
5. Explain what type of memories are usually used in microcontrollers.
6. What is an I/O port?
7. What is an analogue-to-digital converter? Give an example use for this converter.
12 PIC BASIC projects
8. Explain why a watchdog timer could be useful in a real-time system.
9. What is serial I/O? Where would you use serial communication?
10. Why is the current sinking/sourcing important in the specification of an output port pin?
1 1 . What is an interrupt? Explain what happens when an interrupt is recognised by a microcontroller.
12. Why is brown-out detection important in real-time systems?
13. Explain the differences between a RISC-based microcontroller and a CISC-based microcon-
troller. What type of microcontroller is PIC?
2
The PIC microcontroller family
The PIC microcontroller family of microcontrollers is manufactured by Microchip Technology
Inc. Currently they are one of the most popular microcontrollers used in many commercial and
industrial applications. Over 120 million devices are sold each year.
The PIC microcontroller architecture is based on a modified Harvard RISC (Reduced Instruction
Set Computer) instruction set with dual-bus architecture, providing fast and flexible design with
an easy migration path from only 6 pins to 80 pins, and from 384 bytes to 128 kbytes of program
memory.
PIC microcontrollers are available with many different specifications depending on:
• Memory Type
- Flash
- OTP (One-time-programmable)
- ROM (Read-only-memory)
- ROMless
• Input-Output (I/O) Pin Count
- 4-18 pins
- 20-28 pins
- 32-44 pins
- 45 and above pins
• Memory Size
- 0.5-1 K
- 2-4 K
- 8-16K
- 24-32 K
- 48-64 K
- 96-128 K
• Special Features
- CAN
- USB
- LCD
- Motor Control
- Radio Frequency
14 PIC BASIC projects
Although there are many models of PIC microcontrollers, the nice thing is that they are upward
compatible with each other and a program developed for one model can very easily, and in many
cases with no modifications, be run on other models of the family. The basic assembler instruction
set of PIC microcontrollers consists of only 33 instructions and most of the family members (except
the newly developed devices) use the same instruction set. This is why a program developed for one
model can run on another model with similar architecture without any changes.
All PIC microcontrollers offer the following features:
• RISC instruction set with only a handful of instructions to learn
• Digital I/O ports
• On-chip timer with 8-bit prescaler
• Power-on reset
• Watchdog timer
• Power saving SLEEP mode
• High source and sink current
• Direct, indirect, and relative addressing modes
• External clock interface
• RAM data memory
• EPROM or Flash program memory
Some devices offer the following additional features:
• Analogue input channels
• Analogue comparators
• Additional timer circuits
• EEPROM data memory
• External and internal interrupts
• Internal oscillator
• Pulse-width modulated (PWM) output
• USART serial interface
Some even more complex devices in the family offer the following additional features:
• CAN bus interface
• I 2 C bus interface
• SPI bus interface
• Direct LCD interface
• USB interface
• Motor control
Although there are several hundred models of PIC microcontrollers, choosing a microcontroller
for an application is not a difficult task and requires taking into account these factors:
• Number of I/O pins required
• Required peripherals (e.g. USART, USB)
The PIC microcontroller family 15
• The minimum size of program memory
• The minimum size of RAM
• Whether or not EEPROM non- volatile data memory is required
• Speed
• Physical size
• Cost.
The important point to remember is that there could be many models which satisfy all of the above
requirements. You should always try to find the model which satisfies your minimum require-
ments and the one which does not offer more than you may need. For example, if you require a
microcontroller with only 8 I/O pins and if there are two identical microcontrollers, one with 8
and the other one with 16 I/O pins, you should select the one with 8 I/O pins.
Although there are several hundred models of PIC microcontrollers, the family can be broken
down into three main groups, which are:
• 12-bit instruction word (e.g. 12C5XX, 16C5X)
• 14-bit instruction word (e.g. 16F8X, 16F87X)
• 16-bit instruction word (e.g. 17C7XX, 18C2XX).
All three groups share the same RISC architecture and the same instruction set, with a few add-
itional instructions available for the 14-bit, and many more instructions available for the 16-bit
models. Instructions occupy only one word in memory, thus increasing the code efficiency and
reducing the required program memory. Instructions and data are transferred on separate buses,
thus the overall system performance is increased.
The features of some microcontrollers in each group are given in the following sections.
2.1 12-bit instruction word
Table 2.1 lists some of the devices in this group. Because of the simplicity of their architecture
these devices are not supported by the PicBasic compiler. PicBasic Pro compiler provides a limited
support for these devices. But, as the prices of 14-bit devices have declined, there really is no need
anymore to use a 12-bit device, except for their smaller physical sizes.
PIC12C508: This is a low-cost, 8-pin device with 512 X 12 EPROM program memory, and 25
bytes of RAM data memory. The device can operate at up to 4 MHz clock input and the instruc-
tion set consists of only 33 instructions. The device features 6 I/O ports, 8-bit timer, power-on
reset, watchdog timer, and internal 4 MHz oscillator capability. One of the major disadvantages of
this microcontroller is that the program memory is EPROM-based and it cannot be erased or pro-
grammed using the standard programming devices. The program memory has to be erased using
an EPROM eraser device (an ultraviolet light source).
The "F" version of this family (e.g. PIC12F508) is based on flash program memory which can be
erased and re-programmed using the standard PIC programmer devices. Similarly, the "CE" version of
the family (e.g. PIC12CE518) offers an additional 16-byte non- volatile EEPROM data memory.
16 PIC BASIC projects
Table 2.1 Some 12-bit PIC microcontrollers
Microcontroller
Program
Memory
Data
RAM
Max speed
(MHz)
I/O
Ports
A/D
Converter
12C508
512 X 12
25
4
6
-
16C54
384 X 12
25
20
12
-
16C57
2048 X 12
72
20
20
-
16C505
1024 X 12
41
4
12
-
16C58A
2048 X 12
73
20
12
-
Figure 2.1 shows the pin configuration of the PIC12F508 microcontroller.
VDD
GP5/OSC1/CLKIN 4
GP4/OSC2 <
GP3/MCLR/VPP
Figure 2.1 PIC12F508 microcontroller
VSS
► GP0/ICSPDAT
► GP1/ICSPCLK
► GP2/T0CKI
PIC16C5X: This is one of the earliest PIC microcontrollers. The device is 18-pin with a 384 X 12
EPROM program memory, 25 bytes of RAM data memory, 12 I/O ports, a timer, and a watchdog.
Some other members in the family, e.g. PIC16C56 have the same architecture but more program
memory (1024 X 12). PIC16C58A has more program memory (2048 X 12) and also more data mem-
ory (73 bytes of RAM). Figure 2.2 shows the pin configuration of the PIC16C56 microcontroller.
RA2«
XJ
RB3 4
5 5 5 5 5 5
o o o o o o
20 > ► RA1
19 >
18
17
16
o <j> a (j> g> O)
O O O O O O . c
TJ Ol TJ cn TJ Ol io
CJ1 00 Ol & & *
00 G> -P^
► RAO
-OSC1/CLKIN
] ► OSC2/CLKOUT
> VDD
> VDD
14 > ► RB7
13 > ► RB6
12 > ► RB5
1 1 ~}* ► RB4
Figure 2.2 PIC16C56 microcontroller
The PIC microcontroller family 17
2.2 14-bit instruction word
This is a big family including many models of PIC microcontrollers. These devices are supported
by both the PicBasic and PicBasic Pro compilers. Most of the devices in this family can operate
at up to 20 MHz clock rate. The instruction set consists of 35 instructions. These devices offer
advanced features such as internal and external interrupt sources. Table 2.2 lists some of the
microcontrollers in this group.
Table 2.2 Some 14-bit microcontrollers
Microcontroller
Program
Memory
Data
RAM
Max speed
(MHz)
I/O
Ports
A/D
Converter
16C554
512 X 14
80
20
13
-
16C64
2048 X 14
128
20
33
-
16F84
1024 X 14
36
10
13
-
16F627
1024 X 14
224
20
16
-
16F628
2048 X 14
224
20
16
-
16F676
1024 X 14
64
20
12
8
16F73
4096 X 14
192
20
22
5
16F876
8192 X 14
368
20
22
5
16F877
8192 X 14
368
20
33
8
PIC16C554: This microcontroller has similar architecture to the PIC16C54 but the instructions
are 14 bits wide. The program memory is 512 X14 and the data memory is 80 bytes of RAM.
There are 1 3 I/O pins where each pin can source or sink 25 mA current. Additionally, the device
contains a timer and a watchdog.
PIC16F84: This has been one of the most popular PIC microcontrollers for a very long time. This
is an 18-pin device and it offers 1024 X 14 flash program memory, 36 bytes of data RAM,
64 bytes of non- volatile EEPROM data memory, 13 I/O pins, a timer, a watchdog, and internal and
external interrupt sources. The timer is 8-bits wide but can be programmed to generate internal
interrupts for timing purposes. PIC16F84 can be operated from a crystal or a resonator for accur-
ate timing. A resistor-capacitor can also be used as a timing device for applications where accur-
ate timing is not required.
We will be using the PIC16F84 in some of the projects in this book. Figure 2.3 shows the pin con-
figuration of this microcontroller. The pin descriptions are given in Table 2.3.
PIC16F877: This microcontroller is a 40-pin device and is one of the popular microcontrollers
used in complex applications. The device offers 8192 X 14 flash program memory, 368 bytes of
RAM, 256 bytes of non-volatile EEPROM memory, 33 I/O pins, 8 multiplexed A/D converters
with 10-bits resolution, PWM generator, 3 timers, analogue capture and comparator circuit,
US ART, and internal and external interrupt facilities.
18 PIC BASIC projects
RA2«
RA4/T0CKI <
> ►RAI
>
>
-► RAO
-OSC1/CLKIN
] ► OSC2/CLKOUT
> VDD
>RB7
>
> ► RBG
]« ► RB5
>
> RB4
Figure 2.3 PIC16F84 microcontroller pin configuration
Table 2.3 PIC 1 6F84 microcontroller pin descriptions
Pin
Description
Pin
Description
1
RA2 - PORTA bit 2
10
RB4 - PORTB bit 4
2
RA3 - PORTA bit 3
11
RB5 - PORTB bit 5
3
RA4/T0CK1 - PORTA bit 4/Counter elk
12
RB6-PORTBbit6
4
MCLR - Master clear
13
RB7 - PORTB bit 7
5
Vss - Gnd
14
Vdd - + V supply
6
RBO/INT-PORTBbitO
15
OSC2
7
RBl-PORTBbitl
16
OSC1
8
RB2 - PORTB bit 2
17
RAO - PORTA bit
9
RB3 - PORTB bit 3
18
RAI -PORTA bit 1
We will be using the PIC16F877 in some of the projects in this book. Figure 2.4 shows the pin
configuration of this microcontroller.
PIC16F627: This is an 18-pin microcontroller with 1024 X 14 flash program memory. The
device offers 224 bytes of RAM, 128 bytes of non-volatile EEPROM memory, 16 I/O pins, two
8-bit timers, one 16-bit timer, a watchdog, and comparator circuits. This microcontroller is simi-
lar to PIC16F84, but offers more I/O pins, more program memory, and a lot more RAM. In addi-
tion, PIC16F627 is more suited to applications which require more than one timer.
We will be using the PIC16F627 in some of the projects in this book. Figure 2.5 shows the pin
configuration of this microcontroller.
PIC16F676: This is a 14-pin microcontroller which is becoming very popular. The device offers
1024 X 14 flash program memory, 64 bytes of RAM, 12 I/O pins, 128 bytes of EEPROM, 8
The PIC microcontroller family 19
MCLR/VPP
RAO/ANO
RA1/AN1
RA2/AN2/VREF-/CVREF
RA3/AN3/VREF+
RA4/T0CKI/C1OUT
RA5/AN4/SS/C20UT
RE0/RD/AN5
RE1/WR/AN6
RE2/CS/AN7
VDD
VSS
OSC1/CLKI
OSC2/CLKO
RCO/T10SO/T1CKI
RC1/T10SI/CCP2
RC2/CCP1
RC3/SCK/SCL
RDO/PSPO
RD1/PSP1
Figure 2.4 PIC16F877 microcontroller pin configuration
RA2/AN2A/REF < ►[
RA3/AN3/CMP1 A ►[
RA4/TOCKI/CMP2 < ►[
RA5/MCLR/VPP
VSS
RBO/INT < ►[
RB1/RX/DT < ►[
RB2/TX/CK < ►[
RB3/CCP1 < ►[
► RA1/AN1
► RAO/ANO
► RA7/OSC1/CLKIN
► RA6/OSC2/CLKOUT
VDD
► RB7/T10SI/PGD
► RB6/T10SO/T1CKI/PGC
► RB5
► RB4/PGM
Figure 2.5 PIC16F627 microcontroller pin configuration
20 PIC BASIC projects
multiplexed A/D converters, each with 10-bit resolution, one 8-bit timer, one 16-bit timer, and a
watchdog. One of the advantages of this microcontroller is the built-in A/D converter.
Figure 2.6 Shows the pin configuration of this microcontroller.
VDD
RA5/T1CKI/OSC1/CLKIN <
RA4/T1G/OSC2/AN3/CLKOUT <
RA3/MCLR/VPP
RC5 <
RC4 «
RC3/AN7 <
VSS
► RA0/AN0/CIN+/ICSPDAT
► RA1/AN1/CIN-/VREF/ICSPCLK
► RA2/AN2/COUT/T0CK/INT
► RC0/AN4
► RC1/AN5
► RC2/AN6
Figure 2.6 PIC16F676 microcontroller pin configuration
PIC16F73: This is a powerful 28-pin microcontroller with 4096 X 14 flash program memory, 192
bytes of RAM, 22 I/O pins, 5 multiplexed 8-bit A/D converters, two 8-bit timers, one 16-bit timer,
watchdog, USART, and I 2 C bus compatibility. This device combines A/D converter, digital I/O,
and serial I/O capability in a 28-pin medium size package.
We will be using the PIC16F73 in some of the projects in this book. Figure 2.7 shows the pin con-
figuration of this microcontroller.
MCLR/VPP ►[
RA0/AN0 < ►[
RA1/AN1 < ►[
RA2/AN2 < ►[
RA3/AN3/VREF « ►[
RA4/TOCKI « ►[
RA5/AN4/SS < ►[
VSS ►[
OSC1/CLKIN ►[
OSC2/CLKOUT <-
-c
RC0/T1OSO/T1CKI < ►[
RC1/T10SI/CCP2 4 ►[
RC2/CCP1 < ►[
RC3/SCK/SCL < ►[
Figure 2.7 PIC16F73 microcontroller pin configuration
The PIC microcontroller family 2 1
2.3 16-bit instruction word
16-bit microcontrollers are at the high-end of the PIC microcontroller family. These microcon-
trollers cannot be used with the PicBasic compiler, but the PicBasic Pro can be used to program
them. Most of the devices in this group can operate at up to 40 MHz, have 33 I/O pins, and 3 timers.
They have 23 instructions in addition to the 35 instructions found on the 14-bit microcontrollers.
Table 2.4 lists some of the devices in this family. We will not be using any of the 16-bit micro-
controllers in the projects in this book, and I won't spend more time to describe the features of this
group. Interested readers can look at the Microchip web site at www.microchip.com.
Table 2.4 Some 16-bit microcontrollers
Microcontroller
Program
Memory
Data
RAM
Max speed
(MHz)
I/O
Ports
A/D
Converter
17C43
4096 X 16
454
33
33
-
17C752
8192 X 16
678
33
50
12
18C242
8192 X 16
512
40
23
5
18C252
16384 X 16
1536
40
23
5
18C452
16384 X 16
1536
40
34
8
All memory for the PIC microcontroller family is internal and it is usually not very easy to extend
this memory externally. No special hardware or software features are provided for extending either
the program memory or the data memory. The program memory is usually sufficient for small to
medium size projects. But the data memory is generally small and may not be enough for medium
to large projects unless a bigger and more expensive member of the family is chosen. For some
large projects even this may not be enough and the designer may have to sacrifice the I/O ports to
interface an external data memory, or to choose a microcontroller from a different manufacturer.
2.4 Inside a PIC microcontroller
Although there are many models of microcontrollers in the PIC family, they all share some com-
mon features, such as program memory, data memory, I/O ports, and timers. Some devices have
additional features such as A/D converters, USART and so on. Because of these common fea-
tures, we can look at these attributes and cover the operation of most devices in the family.
2.4. 1 Program memory (Flash)
The program memory is where your PicBasic or PicBasic Pro program resides. In early micro-
processors and microcontrollers the program memory was EPROM which meant that it had to be
erased using UV light before it could be re-programmed. Most PIC microcontrollers nowadays are
based on the flash technology where the memory chip can be erased or re-programmed using a pro-
grammer device. Most PIC microcontrollers can also be programmed without removing them from
their circuits. This process (called in-circuit serial programming, or ISP) speeds up the development
cycle and lowers the development costs. Although the program memory is mainly used to store a
program, there is no reason why it cannot be used to store constant data used in programs.
22 PIC BASIC projects
PIC microcontrollers can have program memories from 0.5 to over 16 K. A PicBasic program can
have several pages of code and still fit inside a 1 K of program memory. The width of a 14-bit pro-
gram memory is actually 14 bits wide. It is interesting to note that PICs are known as 8-bit micro-
controllers. This is actually true as far as the width of the data memory is concerned, which is
8-bits wide. Microchip calls the 14-bits a word, even though a word is actually 16-bits wide.
Although the size of the program memory can be larger than 2K, PicBasic compiler can only
work with the first 2 K which can be a limiting factor in large projects. PicBasic Pro compiler can
use all the available program memory space.
When power is applied to the microcontroller or when the MCLR input is lowered to logic 0, exe-
cution start from the Reset Vector, which is the first word of the program memory. Thus, the first
instruction executed after a reset is the one located at address of the program memory. When the
program is written in assembler language the programmer has to use special instructions (called
ORG) so that the first executable instruction is loaded into address of the program memory.
High-level languages such as PicBasic or PicBasic Pro compile your program such that the first
executable statement in your program is loaded into the first location of the program memory.
2.4.2 Data memory (RAM)
The data memory is used to store all of your program variables. This is a RAM which means that
all the data is lost when power is removed. The width of the data memory is 8-bits wide and this
is why the PIC microcontrollers are called 8-bit microcontrollers.
The data memory in a PIC microcontroller consists of banks where some models may have only
2 banks, some models 4 banks, and so on. A required bank of the data memory can be selected
under program control.
2.4.3 Register file map and special function registers
Register File Map (RFM) is a layout of all the registers available in a microcontroller and this is
extremely useful when programming the device, especially when using an assembler language.
The RFM is divided into two parts: the Special Function Registers (SFR), and the General
Purpose Registers (GPR). For example, on a PIC16F84 microcontroller there are 68 GPR regis-
ters and these are used to store temporary data. We shall see later on when programming in
PicBasic or PicBasic Pro that these registers are used to store the variables declared in a program.
SFR is a collection of registers used by the microcontroller to control the internal operations of
the device. Depending upon the complexity of the devices the number of registers in the SFR
varies. It is important that the programmer understands the functions of the SFR registers fully
since they are used both in assembly language and in high-level languages.
Depending on the model of PIC microcontroller used there could be other registers. You need not
know the operation of some of the registers since PicBasic and PicBasic Pro compiler loads these
registers automatically. For example, writing and reading from the EEPROM are controlled by
The PIC microcontroller family 23
SFR registers EEC0N1, EECON2, EEADR, and EEDATA. But fortunately, PicBasic and PicBasic
Pro compilers provide simple high-level instructions for writing to and reading from the EEPROM
and thus you do not need to know how to load these registers.
Some of the important SFR registers that you may need to configure while programming using a
high-level language are
• OPTION register
• I/O registers
• Timer registers
• INTCON register
• A/D converter registers
The functions and the bit definitions of these registers are described in detail in the following
sections.
OPTION register
This register is used to setup various internal features of the microcontroller and is named as
OPTION_REG. This is a readable and writable register which contains various control bits to
configure the on-chip timer and the watchdog timer. This register is at address 8 1 (hexadecimal)
of the microcontroller and its bit definitions are given in Figure 2.8. The OPTION REG register
is also used to control the external interrupt pin RBO. This pin can be setup to generate an inter-
rupt, for example, when it changes from logic to logic 1 . The microcontroller then suspends the
main program execution and jumps to the interrupt service routine (ISR) to service the interrupt.
Upon return from the interrupt, normal processing resumes.
For example, to configure the INT pin so that external interrupts are accepted on the rising edge
of the INT pin, the following bit pattern should be loaded into the OPTION_REG:
X1XXXXXX
Where X is a don't care bit and can be a or a 1. We shall see in the projects section on how to
configure various bits of this register.
I/O registers
These registers are used for the I/O control. Every I/O port in the PIC microcontroller has two reg-
isters: port data register and port direction control register.
Port data register has the same name as the port it controls. For example, PIC16F84 microcon-
troller has two port data registers PORTA and PORTB. A PIC16F877 microcontroller has 5 port
data registers PORTA, PORTB, PORTC, PORTD, and PORTE. An 8-bit data can be sent to any
port, or an 8-bit data can be read from the ports. It is also possible to read or write to individual
port pins. For example, any bit of a given port can be set or cleared, or data can be read from one
or more port pins at the same time.
24 PIC BASIC projects
1
6
5
4
3
2
1
RBPU
INTEDG
T0CS
T0SE
PSA
PS2
PS1
PS0
Bit 7: PORTB Pull-up Enable
1: PORTB pull-ups disabled
0: PORTB pull-ups enabled
Bit 6: INT Interrupt Edge Detect
1 : Interrupt on rising edge of INT input
0: Interrupt on falling edge of INT input
Bit 5: TMR0 Clock Source
1:T0CK1 pulse
0: Internal oscillator
Bit 4: TMRO Source Edge Select
1: Increment on HIGH to LOW of T0CK1
0: Increment on LOW to HIGH of T0CK1
Bit 3: Prescaler Assignment
1 : Prescaler assigned to Watchdog Timer
0: Prescaler assigned to TMRO
Bit 2-0: Prescaler Rate
000
1:2
001
1:4
010
1:8
on
1:16
100
1:32
101
1:64
no
1:128
in
1:256
Figure 2.8 OPTION_REG bit definitions
Ports in a PIC microcontroller are bi-directional. Thus, each pin of a port can be used as an input
or an output pin. Port direction control register configures the port pins as either inputs or outputs.
This register is called the TRIS register and every port has a TRIS register named after its port
name. For example, TRISA is the direction control register for PORTA. Similarly, TRISB is the
direction control register for PORTB and so on.
Setting a bit in the TRIS register makes the corresponding port register pin an input. Clearing a
bit in the TRIS register makes the corresponding port pin an output. For example, to make bits
The PIC microcontroller family 25
and 1 of PORTB input and the other bits output, we have to load the TRISB register with the bit
pattern.
00000011
Figure 2.9 shows the TRISB register and the direction of PORTB pins.
TRISB
1
1
PORTB
7
6
5
4 3
2
1
1 1 1 1 1 1 1 1
Figure 2.9 TRISB and PORTB direction
Port data register and port direction control registers can be accessed directly using the PicBasic
Pro compiler. For example, as we shall see in a later chapter, TRISB register can be set to 3 and
data can be read from PORTB into a variable named CNT by the PicBasic Pro instructions.
TRISB = 3
CNT = PORTB
The PicBasic compiler has no direct register control instructions and as we shall see in a later
chapter, we have to use the PEEK and POKE instructions. PEEK is used to read data from a regis-
ter and POKE is used to send data to a register.
When we use the PEEK and POKE instructions we have to specify the register address of the regis-
ter we wish to access. The register addresses of port registers are (the "$" character specifies that
the number is in hexadecimal format)
Ports
Address (Hexadecimal)
PORTA
$05
PORTB
$06
PORTC
$07
PORTD
$08
PORTE
$09
TRISA
$85
TRISB
$86
TRISC
$87
TRISD
$88
TRISE
$89
26 PIC BASIC projects
Thus, for the above example, the required PicBasic instructions will be
POKE $86, 3
PEEK $06, CNT
We shall see in the next chapter how to use symbols in PicBasic language to make our programs
clearer and easier to maintain.
Timer registers
Depending on the model used, some PIC microcontrollers have only one timer, and some may
have up to 3 timers. In this section we shall look at the PIC16F84 microcontroller which has only
one timer. The extension to several timers is similar and we shall see in the projects section how
to use more than one timer.
The timer in the PIC16F84 microcontroller is an 8-bit register (called TMRO) which can be used
as a timer or a counter. When used as a counter, the register increments each time a clock pulse is
applied to pin T0CK1 of the microcontroller. When used as a timer, the register increments at a
rate determined by the system clock frequency and a prescaler selected by register OPTION_REG.
Prescaler rates vary from 1:2 to 1:256. For example, when using a 4 MHz clock, the basic instruc-
tion cycle is 1 (jls (the clock is internally divided by four). If we select a prescaler rate of 1 : 16, the
counter will be incremented at every 16 (jls.
The TMRO register has address 01 in the RAM which can be loaded using the POKE instruction
in PicBasic, or by accessing the TMRO register directly in PicBasic Pro.
A timer interrupt is generated when the timer overflows from 255 to 0. This interrupt can be enabled
or disabled by our program. Thus, for example, if we require to generate interrupts at 200 (xs intervals
using a 4 MHz clock, we can select a prescaler value of 1:4 and enable timer interrupts. The timer
clock rate is then 4 |xs. For a time-out of 200 (jls, we have to send 50 clocks to the timer. Thus, the
TMRO register should be loaded with 256 — 50 = 206, i.e. a count of 50 before an overflow occurs.
The watchdog timer's oscillator is independent from the CPU clock and the time-out is 18 ms. To
prevent a time-out condition the watchdog must be reset periodically via software. If the watchdog
timer is not reset before it times out, the microprocessor will be forced to jump to the reset address.
The prescaler can be used to extend the time-out period and valid rates are 1, 2, 4, 8, 16, 32, 64, and
128. For example, when set to 128, the time out period is about 2 s (18 X 128 = 2304 ms). The
watchdog timer can be disabled during programming of the device if it is not used.
Since the timer is very important part of the PIC microcontrollers more detailed information is
given on its operation below.
TMRO and watchdog
TMRO and a watchdog are found nearly in all PIC microcontrollers. Figure 2.10 shows the func-
tional diagram of TMRO and the watchdog circuit. The operation of the watchdog circuit is as
described earlier and only the TMRO circuit is described in this section.
The PIC microcontroller family 27
The source of input for TMRO is selected by bit TOCS of OPTION_REG and it can be either
from the microcontroller oscillator / osc divided by 4, or it can be an external clock applied to the
RA4/T0CK1 input. Here, we will only look at using the internal oscillator. If a 4 MHz crystal is used
the internal oscillator frequency is/ osc /4 = 1 MHz which corresponds to a period of T = II f = 10 -6 ,
or 1 (jls. TMRO is then selected as the source for the prescaler by clearing PSA bit of OPTION_REG.
The required prescaler value is selected by bits PSO to PS2 as shown in Figure 2.8. Bit PSA should
then be cleared to to select the prescaler for the timer. All the bits are configured now and TMRO
register increments each time a pulse is applied by the internal oscillator. TMRO register is 8-bits
wide and it counts up to 255, then creates an overflow condition, and continues counting from 0.
When TMRO changes from 255 to it generates a timer interrupt if timer interrupts and global inter-
rupts are enabled (see INTCON register. Interrupt will be generated if GIE and TMRO bits of INT-
CON are both set to 1). See the Section 2.4.6 on Interrupts for more information.
f /4
'ncr' ■
'OSC
RA4/
T0CK1
TOSE
TOCS
Watchdog
Timer
Prescaler
PSA
PSA
PS2:PS0
TMRO
Overflow
WDT
Timeout
PSA
Figure 2.10 TMRO and watchdog circuit
By loading a value into the TMRO register we can control the count until an overflow occurs. The
formula given below can be used to calculate the time it will take for the timer to overflow (or to
generate an interrupt) given the oscillator period, value loaded into the timer and the prescaler value.
where
Overflow time
T
± OSC
Prescaler
TMRO
Overflow time = 4 X T osc X Prescaler X (256 - TMRO)
is in (jls,
is the oscillator period in (xs,
is the prescaler value chosen using OPTION_REG
is the value loaded into TMRO register.
(2.1)
For example, assume that we are using a 4 MHz crystal, and the prescaler chosen as 1 :8 by setting
bits PS2:PS0 to "010". Also assume that the value loaded into the timer register TMRO is decimal
100. The overflow time is then given by
4 MHz clock has a period, T= \lf= 0.25 |jls
28 PIC BASIC projects
Using the above formula,
Overflow time = 4 X 0.25 X 8 X (256 - 100) = 1248 |uls.
Thus, the timer will overflow after 1 .248 ms and a timer interrupt will be generated if the timer
interrupt and global interrupts are enabled.
What we normally need is to know what value to load into the TMRO register for a required
Overflow time. This can be calculated by modifying Eq. (2.1) as
TMRO = 256 - (Overflow time)/(4 X T osc X Prescaler)
(2.2)
For example, suppose that we want an interrupt to be generated after 500 (jls and the clock and the
prescaler values are as before. The value to be loaded into the TMRO register can be calculated
using Eq. (2.2) as
TMRO = 256 - 500/(4 X 0.25 X 8) = 193.5
The nearest number we can load into TMRO register is 193.
Table 2.5 gives the values that should be loaded into TMRO register for different Overflow times.
In this table a 4 MHz crystal is assumed and the table gives as the prescaler value is changed from
2 to 256.
Table 2.5 Required TMRO values for different overflow times
Time to
overflow (jjls)
Prescaler
2
4
8
16
32
64
128
256
100
206
231
243
250
253
254
-
-
200
156
206
231
243
250
253
254
-
300
106
181
218
237
246
251
253
255
400
56
156
206
231
243
250
253
254
500
6
131
193
224
240
248
252
254
600
-
106
181
218
237
16
251
253
700
-
81
168
212
234
245
250
253
800
-
56
156
206
231
243
250
253
1,000
-
6
131
193
225
240
248
252
5,000
-
-
-
-
100
178
77
236
10,000
-
-
-
-
-
100
178
217
20,000
-
-
-
-
-
-
100
178
30,000
-
-
-
-
-
-
-
139
40,000
-
-
-
-
-
-
-
100
50,000
-
-
-
-
-
-
-
60
60,000
-
-
-
-
-
-
-
21
The PIC microcontroller family 29
TMR1
Although TMRO is the basic timer found nearly in all PIC microcontrollers, some devices have
several timers, e.g. TMRO, TMR1, and TMR2. Additional timers give added functionality to a
microcontroller. In this section the operation of TMR1 will be described in detail.
TMR1 is a 16-bit timer, consisting of two 8-bit registers TMR1H and TMR1L. As shown in Figure
2.1 1, a prescaler is used with TMR1 and the available prescaler values are only 1, 2, 4, and 8.
o
TIOSO
f /4
'osc' ^
i
-
Prescaler
-►
Synchronise
4
i
L
T1
&
TMR1H
Overflow
►
TMR1L
TMR10N
T1CKPS0
T1CKPS1
TMR1CS
Figure 2.11 TMR1 structure
Register T ICON controls the operation of TMR1. The bit definition of this register is shown in Figure
2.12. TMR1 can operate either as a timer or as a counter, selected by bit TMR1CS of T ICON. When
operated in timer mode, TMR1 increments every oscillator frequency / osc /4. TMR1 can be enabled or
disabled by setting or clearing control bit TMRION. TMR1 can count from to 65,535 and it gener-
ates an overflow when changing from 65,535 to 0. A timer interrupt is generated if the TMR1 inter-
rupt enable bit TMR1IE is enabled and also the global interrupts are enabled by register INTCON.
When TMR1 is operated in counter mode, it increments on every rising edge (from logic to
logic 1 ) of the clock input.
TMR2
TMR2 is an 8-bit timer with a prescaler and a postscaler and it has an 8-bit period register PR2.
This timer is controlled by register T2CON whose bit definitions are given in Figure 2.13. The
prescaler options are 1, 4, and 16 only and are selected by T2CKPS1 and T2CKPS0 bits of
T2CON. TMR2 increments from 0, until it matches PR2, and then resets to on the next cycle.
Then the cycle is repeated. TMR2 can be shut off by clearing TMR20N of T2CON register to
minimise power consumption.
INTCON register
This is the interrupt control register. This register is at address and 8B (hexadecimal) of the
microcontroller RAM and the bit definitions are given in Figure 2.14. For example, to enable
30 PIC BASIC projects
1
6
5
4
3
2
1
—
—
TICKPS1
TICKPSO
TIOSCEN
TISYNC
TMR1CS
TMR10N
Bit 7: Unused
Bit 6: Unused
Bit 5-4: Timerl Input Clock Prescale Select Bits
11 1:8 prescale value
10 1 :4 prescale value
01 1:2 prescale value
00 1:1 prescale value
Bit 3: Timerl Oscillator Enable Bit
1 : Oscillator is enabled
0: Oscillator is disabled
Bit 2: Timerl External Clock Input Synchronisation Select Bit
WhenTMRlCS = 1:
1 : Do not synchronise external clock input
0: Synchronise external clock input
WhenTMRlCS = 0:
This bit is ignored. Timerl uses internal clock
Bit 1: Timerl Clock Source Select Bit
1: External clock from pin TIOSO (on rising edge)
0: Internal clock (/osc/4)
Bit 0: Timerl On Bit
1: Enable Timerl
0: Stops Timerl
Figure 2.12 T1CON bit definitions
interrupts so that external interrupts from pin INT (RB0) can be accepted on a PIC16F84, the fol-
lowing bit pattern should be loaded into register INTCON:
1XX1XXXX
Similarly, to enable timer interrupts, bit 5 of INTCON must be set to 1.
A/D converter registers
The A/D converter is used to interface analogue signals to the microcontroller. The A/D converts
analogue signals (e.g. voltage) into digital form so that they can be connected to a computer. A/D
converter registers are used to control the A/D converter ports. On most PIC microcontrollers
equipped with A/D, PORTA pins are used for analogue input and these port pins are shared
between digital and analogue functions.
The PIC microcontroller family 3 1
7
6
5
4
3
2
1
—
T0UTPS3
T0UTPS2
T0UTPS1
TOUTPSO
TMR20N
T2CKPS1
T2CKPS0
Bit 7: Unused
Bit 6-3: Timer2 Output Postscale Select Bits
0000 1:1 Postscale
0001 1:2 Postscale
0010 1:3 Postscale
1111 1:16 Postscale
Bit 2: Timer2 On Bit
1 : Timer2 is On
0: Timer2 is Off
Bit 1-0: Timer2 Clock Prescale Select Bits
00
Prescaler is 1
01
Prescaler is 4
10
Prescaler is 16
11
Prescaler is 16
Figure 2.13 T2CON bit definitions
PIC16F876 includes 5 A/D converters. Similarly, PIC16F877 includes 8 A/D converters. There is
actually only one A/D converter as shown in Figure 2.15 and the inputs are multiplexed and they
share the same converter. The width of the A/D converter can be 8-bits or 10-bits. Both
PIC16F876 and PIC16F877 have 10-bit converters. PIC16F73 has 8-bit converters. An A/D con-
verter requires a reference voltage to operate. This reference voltage is chosen by programming
the A/D converter registers and is typically +5 V Thus, if we are using a 10-bit converter (1024
quantisation levels) the resolution of our converter will be 5/1024 = 0.00488 V, or 4.88 mV, i.e.
we can measure analogue voltages with a resolution of 4.88 mV For example, if the measured
analogue input voltage is 4.88 mV we get the 10-bit digital number "0000000001", if the ana-
logue input voltage is 2 X 4.88 = 9.76 mV, the 10-bit converted number will be "0000000010",
if the analogue input voltage is 3 X 4.88 = 14.64 mV, the converted number will be
"0000000011", and so on.
In a similar way, if the reference voltage is +5 V and we are using an 8-bit converter (256 quant-
isation levels), the resolution of the converter will be 5/256 = 19.53 mV For example, if the
measured input voltage is 19.53 mV we get the 8-bit number "00000001", if the analogue input
voltage is 2 X 19.53 = 39.06 mV we get the 8-bit number "00000010", and so on.
The A/D converter is controlled by registers ADCON0 and ADCON1. The bit pattern of ADCON0
is shown in Figure 2.16. ADCON0 is split into four parts, the first part consists of the highest two
32 PIC BASIC projects
7
6
5
4
3
2
1
GIE
EEIE
TOIE
INTE
RBIE
TOIF
INTF
RBIF
Bit 7: Global Interrupt Enable
1 : Enable all un-masked interrupts
0: Disable all interrupts
Bit 6: EE Write Complete Interrupt
1 : Enable EE write complete interrupt
0: Disable EE write complete interrupt
Bit 5: TMRO Overflow Interrupt
1: Enable TMRO interrupt
0: Disable TMRO interrupt
Bit 4: INT External Interrupt
1 : Enable INT External Interrupt
0: Disable INT External Interrupt
Bit 3: RB Port Change Interrupt
1 : Enable RB port change interrupt
0: Disable RB port change interrupt
Bit 2: TMRO Overflow Interrupt Flag
1 : TMRO has overflowed
0: TMRO did not overflow
Bit 1: INT Interrupt Flag
1 : INT interrupt occurred
0: INT interrupt did not occur
Bit 0: RB Port Change Interrupt Flag
1: One or more of RB4-RB7 pins changed state
0: None of RB4-RB7 changed state
Figure 2.14 INTCON register bit definitions
bits ADCS 1 and ADCS0 and they are used to select the conversion clock. The internal RC oscilla-
tor or the external clock can be selected as the conversion clock as in the following table:
00
01
10
11
External clock/2
External clock/8
External clock/32
Internal RC clock
The PIC microcontroller family 33
Channel
Channel 1
Channel 2
Channel 3
Channel 4
Channel 5
Channel 6
Channel 7
\
Multiplexer
Figure 2.15 Multiplexed A/D structure
A/D
Converter
Converted
Digital
Signal
7
6
5
4
3
2
1
ADCS1
ADCSO
CHS2
CHS1
CHSO
GO/DONE
—
ADON
Bit 7-6: A/D Converter Clock Select
00 /osc/2
01 /asc/8
10 /oac/32
1 1 Internal RC oscillator
Bit 5-3: A/D Channel Select
000
Channel
001
Channel 1
010
Channel 2
011
Channel 3
100
Channel 4
101
Channel 5
110
Channel 6
111
Channel 7
Bit 2: GO/DONE Bit
1 : Start conversion
0: A/D conversion is complete
Bit 1: Not used
Bit 0: ADON Bit
1: Turn ON A/D circuit
0: Turn OFF A/D circuit
Figure 2.16 ADCON0 bit definitions
34 PIC BASIC projects
The second part of ADCONO consists of the three bits CHS2, CHS1, and CHSO. These are the
channel select bits, and they select which input pin is routed to the A/D converter. The selection
is as follows:
CHS2:CHS1:CHS0
000 Channel
001 Channel 1
010 Channel 2
011 Channel 3
100 Channel 4
101 Channel 5
110 Channel 6
111 Channel 7
The third part of ADCONO is the single GO/DONE bit. This bit has two functions: first, by set-
ting the bit it starts the A/D conversion. Second, the bit is cleared when the conversion is complete
and this bit can be checked to see whether or not the conversion is complete.
The fourth part of ADCONO is also a single bit ADON which is set to turn on the A/D converter
circuitry.
ADRESH and ADRESL are the A/D converter result registers. ADRESL is the low byte and
ADRESH is the upper 2 bits (if a 10-bit converter is used). We shall see how to configure the
result of the conversion later.
ADCON1 is the second A/D control register. This register controls the format of converted data and
mode of the PORTA inputs. The bit format of this register is shown in Figure 2.17. Bit 7 is called
ADFM and when this bit is the result of the A/D conversion is left justified, when it is 1, the result
of the A/D conversion is right justified. If we have an 8-bit converter we can clear ADFM and just
read ADRESH to get the 8-bit converted data. If we have a 10-bit converter we can set ADFM to 1
and the 8 bits of the result will be in ADRESL, 2 bits of the result will be in the lower bit positions
of ADRESH. The remaining 6 positions of ADRESH (bit 2 to bit 7) will be cleared to zero.
Bits PCFG0-3 control the mode of PORTA pins. As seen in Figure 2. 17, a PORTA pin can be pro-
grammed to be a digital pin or an analogue pin. For example, if we set PCFG0-3 to "01 10" then
all PORTA pins will be digital I/O pins. PCFG0-3 bits can also be used to define the reference
voltage for the A/D converter. As we shall see in the projects section of the book, the reference
voltage Vref + is usually set to be equal to the supply voltage (Vdd), and Vref — is set to be equal
to Vss. This makes the A/D reference voltage to be +5 V.
2.4.4 Oscilla tor circuits
An Oscillator circuit is used to provide a microcontroller with a clock. A clock is needed so that
the microcontroller can execute a program.
The PIC microcontroller family 35
7
6
5
4
3
2
1
ADFM
—
—
—
PCFG3
PCFG2
PCFG1
PCFGO
Bit 7: A/D Converter Result Format Select
1: A/D converter output is right justified
0: A/D converter output is left justified
Bit 6: Not used
Bit 5: Not used
Bit 4: Not used
Bit 3-0: Port Assignment and Reference Voltage Selection
(see Table below)
PCFG3-
PCFGO
AN7
AN6
AN5
AN4
AN3
AN2
AN1
AN0
Vref+
Vref-
0000
A
A
A
A
A
A
A
A
Vdd
Vss
0001
A
A
A
A
Vref+
A
A
A
RA3
Vss
0010
D
D
D
A
A
A
A
A
Vdd
Vss
0011
D
D
D
A
Vref+
A
A
A
RA3
Vss
0100
D
D
D
D
A
D
A
A
Vdd
Vss
0101
D
D
D
D
Vref+
D
A
A
RA3
Vss
0110
D
D
D
D
D
D
D
D
Vdd
Vss
0111
D
D
D
D
D
D
D
D
Vdd
Vss
1000
A
A
A
A
Vref+
Vref-
A
A
RA3
RA2
1001
D
D
A
A
A
A
A
A
Vdd
Vss
1010
D
D
A
A
Vref+
A
A
A
RA3
Vss
1011
D
D
A
A
Vref+
Vref-
A
A
RA3
RA2
1100
D
D
D
A
Vref+
Vref-
A
A
RA3
RA2
1101
D
D
D
D
Vref+
Vref-
A
A
RA3
RA2
1110
D
D
D
D
D
D
D
A
Vdd
Vss
mi
D
D
D
D
Vref+
Vref-
D
A
RA3
RA2
Figure 2.17 ADCON1 bit definitions
36 PIC BASIC projects
PIC microcontrollers have built-in oscillator circuits and this oscillator can be operated in one of
five modes.
• LP - Low-power crystal
• XT - Crystal/resonator
• HS - High-speed crystal/resonator
• RC resistor - capacitor
• No external components (only on some PIC microcontrollers).
In LP, XT, or HS modes, an external oscillator can be connected to the OSC1 input as shown in
Figure 2.18. This can be a crystal-based oscillator, or simple logic gates can be used to design an
oscillator circuit.
External
Clock
Figure 2.18 Using an external oscillator
Crystal operation
As shown in Figure 2. 19, in this mode of operation an external crystal and two capacitors are con-
nected to the OSC1 and OSC2 inputs of the microcontroller. The capacitors should be chosen as
in Table 2.6. For example, with a crystal frequency of 4 MHz, two 22 pF capacitors can be used.
16 I ■ 15
C1 = =~l I = z C2
22p?T 4 MHz ~T~22pF
Figure 2.19 Crystal oscillator circuit
The PIC microcontroller family 37
Table 2.6 Capacitor selection for crystal
operation
Mode
Frequency
C1,C2
LP
32 kHz
68-100 pF
LP
200 kHz
15-33 pF
XT
100 kHz
100-150 pF
XT
2 MHz
15-33 pF
XT
4 MHz
15-33 pF
HS
4 MHz
15-33 pF
HS
10 MHz
15-33 pF
Resonator operation
Resonators are available from 4 to about 8 MHz. They are not as accurate as crystal-based oscil-
lators. Resonators are usually 3-pin devices and the two pins at either sides are connected to
OSC1 and OSC2 inputs of the microcontroller. The middle pin is connected to the ground. Figure
2.20 shows how a resonator can be used in a PIC microcontroller circuit.
Figure 2.20 Resonator oscillator circuit
RC oscillator
For applications where the timing accuracy is not important we can connect an external resistor
and a capacitor to the OSC1 input of the microcontroller as in Figure 2.21. The oscillator fre-
quency depends upon the values of the resistor and capacitor (see Table 2.7), the supply voltage,
and to the temperature. For most applications, using a 5K resistor with a 20 pF capacitor gives
about 4 MHz and this may be acceptable in non-time critical applications.
38 PIC BASIC projects
Vdd
i
R
Cd=
PIC
Microcontroller
0SC1
Figure 2.21 RC oscillator circuit
Table 2.7 RC oscillator component selection
c
R
Frequency
20 pF
5K
4.61MHz
10K
2.66 MHz
100 K
311kHz
lOOpF
5K
1.34 MHz
10K
756 kHz
100 K
82.8 kHz
300 pF
5K
428 kHz
10K
243 kHz
100 K
26.2 kHz
Internal oscillator
Some PIC microcontrollers (e.g. PIC12C672 and PIC16F628) have built-in oscillator circuits and
they do not require any external timing components. The built-in oscillator is usually set to oper-
ate at 4 MHz and is selected during the programming of the device. For example, the PIC16F62X
series of PIC microcontrollers can be operated with an internal resistor- capacitor-based 4 MHz
oscillator (called mode INTRC). Additionally, a single resistor can be connected to pin RA7 of the
microcontroller to create a variable oscillator frequency (called ER mode). For example, in the
PIC16F62X microcontroller OSC1 and OSC2 pins are shared with the RA7 and RA6 pins respec-
tively. The internal oscillator frequency can be set by connecting a resistor to pin RA7 as shown
in Figure 2.22. Depending on the value of this resistance the oscillator frequency can be selected
from 200 kHz to 10.4 MHz (see Table 2.8). When used in this mode, pin RA7 is not available as a
digital I/O pin.
The internal oscillator frequency of some microcontrollers (e.g. PIC16F630) can be calibrated
so that more accurate timing pulses can be generated in time critical applications (e.g. in serial
communications). In these microcontrollers an oscillator register called OSCCAL is used for the
The PIC microcontroller family 39
R
PIC
16F628
0SC1
(RA7)
Figure 2.22 Changing the internal oscillator frequency
Table 2.8 Resistor value for the internal oscillator
Resistance
Frequency
10.4 MHz
IK
10.0 MHz
10K
7.4 MHz
20 K
5.3 MHz
47 K
3 MHz
100 K
1.6 MHz
220 K
800 kHz
470 K
300 kHz
1M
200 kHz
calibration of the oscillator frequency. A factory-calibrated oscillator constant is loaded into the
last location of the memory. By copying this constant value into the oscillator register we can have
a more accurate 4 MHz clock frequency for our microcontroller. It is also possible to modify the
OSCCAL register values in order to fine-tune the oscillator frequency.
The following PicBasic and PicBasic Pro statements can be used to copy the oscillator calibration
constant from the last memory location into the OSCCAL register. These commands must be
declared at the beginning of our programs.
DEFINE OSCCAL_l K 1
DEFINE OSCCAL 2 K 1
For 1 K core-size microcontrollers
For 2 K core-size microcontrollers
Note that the oscillator constant can be erased during the erasing of the program memory. You
should make a note of the value at the last location of the program memory before erasing the
memory. If this value is known it can be loaded directly into the OSCCAL register at the begin-
ning of our programs as shown below (here it is assumed that the constant is $24).
OSCCAL = $24
40 PIC BASIC projects
2.4.5 Reset circuit
Reset is used to put the microcontroller into a known state. Normally when a PIC microcontroller is
reset execution starts from address of the program memory. This is where the first executable user
program resides. The reset action also initialises various SFR registers inside the microcontroller.
PIC microcontrollers can be reset when one of the following conditions occur:
• Reset during power on (POR - Power On Reset)
• Reset by lowering MCLR input to logic
• Reset when the watchdog overflows.
As shown in Figure 2.23, a PIC microcontroller is normally reset when power is applied to the
chip and when the MCLR input is tied to the supply voltage through a 4.7 K resistor.
+Vdd
4.7K
MCLR
PIC
Microcontroller
Figure 2.23 Using the power on reset
There are many applications where we want to reset the microcontroller, e.g. by pressing an exter-
nal button. The simplest circuit to achieve an external reset is shown in Figure 2.24. In this circuit,
the MCLR input is normally at logic 1 and the microcontroller is operating normally. When the
reset button is pressed this pin goes to logic and the microcontroller is reset. When the reset but-
ton is released the microcontroller starts executing from address of the program memory.
4.7K
Button
Figure 2.24 Using an external reset button
The PIC microcontroller family 4 1
2.4.6 Interrupts
Interrupts are an important feature of all microcontrollers. An interrupt can either occur asyn-
chronously or synchronously. Asynchronous interrupts are usually external events which inter-
rupt the microcontroller and request service. For example, pin INT (RBO) of a PIC16F84
microcontroller is the external interrupt pin and this pin can be used to interrupt the microcon-
troller asynchronously, i.e. the interrupt can occur at any time independent of the program being
executed inside the microcontroller. Synchronous interrupts are usually timer interrupts, such as
the timer overflow generating an interrupt.
Depending on the model used, different PIC microcontrollers may have different number of inter-
rupt sources. For example, PIC16F84 microcontroller has the following four sources of interrupts:
• External interrupt from INT (RBO) pin
• TMRO interrupt caused by timer overflow
• External interrupt when the state of RB4, RB5, RB6, or RB7 pins change
• Termination of writing data to the EEPROM.
Interrupts are enabled and disabled by the INTCON register. Each interrupt source has two bits to
control it. One enables interrupts, the other one detects when an interrupt occurs. There is a com-
mon bit called GIE (see INTCON register bit definitions) which can be used to disable all sources
of interrupts.
The INTCON control bits of various interrupt sources are
Interrupt Source Enabled by Completion Status
External interrupt from INT INTE = 1 INTF = 1
TMRO interrupt TOIE = 1 TOIF = 1
RB4-RB7 state change RBIE = 1 RBIF = 1
EEPROM write complete EEIE = 1
Whenever an interrupt occurs the microcontroller jumps to the ISR. On low-end microcontrollers
(e.g. PIC16F84 or PIC16F628) all interrupt sources use address 4 in program memory as the start
of the ISR. Because all interrupts use the same ISR address we have to check the interrupt com-
pletion status to detect which interrupt has occurred when multiple interrupts are enabled.
The completion status has to be cleared to zero if we want the same interrupt source to be able to
interrupt again.
Assuming that we wish to use the external interrupt (INT) input, and interrupts should be
accepted on the low to high transition of the INT pin, the steps before and after an interrupt are
summarised below.
• Set the direction of the external interrupt to be on rising edge by setting INTEDG = 1 in regis-
ter OPTION REG.
42 PIC BASIC projects
• Enable INT interrupts by setting INTE = 1 in register INTCON.
• Enable global interrupts by setting GIE = 1 in register INTCON.
• Carry out normal processing. When interrupt occurs program will jump to the ISR.
• Carry out the required tasks in the ISR routine.
• At the end of the ISR, re-enable the INT interrupts by clearing INTF = 0.
As we shall see in the projects section of the book, PicBasic Pro language has special instructions
for handling interrupts.
2.4.7 The configuration word
PIC microcontrollers have a special register called the Configuration Word. This is a 14- bit register
and is mapped in program memory 2007 (hexadecimal). This address is beyond the user program-
memory space and cannot be directly accessed in a program. This register can be accessed during
the programming of the microcontroller.
The configuration word stores the following information about a PIC microcontroller:
• Code protection bits: These bits are used to protect blocks of memory so that they cannot
be read.
• Power-on timer enable bit.
• Watchdog (WDT) timer enable bit.
• Oscillator selection bits: The oscillator can be selected as XT, HS, LP, RC, or internal (if supported
by the microcontroller).
For example, in a typical application we can have the following configuration word selection during
the programming of the microcontroller:
• Code protection OFF
• XT oscillator selection
• WDT disabled
• Power-up timer enables.
2.4.8 I/O interface
A PIC microcontroller port can source and sink 25 mA of current. When sourcing current, the
current is flowing out of the port pin, and when sinking current, the current is flowing into the pin.
When the pin is sourcing current, one pin of the load is connected to the microcontroller port and
the other pin to the ground (see Figure 2.25a). The load is then energised when the port output is
at logic 1 . When the pin is sinking current, one pin of the load is connected to the supply voltage
and the other pin to the output of the port (see Figure 2.25b). The load is then energised when the
port output is at logic 0.
The PIC microcontroller family 43
Output
Port
PIC
Microcontroller
Load
Figure 2.25a Current sourcing
A+Vdd
Load
Figure 2.25b Current sinking
Some useful interface circuits are given in this section.
LED interface
LEDs come in many different sizes, shapes, and colours. The brightness of an LED depends on
the current through the device. Some small LEDs operate with only a few milliamperes of cur-
rent, while standard size LEDs consume about 10 mA of current for normal brightness. Some
very bright LEDs consume 15-20mA of current. The voltage drop across an LED is about 2 V,
but the voltage at the output of a microcontroller port is about 5 V when the port is at logic 1 level.
As a result of this it is not possible to connect an LED directly to a microcontroller output port.
What is required is a resistor to limit the current in the circuit.
If the output voltage of the port is 5 V and the voltage drop across the LED is 2 V, we need to drop
3 V across the resistor. If we assume that the current through the LED is 10 mA, we can calculate
the value of the required resistor as
R =
5 - 2V
10m A
3V
10 mA
= 0.3K
The nearest physical resistor we can use is 330 fl. Figure 2.26 shows how an LED can be connected
to an output port pin in current source mode. In this circuit the LED will be ON when the port out-
put is set to logic 1. Similarly, Figure 2.27 shows how an LED can be connected to an output port
pin in current sink mode. In this circuit the LED will be ON when the port output is at logic 0.
44 PIC BASIC projects
Higher current load interface
The circuits given in Figures 2.26 and 2.27 work fine for an LED, or for any other device whose
current requirement is less than 25 mA. What do we do if we wish to operate a load with a higher
current rating? e.g. a 12 V filament lamp. The answer is that we have to use a switching device,
e.g. a transistor or a relay.
Output
Port
PIC
Microcontroller
R
-^
LED
Figure 2.26 Connecting an LED in current source mode
a +Vdd
-^.LED
Figure 2.27 Connecting an LED in current sink mode
Figure 2.28 shows how we can drive a small lamp from our port pin using a bipolar transistor. In this
circuit, when the port output pin is at logic 1 , current flows through the resistor and turns the transis-
tor ON, effectively connecting the bottom end of the lamp to ground. It is important to realise that the
positive supply to the lamp is not related to the PIC supply voltage and while the PIC is operating
from +5 V, the lamp can be operated from a 12 V supply. The current capability depends upon the type
of transistor used and several hundred milliamperes can be achieved with any type of small npn tran-
sistors. For higher currents, bipolar power transistors, or preferably MOSFET transistors can be used.
Relay interface
When we want to switch inductive loads such as relays we have to use a diode in the circuit to pre-
vent the transistor from being damaged (see Figure 2.29). An inductive load can generate a back
EMF which could easily damage a transistor. By connecting a diode in reverse bias mode this
back EMF is dissipated without damaging the transistor.
The PIC microcontroller family 45
Lamp
Figure 2.28 Driving a lamp using a transistor
+V
ear.
Output
Port
PIC
Microcontroller
1K
- t h
L
Relay contacts
1/
■^
npn
Figure 2.29 Driving an inductive load (e.g. a relay)
Since we can drive a relay, we can connect any load to the relay outputs as long as we do not
exceed the contact ratings of the relay. Figure 2.30 shows how a mains lamp can be operated from
the microcontroller output port using a relay. The relay could also be operated using a MOSFET
power transistor. In this circuit the mains lamp will turn ON when the output port of the micro-
controller is a logic 1 .
Output
Port
PIC
Microcontroller
1K
+V
C3^
IK
npn
Mains Lamp
^ o
220 V
-O
Figure 2.30 Driving a mains bulb using a relay
46 PIC BASIC projects
Button input
One of the most common type of input is a button (a push-button switch) input where the user can
change the state of an input pin by pressing a button. Basically, button input can be in two different
ways: active low and active high. As shown in Figure 2.31 in active low implementation, the micro-
controller input pin is connected to the supply voltage using a resistor (this is also called a pull-up
resistor) and the button is connected between the port pin and ground. Normally the microcontroller
input is pulled to logic 1 by the resistor. When the button is pressed the input is forced to ground
potential which is logic 0. The change of state in the input pin can be determined by a program.
l\
Input
Port
PIC
o
Microcontroller
~
10K
\
Figure 2.31 Active low-button input
Some ports in PIC microcontrollers have internal pull-up resistors (e.g. PORTB) and these resis-
tors can be enabled by clearing bit 7 (RBPU) of register INTCON to zero. When one of this port
pins is used for button input there is no need to use an external pull-up resistor and the button can
simply be connected between the port pin and ground.
A button can also be connected in active high mode as shown in Figure 2.32. In this configuration
the button is connected between the supply voltage and the port pin. A resistor (this is also called
a pull-down resistor) is connected between the port pin and ground. Normally, the port pin is at
logic 0. When the button is pressed the port pin goes to the supply voltage which is logic 1 .
Input
Port
o
PIC
Microcontroller
.
10K
Figure 2.32 Active high-button input
One of the problems with mechanical switches is that when a switch closes its metal parts com-
press and relax and this causes the switch to open and close several times quickly. The problem
is that the microcontroller can read the switch so fast that it can see the switch open and close
The PIC microcontroller family 47
during the bouncing of the metal parts and this may cause wrong switch state to be read by the
microcontroller. One way to eliminate this switch-bouncing problem is to delay reading the input
after the switch state changes. For example, when we detect the switch is pressed, we may wait
about 10 ms before we read the state of the switch.
In Figures 2.31 and 2.32, we have seen how simple buttons can be connected to a microcontroller
port. It is also possible to connect to an input pin a switching transistor, the output of another IC,
or simply the output of another PIC port pin. Figure 2.33 shows how a switching transistor can be
connected as an input. In this circuit the transistor acts like an inverting switch. When the transis-
tor input voltage is V, the transistor is in OFF state and the port pin is at logic 1 level. When the
transistor input voltage is +5 V the transistor turns ON and its collector-emitter voltage drops to
V, making the port pin logic 0. One thing nice about this circuit is that the transistor input volt-
age does not need to be +5 V to turn the transistor ON, it could easily be 9 or 12 V.
A+V
Input
Figure 2.33 Transistor input
The input ports of PIC microcontrollers are protected by internal diodes for over- voltage and
under- voltage. Thus, the voltage on a pin can exceed the supply voltage, or it can go below the
ground voltage without causing any harm to the microcontroller. The RS232 serial communica-
tion lines operate with ± 12 V and we can usually connect these lines directly to the input ports
using resistors without damaging the microcontroller.
2.5 Exercises
1. What is a flash memory? Explain the differences between a flash program memory and an
EPROM program memory. Which one would you use in program development?
2. What is an EEPROM memory? Explain where you might use it. Give an example PIC micro-
controller which has EEPROM memory.
3. Explain briefly the bit definitions of the INTCON register. Where would you use bit 6 of this
register?
4. Explain how an I/O port direction is controlled in a PIC microcontroller. In an application it
is required to make bits 0, 2, 4, and 6 of PORTB as input ports. What value would you have
to load into the TRIS register?
48 PIC BASIC projects
5. In an application it is required to make all PORTB pins as inputs and all PORT C pins as out-
puts. What value would you load into the TRIS registers?
6. Explain what registers are used to control the A/D on a PIC microcontroller. What are the
ADRESH and ADRESL registers?
7. In an application it is required to have 3 digital ports and 5 analogue ports. What value would
you have to load into register AD CON 1?
8. Explain how you can connect an external crystal to a PIC microcontroller. What capacitor
values would you choose for a 10 MHz crystal?
9. What are the advantages of using a resonator instead of a crystal?
10. In a simple application where the timing accuracy is not important it is required to operate a
PIC microcontroller with a clock frequency of around 2 MHz. What value of resistor and
capacitor would you use in the timing circuit?
11. Explain how the internal oscillator can be used on a PIC16F628 microcontroller. It is
required to use an internal clock frequency of around 3 MHz. What value of resistor would
you use and where would you connect this resistor?
12. Explain what happens when a PIC microcontroller is reset. How can you achieve the reset
action by using external components?
13. Explain the differences between TMRO and TMR1 of a PIC microcontroller.
14. It is required to load the TMRO register to generate an overflow in 250 ms. Assuming the
clock frequency is 4 MHz, choose suitable values for the prescaler and TMRO.
15. In an application it is required to connect 8 small LEDs to PORTB pins of a PIC 16F84 micro-
controller. What value resistors would you use if the average current of the LEDs are 2 mA?
Draw the circuit diagram of your project.
16. Explain the different ways a button can be connected to a microcontroller input port. What
are the advantages of using the internal pull-up resistors? Explain how you can enable the
internal pull-up resistors of a PIC microcontroller.
17. Explain how a relay can be connected to the output port of a microcontroller. What are the
advantages and disadvantages of using relays?
3
PIC microcontroller project
development
In this chapter, we will look at the hardware and software tools required to develop PIC
microcontroller-based projects. We begin by looking at the minimum hardware tools required and
explain the function of each tool.
3.1 Required hardware tools
A PIC microcontroller is an integrated circuit and as such it is useless unless it is programmed and
used properly in an electronic circuit to carry out a certain task. The following hardware tools are
normally required before a microcontroller-based project can be developed:
• A desktop or a laptop PC
• PIC microcontroller programmer device
• A solderless breadboard or a similar circuit development board
• PIC microcontroller chip(s) and support components
• Power supply
We shall look at each of these tools in detail now.
3. 1. 1 PC
One of the most important and perhaps the most expensive tools we need is a PC. This can be a
desktop PC or a laptop PC. A laptop PC is preferred as it can be carried around and it provides
greater flexibility. The PC must be running one of the current Windows operating systems (e.g.
Windows 2000 or Windows XP) and it should be equipped with:
• Hard disk with several Giga-byte free space
• CDROM reader
• Floppy drive
• USB port (see notes in later sections)
• Parallel port (see notes in later sections)
Among other things, such as perhaps the Microsoft Office, Internet Explorer, Games, etc., the
hard disk will be required to store:
• A text editor software to develop our programs with
• The PicBasic compiler software
50 PIC BASIC projects
• PIC microcontroller programmer software
• The programs that we develop
Most of the commercial software is nowadays distributed on CDROMs and this is why you will
need a CDROM reader on your PC. You will find that some small software may still be distrib-
uted on floppies and this is why you may also need a floppy drive.
As we shall see in later sections of this chapter, some microcontroller programmer devices are
designed to be interfaced to the parallel port (or the printer port) of the PC, while some newer
ones are designed for the USB interface. Depending on the type of programmer device you have,
you will need either a parallel port or a USB port on your PC. Most laptop PCs are nowadays
equipped with only USB ports. If your programmer requires a serial or a parallel port, you can
purchase a device to convert between a serial or a parallel interface and the USB.
3.1.2 PIC microcontroller programmer device
A microcontroller programmer device is a stand-alone unit usually with one or more ZIF (zero-
insertion-force) type sockets mounted on it. The device is connected to the PC using either a par-
allel (or sometimes a serial) cable or by the USB interface. The new programmer devices with the
USB interface do not require any external power supply as they are powered from the USB port
of the PC they are connected to. The older devices with serial or parallel interfaces require an
external mains adaptor for their operation. The size of the ZIF socket determines the types of
chips that can be programmed by the device. Some sockets are 40-pin which can be used to pro-
gram microcontrollers with 40, 24, 20, 18, and 8 pins. Some programmer devices have sockets
with only 18 pins and they are designed to program smaller microcontrollers with 18 or less pins.
Figure 3.1 shows a typical PIC microcontroller programmer device based on a USB -type inter-
face. This device is distributed by Forest Electronics Ltd. in UK (website www.fored.co.uk) and
is known as the FED Programmer. The programmer has a single 40-pin ZIF socket mounted on
it. Microcontrollers with 40-pins (e.g. PIC16F877) can be programmed by placing them directly
on the socket and closing the handle. Devices with less number of pins (e.g. PIC16F84) are nor-
mally placed at the far end of the socket near the handle. The Programmer in Figure 3.1 has the
advantage that it can program a very large variety of PIC microcontroller chips. The programmer
device is sold for around £99 in UK and includes a USB cable.
A PIC microcontroller programmer device designed to operate with the parallel port is shown in
Figure 3.2. This particular device is known as the EPIC Plus programmer and it can be purchased
from the developers of the PicBasic/Pro compilers (microEngineering Labs Inc.) or from many
other electronic component distributors. EPIC Plus is a low-cost programmer with an 18-pin
socket on the device. There is no ZIF socket on the device and a standard DIL (dual-in-line)
socket is provided. The programmer is connected to the parallel port (the printer port) of a PC
using a 25-way DB25 type cable. If the parallel port of your PC is connected to the printer, the
PIC microcontroller project development 5 1
Figure 3.1 USB port-based PIC microcontroller programmer device
Figure 3.2 Parallel port-based PIC microcontroller programmer device
printer must be disconnected while you are using the programmer. EPIC Plus is powered from a
12-15 V DC mains adaptor.
Some microcontroller programmer devices have multiple ZIF sockets, also called gang program-
mers. These programmers are usually used to copy the same program to a number of devices at
52 PIC BASIC projects
the same time, such as during the production runs. An example multiple socket programmer is
shown in Figure 3.3.
Figure 3.3 Multiple socket programmer (Courtesy of Dataman)
3.1.3 Solderless breadboard
When we are building an electronic circuit, we have to connect the components as outlined in the
given circuit diagram. This task can usually be carried out on a strip-board or a printed circuit
board (PCB) by soldering the components together. The PCB approach is used for circuits which
have been tested and which function as desired and also when the circuit is to be made permanent.
It is not economical to use a PCB for one or only a few applications.
During the development stage of an electronic circuit, it may not be known in advance whether or not
the circuit will function correctly when assembled. A solderless breadboard is then usually used to
assemble the circuit components together. A typical breadboard is shown in Figure 3.4. The board
consists of rows and columns of holes that are spaced so that integrated circuits and other components
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Figure 3.4 A typical breadboard layout
PIC microcontroller project development 53
can be fitted inside them. The holes have spring actions so that the component leads can be held
tightly inside the holes. There are various types and sizes of breadboards depending on the complex-
ity of the circuit to be built. The boards can be stacked together to make larger boards for very com-
plex circuits. Figure 3.5 shows the internal connection layout of the breadboard given in Figure 3.4.
The top and bottom half parts of the breadboard are separate with no connection between them.
Columns 1 to 20 in rows A to F are connected to each other on a column basis. Similarly, rows G to
L in columns 1 to 20 are connected to each other on a column basis. Integrated circuits are placed
such that the legs on one side are on the top half of the breadboard, and the legs on the other side of
the circuit are on the bottom half of the breadboard. The first two columns on the left of the board
are usually reserved for the power and earth connections. Connections between the components are
usually carried out by using stranded (or solid) wires plugged inside the holes to be connected.
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Figure 3.6 shows the picture of a breadboard with two integrated circuits and a number of resis-
tors and capacitors placed on it.
The nice thing about the breadboard design is that the circuit can be modified very easily and
quickly and different ideas can be tested without having to solder any components. The components
can easily be removed and the breadboard can be used for other projects after the circuit has been
tested and working satisfactorily.
3.1.4 PIC microcontroller and minimum support components
A PIC microcontroller, even though it may have been programmed, is not of much use unless it is
supported by a number of components, such as the timing components and the reset circuitry.
As described in Chapter 2, a PIC microcontroller requires an external clock circuit (some PIC
54 PIC BASIC projects
Figure 3.6 Picture of a breadboard with some components
microcontrollers have built-in clock circuits) to function accurately. For accurate timing applica-
tions, the clock circuitry consists of a crystal, and two small capacitors. The commonly used crys-
tal frequency is 4-MHz and as described in Chapter 2, the capacitors for this crystal should be
around 22 pF. Figure 3.7 shows a 4-MHz crystal with two 22-pF capacitors.
Figure 3.7 A 4 MHz crystal with two 22-pF capacitors
Figure 3.8 shows the circuit diagram of a PIC microcontroller with a 4 -MHz crystal clock circuit.
The crystal and the capacitors are connected to the OSC1 and OSC2 inputs of the microcontroller.
PIC microcontroller project development 55
PIC16F84 microcontroller is taken as an example in all of the figures in this section, but the same
principles apply to all the other members of the PIC microcontroller family.
PIC
microcontroller
OSC1
OSC2
16 15
ci = ^l'-'l Z- C2
22p?T 4 MHz T~22pF
Figure 3.8 PIC microcontroller clock circuit
Resonators are more often used in microcontroller clock circuits because of their low cost, sim-
plicity, and low component count. Figure 3.9 shows some typical 3-terminal resonators, and the
connection of a resonator to a PIC microcontroller is shown in Figure 3.10. The centre pin is con-
nected to ground, and the two pins at either sides of the resonator are connected to the OSC1 and
OSC2 oscillator inputs of the PIC microcontroller.
Figure 3.9 Some typical resonators
A PIC microcontroller starts executing the user program from address of the program memory
when power is applied to the chip. As shown in Figure 3.11, the reset input (MCLR) of the micro-
controller is usually connected to the + V supply voltage through a 4.7K resistor.
56 PIC BASIC projects
PIC
microcontroller
OSC1 OSC2
16
15
Resonator
Figure 3.10 Using a resonator in a PIC microcontroller
4.7K
14
+5V
Vdd
MCLR
PIC
microcontroller
Figure 3.11 Connecting the reset (MCLR) input
There are many applications where the user may want to force reset action e.g. by pressing an
external button so that the program re-starts to execute from the beginning. External reset is very
useful during microcontroller-based system development and testing. Figure 3.12 shows how an
external reset button can be connected to a PIC microcontroller. Normally the MCLR input is at
Push to
reset
+5V
14
Vdd
47K IL
MCLR
flf
PIC
1
microcontroller
Figure 3.12 Applying external reset to the PIC microcontroller
PIC microcontroller project development 57
logic 1, and goes to logic which resets the microcontroller when the reset button is pressed. The
microcontroller goes back to the normal operating mode when the button is released.
Now that we have described the clock and the reset circuitry let us look at the design of a minimum
PIC microcontroller system. Figure 3.13 shows the circuit diagram of a PIC microcontroller circuit
with a 4-MHz resonator and an external reset button. As mentioned earlier, PIC16F84 microcontroller
is taken as an example in this figure. The layout of the circuit on a breadboard is shown in Figure 3.14.
+5V
4.7K
Push to
reset
Figure 3.13 Minimum PIC16F84 resonator-based microcontroller circuit
Reset button
4.7K resistor
PIC16F84
Resonator +5 V rail GND rail
Figure 3.14 Layout of the circuit in Figure 3.13 on a breadboard
58 PIC BASIC projects
3.1.5 Power supply
Every electronic circuit requires a power supply to operate. The required power can either be pro-
vided from a battery, or the mains voltage can be used and then reduced to the required level before
it is used in the circuit (e.g. a mains adaptor). In this section, we shall look at the design of a power
supply circuit to power our PIC microcontroller circuits using a battery as the source of power.
PIC microcontrollers can operate from a power supply voltage in the range 2 to 6 V. The standard
power supply voltage in digital electronic circuits is + 5 V and this is the voltage with which the
PIC microcontrollers are mostly operated. Unfortunately, it is not possible to obtain 5 V using
standard alkaline batteries only. The nearest we can get is by using three batteries, which gives
4.5 V and this is not enough to power standard logic circuits. In this section, we shall see how to
convert a standard 9-V battery (e.g. type PP3) voltage to 5 V so that it can be used in our PIC
microcontroller-based projects.
The simplest solution to drop the voltage from 9 to 5 V is by using a potential divider circuit using
two resistors. Although a potential divider circuit is simple, it has the major disadvantage that the
voltage at the output depends on the current drawn from the circuit. As a result of this, the output
voltage will change as we add or remove components from our circuit. Also, the output voltage
falls as the battery is used.
A voltage regulator circuit is needed to convert the 9 V battery voltage into 5 V, independent of the
current drawn from the supply. A basic voltage regulator circuit consists of a regulator integrated
circuit and filter capacitors. Figure 3.15 shows a low-cost voltage regulator circuit using the
78L05-type voltage regulator IC, and two filter capacitors. 78L05 (see Figure 3.16) is a 3-pin IC
with a maximum current capacity of 100 mA.
1
3
1 1
/OL-UU
9V 7
0.33 |jF =
battery i
2
p0.01[
>+5V
i>GND
3 2 1
OOO
78L05 bottom view
Figure 3.15 Circuit diagram of the +5-V voltage regulator
One of the pins of 78L05 is connected to the + V terminal of the battery in parallel with a 0.33-(xF
capacitor. One of the pins is connected to the —V terminal of the battery. The third pin provides
the +5 V output and a 0.01-|xF capacitor should be used in parallel with this pin. In applications
where a larger current is required, the 7805 regulator IC can be used. This is pin compatible with
PIC microcontroller project development 59
Output GND
(3) (2)
Input
(1)
Figure 3.16 78L05 voltage regulator
the low-power 78L05 and it has a maximum current capacity of 1 A. 78L05 should be used with
a suitable heatsink in applications drawing more than a few hundreds of milliamperes.
The complete circuit diagram of our PIC16F84-based basic system, together with the power sup-
ply, is shown in Figure 3.17. The layout of the circuit on a breadboard is given in Figure 3. 18. The
circuit in Figure 3.17 is our basic PIC16F84 microcontroller circuit and is now fully functional.
What is required now is to write our program and load it into the program memory of the micro-
controller. This is the topic of the next chapter.
9V
battery
Figure 3.17 Circuit diagram of the complete PIC16F84-based system
60 PIC BASIC projects
78L05 0.01 uF 0.33 uF
Figure 3.18 Breadboard layout of the system
3.2 Required software tools
All microcontrollers require a program (or software) for their operation. This program is developed
and tested by the programmer (or the user). The following software tools are normally required in
a PIC microcontroller-based project development cycle:
• A text editor
• PicBasic or PicBasic Pro compilers
• PIC programmer device software
We shall look at each of these tools in detail now.
3.2. 1 Text editor
A text editor helps us write our program (or the source code) so that it can be compiled and loaded
into our target microcontroller. There are two text editors readily available on any standard PC - the
Windows-based Notepad, and the DOS -based EDIT (note that WORD cannot be used as a text edi-
tor since it inserts special control characters into the text). We can use any of these text editors to
create a file and write our programs. A program file consists of a file name and a file extension.
The file name can be given any name, but the file extension is usually chosen as .BAS in PicBasic
and PicBasic Pro programs, for example, MYPROG.BAS and LED.BAS (In general, a program file
can be given any other file extension but when the program file is specified when invoking the
PicBasic or PicBasic Pro compilers, the file name and file extension must be specified to the com-
piler. If the file extension .BAS is used, then only the file name needs to be specified). It is a good
PIC microcontroller project development 6 1
practice to store all of our program files inside a folder so that we can find them easily when we
need them.
DOS edit
This is the old PC text editor which runs under the DOS operating system. Although not very
powerful, it should be powerful enough to develop small programs. As an example, to create a text
file called LED.BAS using the DOS editor the steps to follow are:
• Go to the MSDOS prompt. On Windows 2000 and XP machines this is usually found by fol-
lowing the path START -> Programs -> Accessories -> Command Prompt. You should then
go to the root directory C:\> by entering the commands CD .. followed by CD ..
• Go to the folder where you want to create your file. If the folder does not exist, create it using
the command MD followed by the required folder name. For example, to create the folder
named MYBASIC, enter the command MD MYBASIC. Then move to this folder by entering
the DOS command CD MYBASIC. You should see the DOS prompt C:\MYBASIC> as shown
in Figure 3.19.
• Start the DOS editor by entering the command EDIT LED.BAS. Write your program using the
PicBasic/Pro commands as explained in Chapter 4 and then save the program by pressing the
keys Alt F and then X and then press the RETURN key. Your program will be named LED.BAS
and will be saved inside the folder MYBASIC under the root directory.
™ Command Prompt
Minrnsnft UinrlnuR XP rUevs-inn h.1.2hHMI
<C> Copyright 1985-2001 Microsoft Corp.
C:\Docunents and Settings\ibrahimd>CD .
C:\Documents and Settings>CD ..
C:V>MD MVRARTC
C:\>CD MYBASIC
G-M1YBftSIC>_
'
n x
Figure 3.19 Creating the folder MYBASIC in DOS
WINDOWS notepad
Notepad is a powerful text editor which runs under all Windows operating systems. Notepad can
be accessed by following the path START -> Programs -> Accessories -> Notepad. You should
write your programs and then save them with the .BAS file extensions. It is important that when
you save the file you should select the Save As Type as All Files in the Notepad File save menu.
62 PIC BASIC projects
Although both Edit and Notepad are useful for creating new programs or for modifying an existing
program, Integrated Development Environments (IDE) such as the CodeDesigner and MicroCode
Studio provide a much easier and quicker method of program development since they combine a
powerful syntax highlighted editor with the compiler and the device programmer software. As a
result, the programmer can develop the program, compile it, and then load it into the target micro-
controller by using only one program interface. Both of these products are third-party products and
can be purchased from the developers, or in some cases, cut-down versions can be downloaded free
of charge from the Internet. We shall be looking at both products in the following sections.
CodeDesigner
The CodeDesigner software package has been developed by CSMicro Systems (web site www.
csmicrosystems.com). A cut-down version of the CodeDesigner, known as CodeDesigner Lite
can be downloaded free of charge from the microEngineering Labs Inc. web site (www.melabs.com).
The installation and configuration instructions are also available from their web site. After down-
loading the software, double click the cdlite icon and then follow the standard Windows installation
procedures. When the installation is finished, click the Finish button. The software is installed in
the root directory inside folder C:\CDLITE>. Now, create a shortcut to CodeDesigner Lite in your
desktop so that you can invoke the program easily. To do this, open the Windows Explorer and
navigate to My Computer -> Local Disk (C:) and click on Local Disk(C:). Then click on folder
CDLite. Find application cdlite on the right hand window and right click on the application. Then
select Send To -> Desktop (create shortcut). You will now have a shortcut named Shortcut to
cdlite in your desktop.
To start CodeDesigner, double-click on the shortcut you have just created. Figure 3.20 shows the
form you will see on your screen.
Sj CodeUesigner Lite - lC:\CUUte\Untitled1.pbpI
EJBle 6*t Compie Programmer Qpbons Wndow Heto
U & y & & % r Mm is *M n. | > | WC17C*
H
-Iff! x
<3Ffcs:2
-f
Lira 1 Cell
PBP
.;••
Figure 3.20 A typical screen form of the CodeDesigner Lite
PIC microcontroller project development 63
CodeDesigner Lite should be configured before it is used. Configuration involves specifying the
compiler and the programmer devices to be used in project development. To configure the com-
piler options, select Compile -> Compiler Options from the top menu. If you are using the
PicBasic compiler, specify the path to the compiler as shown in Figure 3.21 and press OK.
If you are using the PicBasic Pro compiler, specify the path to the compiler as shown in Figure 3.22.
Compiler Options
(PcBasic Compter
LOmptCf P^nfWW!
|C\FflC\PBQEXE
Command Lne Options.
U
QK
'J
frred
FndCompfci
I
F Auto Close Compiler Output Screen in 5 Sees
W Oonl Display DOS Window
=1
Figure 3.21 Configuring CodeDesigner Lite for the PicBasic compiler
Compiler Options
| PicBasic Pro Ccnptei
Compear PwfMJ(nei
Jd
Cancel
|C:\PBP\PBP.EXE
Command Line Options:
A
RndCompfei
1
P Auto Oose Compter Output Screen in
W Don"* Display DOS Window
5 Sees
-a
Figure 3.22 Configuring CodeDesigner Lite for the PicBasic Pro compiler
The CodeDesigner Lite software should then be configured for the PIC microcontroller pro-
grammer device you are using. To do this, select Programmer -> Programmer Options from the
top menu. You can now choose your programmer device from the given list. If your programmer
is not specified in the list, choose Other and specify the path to your programmer application soft-
ware. In this book, we shall be using the FED Programmer shown in Figure 3.1. Figure 3.23
Programmer Options
Cancel
Figure 3.23 Specifying the path to the FED Programmer
"3
| Other
Progiammei Pathname:
| C:\Ptogtam Fite*\F ED\Pie PfopammertReProfl _J
Command Line Options:
64 PIC BASIC projects
shows how to specify the path to this programmer inside the CodeDesigner Lite (if you are using
a different programmer device then you should either select your device from the list if it is avail-
able, or choose Other and enter the path to your programmer device software).
The CodeDesigner Lite is now ready for program development, compilation, and downloading
the code to the target PIC microcontroller. After writing our program, we can choose Compile ->
Compile from the top menu to compile our program. If the compilation is successful, we can
download our program to the programmer device by selecting the Programmer -> Launch
Programmer options from the top menu.
Note that when using the CodeDesigner software, the file extension of PicBasic programs should
be .PBC, and the file extension of PicBasic Pro programs should be .PBP.
We shall see a complete example, step-by-step in Section 3.4 on how to create a project from first
principles using the CodeDesigner Lite.
MicroCode studio
Although CodeDesigner Lite is sufficient for most of our project development tasks, we shall look
at MicroCode Studio, which is another popular IDE with In Circuit Debugging (ICD) capability,
designed specifically for the PicBasic and PicBasic Pro compilers. This IDE also provides a syntax-
highlighted editor to the programmer for easy program development. The IDE is interfaced to
PicBasic or PicBasic Pro compilers so that the user can easily and very quickly compile programs.
After the program is compiled with no errors, the compiled code can be sent to a PIC microcon-
troller programmer device to load the microcontroller. MicroCode Studio also provides an ICD
capability which enables the user to single-step the program in the target microcontroller in order to
examine and verify the operation of the program. The ICD is beyond the scope of this book and
interested readers are referred to the manufacturers' web site at www.mecanique.co.uk.
MicroCode Studio can be downloaded from the manufacturers' web site and it is available free
of charge to non-commercial users. The software is a cut-down version of the full product
MicroCode Studio Plus but it can be used in all of the projects developed in this book.
MicroCode Studio is also distributed free of charge and is installed as part of the PicBasic Pro
compiler demo package from microEngineering Labs Inc. As we shall see in the next section, this
package enables the user to create limited programs with a maximum line count of 3 1 (excluding
comment lines and blank lines), which should be enough to evaluate the compiler and to develop
many small to medium-size programs. After the installation, MicroCode Studio is invoked by
double clicking on its icon (or selecting it from the Programs menu) and the screen form shown
in Figure 3.24 is displayed when the program is invoked.
The software needs to be configured for the type of compiler, and the type of programmer we are
using. When the software is first invoked, it searches for the PicBasic compiler on the hard disk
and the compiler path is set automatically if the compiler is found. If the compiler is not found we
PIC microcontroller project development 65
i Microcode Studio - PICBASIC PRO (Untitled, tws)
0e £dt Jfew Ensj«t yef
J^H
<9 &i^£9aSia
■ .
16FS4
Code Explorer
£3 J UnfiTied
Q tndudes
Q Defines
tJ Var*ol«
|_J Akw«nd Mod fiers
_J Symbols
^) .abets
'*
MUM
Author
::■- :±?~
Sate
Version
roes*
UNTITLED. BAS
{select VISH. , u EDITOR OPTIONS J
Copyright (e) 2005 {select VIEW. . .EDITOR OPTIONS]
All Rights Reserved
03/09/2005
1,0
• ~r. ,.„,...,*....,.,.„..,.„,. ,.„....„, J...
Ready
J Ln 10 : Cd 55
Figure 3.24 MicroCode Studio screen form
can specify the path to the compiler by selecting View -> Compile and Program Options. Then
select the Compiler tab and specify the compiler path by clicking the Find Manually option. You
can also click the Find Automatically button to see if the compiler path can be found automat-
ically. The type of programmer device we are using should be configured by choosing View ->
Compile and Program Options and then clicking the Programmer Tab. Depending on the type of
programmer device we have, we can either choose the default one or choose Add New Programmer
to add our own programmer device. Figure 3.25 shows how the FED Programmer device can be
selected to be the default programmer.
We can now write our program and when finished, compile it by selecting Project -> Compile or
we can send the code to a PIC programmer by selecting Project -> Program.
3.2.2 PicBasic and PicBasic Pro compilers
These compilers are distributed on a floppy diskette or on a CDROM and they should be installed
before they can be used. The installation is very easy - insert the diskette into drive A and click
START -> Run and type A:\INSTALL in the RUN dialoug box. The compiler files will automat-
ically be loaded onto the hard disk. PIC Basic files are loaded inside the folder
C:\> PBC
66 PIC BASIC projects
Compile and Program Options
CompJer I Assembler Programmer
Default Programmer FED Programmer
Ed I..
Add New Programmer. . . Remove Programmer Entry
□ insert source file comments
L«s ting file
G Generate listing, symbol table and map ffe
OK
J | Help
Figure 3.25 Adding the FED Programmer device
And the PIC Basic Pro files are loaded inside the folder
C:\> PBP
You may look at the files in these directories by using your Windows Explorer program.
The compilers can either be activated directly from DOS, or by using CodeDesigner or the MicroCode
Studio as described in Section 3.2.1.
To activate the compilers directly from DOS, go to the Command Prompt mode and then enter
C:\PBO PBC -pxxx my file for PicBasic compiler
and
C:\PB P> PBP -pxxxx my file for PicBasic Pro compiler
where
-pxxx is the PIC microcontroller type (e.g. -pl6F877 for PIC16F877). If the microcon-
troller type is not specified, the default PIC16F84 is assumed;
-my file is the name of the program to be compiled (a .BAS file extension is assumed).
For example, the following command assumes that we are using a PIC16F627 microcontroller,
and compiles PicBasic Pro file called LED. BAS. The file is assumed to be in the same directory
as the compiler:
C:\PBP> PBP -pl6F627 LED
Similarly, the following command can be used to compile a program called MOTOR. BAS using
the PicBasic compiler. It is assumed here that our target system is a PIC16F84 microcontroller.
PIC microcontroller project development 67
C:\PBO PBC MOTOR
A demo version of the PicBasic Pro compiler is available from the web site of microEngineering
Labs Inc. and this is included on the CDROM distributed with this book. You can use this demo
version to create programs with up to 3 1 lines long. The demo version also includes the MicroCode
Studio which can be installed during the installation of the compiler.
The compiler generates a number of files with the same filename but with different extensions
(for example, .ASM, .HEX etc). The file with the extension .HEX is also known as the object file
and this is the file which is to be sent to the programmer device.
3.2.3 Programmer device software
You should install the programmer software which has been distributed with your programmer device.
In this book, the USB -based FED Programmer device is used and the software for this device is
installed by following the standard Windows software installation procedures. The programmer soft-
ware is invoked automatically when working with CodeDesigner Lite or with the MicroCode Studio.
Figure 3.26 shows the typical screen form of the FED Programmer software. First of all, you should
select the type of PIC microcontroller you will be using. To do this, click PIC from the top menu and
then click Select Device (see Figure 3.27) and select your microcontroller from the given list. The
device name you have chosen should appear at the bottom left-hand corner of the screen form.
C5 PIC Programmer -
YOL.HEX
niiBl
Ffc PIC
Options Hdp
& ea
v a n i
Fute«3FF5
000000 :
2878 0QA2
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: ; : :
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: . . .a". . .
000018 :
018E 1COC
008E
:■::: :r:
0822
068E
3001
: . . . . a ". .
00002Q :
008C 0180
oeoo
0522 060E
iros
0008
0A8C
■
000028 :
1903 OFeD
2822
0008 3AFF
1784
0560
2873
; . . • . « . . a
000030 :
018F oooe
3GFF
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000038 :
3003 00SD
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000070 :
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01 6F 300D
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20S7 1D03
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30A0 00&C
01BD
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: W.<
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EEPF
00 : FF
FF FF FF FF FF
"F FF : .
A
OS : FF
FF FF FF FF FF
T FF : .
10 : FF
FF FF FF FF FF
T FF : .
4 . . .
18 ; IT
FF FF FF FF FF
T FF : .
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20 : FF rr FF FF FF IT
r uwicsp
rF FF : .
....
.
V
9
o o
1&F84 CS-A0CE U*« FFFF Count:
8 Session
Figure 3.26 FED Programmer screen form
68 PIC BASIC projects
[3 PIC Programmer YOL.HEX
S>
Fun
go3
: ::.
: : : .
J L L .
000
000
000
000
000
: : : .
ooot
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000078
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Options Hdp
Read
gank Check
ttenfy
Checksum PIC
H
Pi
FS
F7
Program Entire Device F2
Program Config Flhcs F8
Program yser ID F9
Program EE Data F10
E/ase EEPROM F3
Verrfy After Write
Qukfc Program Made
Select Device
Ctri+V
Ctrl-KJ
SODS
1903
U83
008C
00A9
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3E01
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20S7
0514
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-
EEPROM Date
00 t FF FF FF FF FF FF FF FF
08 : FF FF FF FF FF FF FF FF
10 : FF FF FF FF FF FF FF FF
U : FF FF FF FF FF FF FF FF
20 : FF FF FT FF FF FT FF FF
T UselCSP
-
V
9
16F84 CS=A0CE Use* - FFFF Count : Session :
Figure 3.27 Selecting a PIC microcontroller
Insert the PIC microcontroller chip into the socket and close the handle. Then, click File and then
Open to open the compiled .HEX file of your program. Click File and then Fuses to set the PIC
microcontroller configuration fuses for the power-up timer option, watchdog option, and the timing
device used. You should normally click only the crystal (XT) option as shown in Figure 3.28. You
Fuse value 3FF9H
r Code Protect
I - Power Up Timer
r rWatchDod
r rc
r hs
I? XT
TLP
Cancel
Clear Fuses
Heip
Figure 3.28 Setting the configuration fuses
PIC microcontroller project development 69
can now program the configuration fuses by selecting PIC followed by Program Config Fuses. The
microcontroller can then be programmed by selecting PIC followed by Program Entire Device.
3.3 Bundled development systems
Some manufacturers provide bundled packages of their hardware and software products mainly
for development and experimenting purposes. Bundled packages have the following advantages:
• The cost is lower than the cost of purchasing the individual products in the package.
• They usually contain all the necessary hardware for developing microcontroller-based products.
• They usually contain the compiler software and programmer software to enable the user develop
projects easily.
Some bundled packages for PIC microcontrollers, including the PicBasic or PicBasic Pro compilers
are described in this section. All of the bundled products given in this section are manufactured by
microEngineering Labs Inc. Further information can be obtained from their web site www.melabs.com
Developer's bundle
This is a complete PIC microcontroller project development package and as shown in Figure 3.29,
the package contains
• PicBasic Pro compiler
• Melabs serial programmer device
• LAB -XI Experimenter board
• PIC microcontroller chips
• All the necessary mains adaptors and interface cables
Figure 3.29 Developer's Bundle (Courtesy of microEngineering Labs Inc.)
PicBasic compiler bundle
This package is based on the PicBasic compiler. The package contains (see Figure 3.30)
70 PIC BASIC projects
PicBasic compiler
EPIC Plus programmer
PICPROT018 Experimenter board
PIC microcontroller chips
All the necessary mains adaptors and interface cables
-#
Figure 3.30 PicBasic Compiler Bundle (Courtesy of microEngineering Labs Inc.)
LAB-X1 bundle with serial programmer
This bundle is for those people who have the PicBasic or the PicBasic Pro compilers and are look-
ing for a programmer device and an experimenter board. The package contains (see Figure 3.31)
• LAB -XI Experimenter board
• Melabs serial programmer
• PIC microcontroller chips
• All the necessary mains adaptors and interface cables
Fig. 3.31 LAB-X1 Bundle with serial programmer (Courtesy of microEngineering Labs Inc.)
PicBasic or the PicBasic Pro compilers can be added to the bundle at a reduced cost.
PIC microcontroller project development 7 1
3.4 Experimenter boards
In Section 3.1.3, we have seen how to use a solderless breadboard to develop microcontroller-
based projects easily and also at low cost. Some manufacturers provide experimenter boards for
the development and testing of microcontroller-based systems. Some low-cost experimenter
boards contain LEDs and push-button switches. Some more expensive ones may contain LCD
displays, keyboards, serial input/output ports, relays, on-board chip programmers, and so on.
Examples of some popular experimenter boards are given below.
LAB-X1 experimenter board
This board is manufactured by the microEngineering Labs Inc. Some of the features of this board
are (see Figure 3.32)
• A keypad with 16 switches
• Potentiometers, IR, real-time clock
• LED bargraph
• LCD module
• RC servo connectors
• Speaker
• RS232 and RS485 interface
• Serial EEPROM
• Prototyping area
• 5-V regulator
Figure 3.32 LAB-X1 Experimenter board (Courtesy of microEngineering Labs Inc.)
The company also manufactures other experimenter boards such as LAB-X2, LAB-X3, LAB-X4,
and so on.
72 PIC BASIC projects
PIC microcontroller training and development kit
This board is manufactured by Kanda Systems Ltd. Some of the features of the board are (see Fig.
3.33)
• A/D converters
• RS232 interface
• 4-digit, 7-segment display
• LED bar-graph
• 8 push-button switches
• Piezo-buzzer
• Infrared transmitter-receiver
• Sockets for serial EEPROM
Figure 3.33 Kanda System's Development kit (Courtesy of www.kanda.com)
EasyPIC 2 development system
This is a very sophisticated development board manufactured by MikroElektronika. The board sup-
ports 8, 14, 18, 28, and 40-pin PIC microcontrollers. Some of the important features of the board are
(see Figure 3.34)
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Figure 3.34 EasyPIC 2 Development system (Courtesy of MikroElektronika)
PIC microcontroller project development 73
• RS232 interface
• 4-digit, 7-segment display
• 32 push-buttons
• Digital thermometer
• 32LEDs
• A/D converters
• 2 potentiometers
• On board USB programmer
3.5 Example project development
In this chapter, we have seen the hardware and software tools required to develop a PIC
microcontroller-based project. We shall now summarise the steps required for the development of
a project by giving a simple example.
In this example, we shall connect a small LED to port RB7 (bit 7 of PORTB) of a PIC16F84
microcontroller and then write a program to continuously flash the LED with 1-s intervals; i.e. the
LED will be ON for 1 s, then OFF for 1 s, then ON again for 1 s, and so on. You may have difficulty in
understanding the operation of the program given in this section as you may have not read Chapter 4
yet. You should not worry about the details of the actual program since this exercise is not designed
to teach you programming, but to show you the steps required for a typical project development cycle.
Step 1 - design the circuit
The circuit diagram of the project is shown in Figure 3.35. A small LED is connected to port RB7 (pin
number 13) of a PIC16F84 microcontroller through a current-limiting resistor. The voltage across an
LED is about 2 V, and the average current through an LED depends on the type of LED we are using,
but we can assume a current of about 10 mA. If we assume that the voltage at the output of an output
pin is 5 V, the value of the required current-limiting resistor is then found as
5 - 2 V 3 V
R = — = -?-— = 0.3K
10 mA 10 mA
0.3K is not a standard resistor and we can choose the resistor as 330 O which will give slightly
less than 10 mA through the LED.
The microcontroller is operated from a 4-MHz resonator and an external reset button is connected
as described in Section 3.1.4. A 9-V battery together with a voltage regulator circuit is used to
power the microcontroller as shown in Section 3.1.5.
Step 2 - required components
Make a list of the required components:
• Solderless breadboard
• PIC 1 6F84 microcontroller
74 PIC BASIC projects
4 -MHz resonator
Push-button switch
4.7K resistor
LED
330-fl resistor
78L05 regulator
0.33-(jlF capacitor
0.01-(jlF capacitor
9-V battery clip
9-V battery
9V ! 0.33pF = =
battery , ^
78L05
,o ^ 330
1 %=
LED
Figure 3.35 Circuit diagram of the project
Step 3 - construct the circuit
Figure 3.36 shows the circuit constructed on a solderless breadboard. You should connect the bat-
tery and make the following checks before inserting the microcontroller in its place. A voltmeter
(e.g. a digital test meter) will be required for these checks.
• Inspect the breadboard visually to make sure that all the connections are correct.
• Measure the voltage at the +5 V rail and make sure that the voltage is very close to +5 V. You
should check your battery connections and the 78L05 regulator connections if the voltage is
not close to +5 V. You should not continue with the project unless you get the correct voltage
at this step.
• Measure the voltage at pin position 14 of the PIC microcontroller chip. Again, this voltage
must be very close to +5 V and you should not continue until you get the correct voltage.
• Disconnect the battery
You can now insert the microcontroller chip in its place, but wait until after the chip is programmed.
PIC microcontroller project development 75
Figure 3.36 Project constructed on a breadboard
Step 4 - write the program
Before writing our program, let us assume that we shall be keeping all of our programs in a folder
named MYPROGS under the root directory. To do this, the following steps will be required (this
task will have to be done only once):
• Start the Windows Explorer and click on My Computer. Then click on Local Disk (C:). Click
on File in top menu and then select New -> Folder. Enter the name of the new folder as
MYPROGS and press the RETURN key. The new folder has now been created and you may
Exit the Windows Explorer.
At this part of the development, we shall assume that we are using the PIC Basic Pro compiler.
Double-click the CodeDesigner icon in the Desktop to start the program and make sure that the
Compiler Option chosen is the PicBasic Pro.
Select the microcontroller type as PIC 16F84 by clicking on the top middle part of the form, left
of the Files: 1.
Write your program by entering the statements shown in Figure 3.37.
Click on File in the top menu and save your program with the name MYLED in the folder
MYPROGS (note that the file extension is chosen as .PBP automatically).
Compile the program by selecting Compile from the top menu and then click on Compile.
Make sure that there are no errors in the compilation.
Connect the programmer device to your PC and insert a PIC16F84 chip into the programmer
device. Click on Programmer in the top menu and select Launch Programmer. You should now
see the programmer software on your screen. Click on PIC in the top menu and select the
device type as PIC16F84.
76 PIC BASIC projects
SI CodeDesigner Lite - [C:\MYPROGS\MYLED, pbp]
l & I Rip Rit fompflp Prri(jranm*»r Qphnrr: Wjndnw Help
-Jglxl
d & y a x %
A tFtp
► ^
PIC16 c 3m
tgRksjl
LED FLASHING PROGRAM
In this program an LED is connected to port pin RB7 of
a PIC16F84 microcontroller. The microcontroller is
operated tram a 4MHz resonator. The program t lashes the
LED with 1 second intervals i.e. 1 second OH. 1 second
OFF. then aqain 1 second OK, and so on.
Programmer : D. Ibrahim
Date : August 200S
File : HTTLED.PBP
Loop :
High PORTB
Pause 1UUU
low PORTB
Pause
GoTo Loop
End
LED = OH
Wait 1 second
LED = OFF
Wait 1 second
repeat forever
End o£ program
J I
j*
Line 1 Coil
A
Figure 3.37 The program of our project
• Click on File in the top menu and select Open. Navigate to folder MYPROGS and click on file
MYLED. Click on OPEN to load the object file of your program (MYLED.HEX) to the pro-
grammer memory (see Figure 3.38).
S PIC Programmer MYLED.HEX
Fie PIC Qpoons j^dp
i3t3
Fuxe-3FF5
000000
::::::
000010
000018
000020
000028
000030
000038
000040
:■■:■::•;:
::::::
: : : : e:
: :::•:
000068
: : : : - :
: ::;~:
000080
000088
000090
000098
0000AQ
9O00U
2£*3
008C
07 £C
0000
1786
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2828
3FFF
3FFF
3FFF
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3FFF
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3FFT
3FFF
3FFF
3FFF
3 DO 3
09eD
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2822
i6e3
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0063
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3FFF
177:
Sill
3FFF
3FFF
3 IFF
777
3FFF
3rFF
3FFF
3FFF
3FFF
3QFC
:fm
0008
1386
1386
2839
3FFF
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3FFF
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3FFF
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: rr?
3FFF
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1C03
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If!!
3FFF
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2803 018D
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281E 1C8C
1283 0064
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3FFF 3FFF
3FFF 3FFF
3FFF 3FFF
3FFF 3FFF
3FFF 3FFF
3FFF 3FFF
3FFF 3FFF
3FFF 3FFF
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3FFF 3FFF
3FFF 3FFF
3FFF 3FFF
3FFF 3FFF
3FFF 3FFF
3FFF 3FFF
-II;
2815
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2002
2002
3FFF
3FFF
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::::
3FFF
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1777
WW
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I.
..h
EEFflOM Date
00 : FF FF FF FF FF FF FF FF
08 : FF FF FT FF FF FF FF FF
10 : FF FF FF FF FF FF FF FF
18 : FT FF FT FF FF FF FF FT
20 : FF FF FF FF FF FT FF FF ; . , « .
r usdcsp
16F84 CS=156D Usei - FFFF Count : 3 Session :
*
Figure 3.38 Programmer form
PIC microcontroller project development 11
Click on File in the top menu and select Fuses. In this form, tick only the XT box to indicate
that we are using a crystal for timing.
Click on PIC in the top menu and select Program Config_Fuses to program the configuration
fuses. You should get a confirmation when the configuration fuses have been programmed.
Click on PIC in the top menu and select Program Entire Device. Wait until the chip is pro-
grammed. You should get a confirmation when the device has been programmed.
Remove the chip from the programmer and place it on the breadboard. Connect the battery and
test your project. The LED should be flashing with 1-s intervals. If the project is not working,
first check the hardware to make sure that the connections are correct. Then check the software.
3.6 Other useful development tools
In addition to the microcontroller hardware and software development tools described in this
chapter, there are some other development tools which could be very useful during the project
development cycle. Two of such tools are described briefly in this section.
3.6.1 Simulators
A simulator is a software development tool designed to run on the PC. A simulator enables the
programmer (or the user) to test the functional operation of a program on the PC, without having
to construct any microcontroller-based hardware.
Typically, the programmer develops the program and then compiles it. The simulator program is
then invoked and the object code of the program is loaded into the simulator program (some simu-
lators have built-in compilers or assemblers which make it easier to write a program, compile it and
then simulate using the same development tool). The programmer can then single- step through the
program and observe the values of variables as they change. Some simulators provide input-output
ports where the programmer can connect various software-simulated devices such as LEDs, 7-segment
displays, LCDs, motors, and so on. The programmer is also allowed to change the values of variables
during a simulation session so that the operation of the program can be analysed in detail and any
logic errors can be removed before the program is loaded into a microcontroller.
Although the simulators can be very useful development tools, they have the disadvantage that the
program is not run in real-time. Another disadvantage is that it is not possible to examine the oper-
ation of the program when real hardware devices are connected to the input-output ports. For
example, it is not possible to connect a real motor to the simulator and see it running. As a result
of this, any hardware-related timing errors cannot be detected by the simulation process.
3. 6.2 In Circuit Emulators (ICE)
This is another useful microcontroller development tool. In an ICE application, the microcontroller
of the target system is replaced by the ICE which behaves exactly same as the original microcon-
troller. Typically, the microcontroller is removed from its socket and replaced by the ICE header.
78 PIC BASIC projects
This header is usually connected to an emulator box which contains the main emulator functional-
ity. A PC is then connected to the emulator box. The ICE emulates the replaced microcontroller in
real-time as if the replaced microcontroller is in the socket. The programmer can load the program
he has developed into the emulator and can run, single-step, and trace the operation of the program.
Some emulators have advanced functions such as performance analysis, trace buffer, triggering
functions, and breakpoint features. Breakpoints give the programmer the ability to stop the pro-
gram at precise locations and then to examine the values of variables at these points.
A simpler, and also much cheaper type of emulator is an In Circuit Debugger (ICD). ICD provides
real-time emulation of the target processor. The program can be executed in single-step mode
with breakpoints. Memory locations and values of various registers can be examined in real-time.
3.7 Exercises
1 . Describe the minimum hardware tools required to develop PIC microcontroller-based projects.
2. Explain why a PC is needed to develop PIC microcontroller-based projects.
3. What is the function of a programmer device? What types of programmer devices are there?
4. Explain what a breadboard is and why it can be useful during microcontroller-based project
development. What are the advantages and disadvantages of using a breadboard?
5. Explain why a power supply is required to power a PIC microcontroller. Draw the circuit dia-
gram of a typical low-cost +5-V power supply.
6. Describe the minimum software tools required for the development of PIC microcontroller-
based projects.
7. Explain why you need a text editor. Give examples of at least two text editors available on
your PC.
8. Explain what the advantages of using an Integrated Development Environment (IDE) are.
Give an example of an IDE for the development of PIC microcontroller-based projects.
9. Explain what CodeDesigner is and the advantages of using it.
10. Explain the benefits of using the MicroCode Studio software package during the develop-
ment of PIC microcontroller projects.
11. Explain in detail the steps required to develop a simple PIC microcontroller-based project.
Can you suggest some methods to speed-up the development time?
12. Explain where and why you might need to use a simulator. What are the limitations of
simulators?
3.8 Links to useful web sites
Links to some useful web sites on PIC microcontrollers and development tools are listed in this
section.
microEngineering Labs Inc.
MikroElektronika
Kanda Systems Ltd.
www.melabs.com
w w w.mikroelektronika. co . y u
www.kanda.com
PIC microcontroller project development 79
Maplin Electronics
RS Components
Farnell In One
Mecanique
CSMicro Systems
Brunning Software
Microchip Technology Inc.
Images SI Inc.
Microcontroller Pros Corporation
ASIX
HVW Technologies Inc.
Microdesigns Inc.
Apogeekits
Quasar Electronics
Spectro Technologies Inc.
Dontronics
Hobby Engineering
Mouser
ProtoCessor
Crownhill Associates
www.maplin.co.uk
www.rswww.com
www.farnell.com
www.mechanique.co.uk
www.csmicrosystems.com
http://brunningsoftware.co.uk
www.microchip.com
www.imagesco.com
http://microcontrollershop.com
www.pic-tools.com
www.hvwtech.com
www.microdesignsinc.com
www.apogeekits.com
www.quasarelectronics.com
www.spectrotech.net
www.dontronics.com
www.hobbyengineering.com
w w w.mouser. com
www.protocessor.com
www.crownhill.co.uk
4
PicBasic and PicBasic Pro
programming
BASIC is one of the oldest and one of the easiest programming languages to learn. You should be
able to learn and program in BASIC in less than an hour. In this chapter, we shall be looking at
the principles of programming PIC microcontrollers using the PicBasic and PicBasic Pro lan-
guages. Both these languages are very similar to the standard BASIC language but they have
some modified and some additional instructions specifically for microcontroller programming.
Both PicBasic and PicBasic Pro languages have been developed by the microEngineering Labs
Inc. PicBasic is a lower-cost, simpler language than PicBasic Pro and it is aimed at students and
hobbyists. PicBasic Pro is more expensive, aimed at professionals, and includes additional com-
mands for more advanced instructions.
Table 4.1 gives a list of the comparison of PicBasic and PicBasic Pro languages. Before we pro-
ceed to the chapter on PIC applications and projects, we shall be looking at how we can program
the PIC microcontrollers using these languages.
4.1 PicBasic language
In this section, we shall be looking at the variable types and the commands of the PicBasic lan-
guage. A detailed description of all the commands can be found in the PicBasic Compiler man-
ual, available from the web site www.melabs.com, or a printed copy can be obtained from the
microEngineering Labs Inc.
4.1.1 PicBasic variables
Variables are used to store temporary data in a program. These variables are stored in the general-
purpose area of the RAM memory of a microcontroller.
Variables in PicBasic can be bytes (8 bits), or words (16 bits). Byte variables are named BO, Bl,
B3, etc., and word variables are named WO, Wl, W2, etc. Word variables are made up of two
bytes. For example, WO uses the same memory space as bytes BO and Bl. Similarly, Wl word
variable is made up of bytes B2 and B3, and so on. We can access the bit positions of variables BO
and Bl using predefined names BitO, Bitl,...,Bitl5. For example, the least significant bit of BO
PicBasic and PicBasic Pro programming 8 1
Table 4.1 Comparison of PicBasic and PicBasic Pro
PicBasic
PicBasic Pro
Low-cost ($99.95)
Higher cost ($249.95)
Limited to first 2 K of program space
No program space limit
Interrupt service routine in assembly language
Interrupt service routine can be in assembly
language or in PicBasic Pro
Peek and Poke used to access registers
Registers can be accessed directly by specifying
their names
Some commands can be used only for
PORTB, PORTC, or GPIO
Commands can be used for all ports
Clock speed 4 MHz
Any clock speed up to 40 MHz
Most 14-bit Pic microcontrollers supported
All PIC microcontrollers, including 12-bit ones
are supported
More code space in memory
5-10% less code space in memory
More difficult to learn and less powerful
Easier to learn and more powerful
No LCD commands
Special LCD control commands (LCDOUT,
LCDIN)
No hardware serial communication commands
Special hardware serial communications
commands (HSERIN, HSEROUT)
No PWM commands
Special PWM commands for the microcontrollers
that have built-in PWM circuit (HPWM)
No Select-Case command
Select-Case command for multi-way selection
No program memory read-write commands
Commands to read and write program memory
locations (READCODE, WRITECODE)
No One- wire device interface
One- wire device interface commands (OWIN,
OWOUT)
No USB commands
USB commands for microcontrollers that have
built-in USB circuits (USBIN, USBOUT)
No X-10 remote control commands
X-10 remote control commands (XIN, XOUT)
No A/D commands
A/D commands for microcontrollers that have
built-in A/D converters (ADCIN)
is labelled BitO, the second bit Bitl, and the most significant bit as Bit7. Similarly, the least
significant bit of B 1 can be named as Bit8, and the most significant bit of Bl as Bitl5.
Variables are stored in the RAM memory of a PIC microcontroller where BO is the first RAM
location, B 1 is the second RAM location, and so on. The size of the RAM memory depends on
the type of PIC microcontroller used and Table 4.2 gives a list of the variable names for various
microcontrollers. For example, if we are using a PIC16F84-type microcontroller, we can define
52 variables from BO to B51, and the highest variable name must not exceed B51. Note that you
can only access RAM locations up to the available RAM. For example, if you try to access a RAM
82 PIC BASIC projects
location that does not exist, the compiler does not generate an error and your program may not
work as expected.
Table 4.2 PicBasic variable names
Microcontroller
Variables (bytes)
Variables (words)
PIC16C61
B0-B21
W0-W10
P1C16C71
B0-B21
W0-W10
P1C16C710
B0-B21
W0-W10
P1C16F83
B0-B21
W0-W10
P1C16C84
B0-B21
W0-W10
P1C16F83
B0-B21
W0-W10
P1C12F629
B0-B47
W0-W23
P1C12F675
B0-B47
W0-W23
PIC16F630
B0-B47
W0-W23
PIC16F676
B0-B47
W0-W23
PIC16C711
B0-B51
W0-W25
PIC16F84
B0-B51
W0-W25
P1C16C554
B0-B63
W0-W31
P1C16C556
B0-B63
W0-W31
P1C16C620
B0-B63
W0-W31
PIC16C621
B0-B63
W0-W31
PIC 12C67X
B0-B79
W0-W39
P1C14C000
B0-B79
W0-W39
P1C16C558
B0-B79
W0-W39
P1C16C558
B0-B79
W0-W39
P1C16C622
B0-B79
W0-W39
PIC16C62
B0-B79
W0-W39
PIC16C63
B0-B79
W0-W39
PIC16C64
B0-B79
W0-W39
P1C16C65
B0-B79
W0-W39
P1C16C72
B0-B79
W0-W39
P1C16C73A
B0-B79
W0-W39
PIC16C74A
B0-B79
W0-W39
The relationships between the byte, word, and bit variables are given in Table 4.3. For example, word
W2 is made up of bytes B4 and B5. You will see additional predefined variables in Table 4.3, named
Port, Dirs, and Pins. Pins refers to the PORTB hardware, Dirs refers to the port data direction
register for PORTB, i.e. TRISB and a sets its associated Pin to an input, and a Dirs of 1 sets its
PicBasic and PicBasic Pro programming 83
associated Pin to an output. Port is a word variable that combines Pins and Dirs. The individual pins
of a port can be accessed by the variable names PinO, Pinl,. . . ,Pin7.
Table 4.3 Relationship between byte, word, and bit variables
Word variable
Byte variable
Bit variable
WO
BO
Bit7, Bit6,...BitO
Bl
Bitl5, Bitl4,...Bit8
Wl
B2
B3
W2
B4
B5
VV3
B6
B7
W39
B78
B79
Port
Pins
Pin7,Pin6,...PinO
Dirs
Dir7, Dir6,...DirO
Symbols
In order to make programs more readable, we can assign meaningful names to variables, instead
of using BO, B 1, etc. The PicBasic statement symbol is used for this purpose. For example, we can
assign variable name count to location BO with the instruction:
Symbol count = BO
Symbols must be declared at the top of a program. Symbols can also be used to assign constants
to names. For example, the following statement assigns the decimal value 20 to the name total.
Note that this statement does not occupy any location in the microcontroller RAM memory. The
number is simply represented with a name.
Symbol total = 20
Command names in PicBasic are case insensitive and can be written in upper case, lower case, or
with a mixture of the two. Thus, all the variables below are the same:
TOTAL
Total
toTal
84 PIC BASIC projects
Comments
Comments are useful in programs to describe the operation performed in a line or in a block of
lines. A comment starts with either the keyword REM or the single quote character ('). All the
characters following a comment character are ignored. Examples of comments are:
REM This is a simple test program
LOW ' Clear Pin to
HIGH 1 REM Set Pin 1 to 1
Numeric Values
In PicBasic, numeric values can be specified in three ways: decimal, binary, and hexadecimal.
Decimal values are the default and require no prefix. Binary values are specified using the prefix
"%" followed by the number. Hexadecimal values are specified using the prefix "$" followed by
the number. Some examples are:
REM A has the same value in all the following three statements
A = 10
A = %00001010
A = $0A
ASCII Values
Character constants can be converted into their ASCII values by enclosing them in double quotes.
Only one character must be specified. For example,
"A" ' ASCII value of decimal 65
" 1 " ' ASCII value of decimal 49
String Constants
Although PicBasic does not provide string-handling functions, we can define strings of characters
by enclosing them in double quotes. For example,
"COMPUTER"
The above string is treated as a string of ASCII characters with values "C", "O", "M", "P", "U",
«rpjj "TIJ" ""D"
Line Labels
In PicBasic programs, we often want to jump to different parts of a program, or to jump to a sub-
routine. A line in PicBasic is referred by a line label. A line label can be a valid identifier (a valid
name in PicBasic), followed by a colon character (:). For example,
LOOP:
Multi-statement Lines
It is possible to use more than one statement on a line to make the program more readable. A colon (:)
character should be used to separate more than one statement in a line. The size of the code does
PicBasic and PicBasic Pro programming 85
not change when more than one statement is written on the same line. For example, consider the
following statements:
B0 = 3
Bl =5
B2 = 8
The above statements can all be written on the same line as
BO = 3 : Bl = 5 : B2 = 8
4. 1.2 PicBasic mathematical and logical operations
PicBasic supports a number of mathematical and logical functions which make calculations easy
in programs. The operations are performed on integer numbers only with 16-bit precision and
there is no floating-point number format. Also, all math operations are performed strictly from
left to right. The operators supported are
+
addition
—
subtraction
*
multiplication
**
most significant bit (MSB) of multiplication
/
division
//
remainder in a division
MIN
limit to minimum value
MAX
limit to maximum value
&
bitwise AND
1
bitwise OR
A
bitwise XOR
&/
bitwise AND NOT
1/
bitwise OR NOT
A /
bitwise XOR NOT
Multiplication is done on 16 X 16 bit numbers, resulting in a 32-bit result. The "*" operator returns
the lower 16-bits of the 32-bit result. Similarly, the "**" operator returns the upper 16-bits of the
result. For example,
W2 = Wl * WO ' Multiply Wl with WO. The lower 16-bits of the result
' are placed in W2
or,
or,
W2 = Wl ** WO ' Multiply Wl with WO. The upper 16-bits of the result
' are placed in W2
W2 = Wl * 100 ' Multiply Wl with 100. Place the lower 16-bits of the
' result in W2. Note that this is the multiplication
' found in most programming languages
86 PIC BASIC projects
Similarly with division,
W2 = Wl / WO ' Divide Wl by WO. The result is placed in W2
or,
W2 = Wl // WO ' Divide Wl by WO. The remainder is placed in W2
MIN is used to limit the result to the minimum value defined. For example,
Bl = BO MIN 100
Sets Bl to the smaller of BO and 100, i.e. Bl cannot be greater than 100.
Similarly, MAX is used to limit the result to the maximum value defined. For example,
Bl = B0 MAX 100
sets Bl to the larger of B0 and 100, i.e. Bl will be between 100 and 255.
Bitwise logical operations operate on the entire byte and these operations can be used to extract
bits from bytes or to set and clear bits of a byte. For example, to extract the least significant bit of
B0 we can write
B0 = B0 & %00000001
Similarly, to set bit 2 of B 1 to be 1 we can write
Bl =B1 l%00000100
To store the upper four bits of B 2 in B 1 we can write
Bl =B2&%11110000
4.1.3 PicBasic program flow control commands
Program flow control commands are important in every programming language since they enable
the programmer to make a decision and change the flow of the program based on this decision.
PicBasic language supports the following program flow control commands:
BRANCH
BUTTON
CALL
FOR... NEXT
GOSUB... RETURN
GOTO
IF... THEN
PicBasic and PicBasic Pro programming 87
We shall now see what the functions of these commands are and how to use them in programs.
BRANCH
BRANCH offset, (LabelO, Label 1,...)
When this command is executed, the program will jump to the program label based on the value
of offset. Offset is actually a program value and if offset is zero, the program jumps to the first
label, if offset is one, the program jumps to the second label, and so on.
Example:
BRANCH B2, (Lbll, Lbl2, Lbl3) ' If B2 = then goto Lbll
'IfB2 = 1 then goto Lbl2
'IfB2 = 2 then goto Lbl3
BUTTON
BUTTON Pin, Down, Delay, Rate, Var, Action, Label
This command is used to check the status of a switch. The command operates in a loop and con-
tinuously samples the pin, debouncing it and comparing the number of iteration performed with
the switch closed. The parameters are
Pin Pin number (0 to 7). PORTB pins only
Down State of pin when button is pressed (0 or 1)
Delay Delay before auto-repeat begins (0 to 255). If 0, no debounce or auto-repeat is
performed. If 255, only debounce, but no auto-repeat is performed
Rate Auto-repeat rate (0 to 255)
Var Byte variable used for delay /repeat countdown. Should be
initialised to before use
Action State of pin to perform goto (0 if not pressed, 1 if pressed)
Label Program execution continues at this label if Action is true
Figure 4.1 shows the two types of switches that can be used with this command.
For example, the following command checks for a switch pressed on pin 2 (of PORTB) and jumps
to Loop if it is not pressed (this command assumes that the port pin will be logic when the
switch is pressed, i.e. the figure on the left in Figure 4.1):
BUTTON 2, 0, 255, 0, B0, 0, Loop
88 PIC BASIC projects
+5V
4
■> To input pin
10K
Figure 4.1 Switches that can be used for the Button command
The following command checks for a switch pressed on pin 2 as above, but jumps to Loop if the
switch is pressed:
BUTTON 2, 0, 255, 0, BO, 1, Loop
CALL
CALL Label
This command executes the assembly language subroutine named Label. For example, the com-
mand calls to assembly language routine with the name calculate.
CALL calculate
FOR... NEXT
FOR index = Start TO End (STEP (-) Inc)
(body)
NEXT index
This command is used to perform iterations in a program. Index is a program variable which holds
the initial value of the iteration count Start. End is the final value of the iteration count. STEP is
the value by which the index is incremented at each iteration. If no STEP is specified, the index is
incremented by 1 . The iteration repeats until index = End and then execution continues with the
next instruction following the NEXT. Index can be a byte (0 to 255), or a word (0 to 65535).
In the following example, the two statements enclosed within the FOR... NEXT are executed 10
times.
FOR B0 = 1 TO 10
Bl =B1 + 1
B2 = B2 + 1
NEXT B0
PicBasic and PicBasic Pro programming 89
or in the following example, the index is incremented by 2 in each iteration.
FOR BO = 1 TO 100 STEP 2
Bl =B0 + 2
NEXT BO
GOSUB.. .RETURN
GOSUB Label
This program calls a subroutine starting at Label. It is like a GOTO command, but here the program
returns when the RETURN statement is reached, and continues with the instruction after the
GOSUB. The RETURN statement has no parameters. A subroutine has the following characteristics:
• A label to identify the starting point of the subroutine
• Body of the subroutine where the required operation is performed
• RETURN statement to exit the subroutine and return to the main calling program
Subroutines can be nested in PicBasic where a subroutine can call to other subroutines. The nest-
ing should be restricted to no more than four levels deep. In the following example, the subrou-
tine labelled INC increments variable B 1 by one and then returns to the main program. On return
to the main program, the statement B2 = Bl is executed.
BO =
Bl = 1
GOSUB INC ' Jump to subroutine INC
B2 = B 1 ' Subroutine returns here
INC: ' Start of the subroutine
Bl = Bl + 1 ' Body of the subroutine
RETURN ' End of the subroutine
GOTO
GOTO Label
This command causes the program execution to jump to the statement beginning at Label. For
example,
GOTO Loop
Loop:
IF... THEN
IF Comp (AND / OR Comp) THEN Label
90 PIC BASIC projects
This statement is used to perform comparisons (Comp) in a program. If the result of the compari-
son is true then the program jumps to the statement at Label, otherwise execution resumes with
the statement following IF. . .THEN.
A comparison can relate to a variable, to a constant, or to other variables. All comparisons are
unsigned and the following comparison operators can be used:
<
less than
<=
less than or equal
=
equal
<>
not equal
>=
greater than or equal
>
greater than
Additionally, logical operators AND and OR can be used in a comparison operation. For example,
IF BO > 10 THEN CALC ' Jump to CALC if BO > 10
CALC:
Another example is given below. In this example, if B2 is greater than 40 and at the same time B3
is less than 20 then the program jumps to the statement at label EXT. Otherwise, execution con-
tinues with the statement after the IF. . .THEN.
IF B2 > 40 AND B3 < 20 THEN EXT
EXT:
It is important to be careful that only a Label can be used after the THEN statement.
4.1.4 Other PicBasic commands
We shall now briefly look at the remaining PicBasic commands in alphabetical order which are
useful during the program development. More details about these commands can be obtained
from the PicBasic manual.
EEPROM
EEPROM Location, (constant, constant, , constant)
This command stores constants in consecutive bytes in on-chip EEPROM memory. The command
only works with the PIC microcontrollers that have EEPROM, such as the PIC16F84, PIC16F877,
PicBasic and PicBasic Pro programming 9 1
etc. Location is optional, and if omitted the first EEPROM location is assumed. Constants can be
numeric constants or string constants. Strings are stored as consecutive bytes of ASCII values. An
example is given below.
EEPROM 3, (5, 2, 8) ' Store 5 in location 3,
' 2 in location 4, and 8 in
' location 5
END
END
Stops execution and enters low power mode. The command has no parameters.
HIGH
HIGH Pin
Makes the specified pin an output pin and sets it to logic 1 . Pin only applies to PORTB pins and
it can take values from to 7. In the following example, bit 1 of PORTB is configured as an out-
put pin and is set to logic 1 :
HIGH1
I2CIN
I2CIN Control, Address, Var, (, Var)
This command is used to read data from serial EEPROMs with a 2-wire I 2 C interface. A list of some
compatible devices is given in Table 4.4. The lower 7 bits of the Control byte contain a 4-bit control
code, followed by the chip select or additional address information, depending on the device used.
As shown in Table 4.4, the 4-bit control code for EEPROMs is "1010". The high-order bit (MSB) of
the Control byte is a flag indicating whether the Address is to be sent as 8 bits or 16 bits. If the flag
is low, the Address is sent as 8 bits, and if it is high, the Address is sent as 16 bits. (, Var) shown in the
command list is used only for 1-bit information. The I 2 C data and clock lines are predefined in the
PicBasic library as bit of PORTA (RAO) and bit 1 of PORTA (RA1), respectively.
For example, when communicating with a 24LC02B EEPROM, the required Address is 8 bits, the
control code is "1010" and chip select or additional address information is not required and can
be assumed to be 0. The required Control byte is then "01010000".
Figure 4.2 shows how the 24LC02B (or any other serial EEPROM) can be connected to a PIC
microcontroller. In this example, a PIC16F84 is used and pin RAO and RA1 are connected to the
data and clock pins of the EEPROM, respectively. These are the only connections required to
communicate with an I 2 C-compatible device. As shown in the figure, the I 2 C lines should be con-
nected to Vdd (+5 supply) with 4.7K resistors.
92 PIC BASIC projects
Table 4.4 Some I 2 C compatible EEPROMs
Device
Capacity
Control
Address size
24LC01B
128 bytes
OlOlOxxx
8 bits
24LC02B
256 bytes
OlOlOxxx
8 bits
24LC04B
5 12 bytes
OlOlOxxb
8 bits
24LC08B
1 K bytes
OlOlOxbb
8 bits
24LC16B
2 Kbytes
OlOlObbb
8 bits
24LC32B
4 K bytes
HOlOddd
16 bits
24LC65B
8 K bytes
llOlOddd
16 bits
bbb = block select bits (each block is 256 bytes)
ddd = device select bits
xxx = don't care
A +5V
R1
4.7K
14
n
VDD
MCLR RA0
RA1
PIC
16F84
OSC1
Vss
OSC2
16 15
c 1z dnh^
22p?T 4MHz T~;
10K
111
18
8
10K
6
Vcc
SDA
SCL
24LC02B
AO
A1
A2 WP
Vss
7
Serial EEPROM
C2
22pF
Figure 4.2 I 2 C Connections to a PIC microcontroller
In the following example, a data byte is read from address 20 of the serial EEPROM and stored in
variable B 1. Note that the Control byte is set to "01010000", Address is assigned variable BO and
value 20 stored in it, and the byte read from the EEPROM is stored in data register B 1 .
Symbol con = %0 10 10000
Symbol addr = BO
addr = 20
I2CIN con, addr, Bl
' Set address to 20
' Read from address 20 to B 1
PicBasic and PicBasic Pro programming 93
I2COUT
12 C OUT Control, Address, Value (, Value)
This command is used to send data to an I 2 C compatible device such as a serial EEPROM
described in command I2CIN. The (, Value) in the command is used for 16-bit information.
When writing data to an EEPROM, it is necessary to wait about 10 ms (device dependent) for the
write operation to complete before attempting to write again. In the example given below, data byte
10 is written to address 30, and also data byte in variable B5 is written to address 31 of an EEPROM.
Symbol con = %01010000
Symbol addr = BO
addr = 30 ' Set address to 30
I2COUT con, addr, (10) ' Write byte 10 to address 30
PAUSE 10 'Wait 10ms
addr = 31 'Set address to 3 1
I2COUT con, addr, (B5) ' Write byte in B5 to address 3 1
PAUSE 10 'Wait 10 ms
INPUT
INPUT Pin
This makes the specified PORTB pin an input. Pin is from to 7. For example,
INPUT 2 ' Make RB2 an input pin
LOOKDOWN
LOOKDOWN Search, (Constant, Constant, ), Var
This command provides a look-up table. It looks down a list of Constants and compares each one
with the Search value. If a match is found, the position of the match is stored in Var. Note that the
first Constant is assumed to be at position 0. The Constant list can be numeric or string constants.
In the following example, if we assume that variable B0 has value 5 then variable B 1 will contain
3 which is the position of 5 in the table:
LOOKDOWN B0, (0, 8, 9, 5, 12, 0, 1), Bl
LOOKUP
LOOKUP Index, (Constant, Constant,....), Var
This command is used to retrieve values from a table. When Index is 0, Var is loaded with the first
Constant; when Index is 1, Var is loaded with the second Constant and so on. In the following
94 PIC BASIC projects
example, if we assume that variable BO has value 3, variable B 1 will be loaded with 8 which is the
3rd element in the table starting from 0:
LOW
LOOKUP BO, (0, 9, 0, 8, 12, 32), Bl
LOW Pin
This command makes the specified pin an output pin and clears it to logic 0. Pin only applies to
PORTB pins and it can take values from to 7. In the following example, bit 2 of PORTB is con-
figured as an output pin and is cleared to logic 0:
LOW 2
NAP
NAP Period
The NAP command places the PIC microcontroller in low-power mode for a while to save power
in battery applications. The Period is a variable from to 7 and the approximate delay is given in
Table 4.5.
Table 4.5 Delay in NAP command
Period
Delay (s, approx)
18 X 10~ 3
1
36 X 10~ 3
2
72 X 10~ 3
3
144 X 10" 3
4
288 X 10" 3
5
576 X 10~ 3
6
1.152
7
2.304
In the following example the microcontroller is put into low power mode for just over 1 s:
NAP 6
OUTPUT
OUTPUT Pin
This command makes the specified pin of PORTB an output pin. Pin can take values from to 7.
In the following example, bit 2 of PORTB (RB2) is made an output pin:
OUTPUT 2
PicBasic and PicBasic Pro programming 95
PAUSE
PAUSE Period
This is one of the commonly used commands to delay a program by a specified amount. Period is
in milliseconds and can range from 1 to 65,535 ms (i.e. just over one minute). PAUSE does not put
the microcontroller into low-power mode. In the following example, the program is delayed by 1 s:
PAUSE 1000
PEEK
PEEK Address, Var
This command is used to read the value of a RAM register at the specified Address and then put
the value into variable Var. The PEEK command can be used to access all registers of the PIC
microcontroller including the Port registers, A/D converter registers, etc.
In the following example, the 8-bit value of PORTB is read and stored in variable BO:
Symbol PORTB = 6 ' PORTB register address
PEEK PORTB, BO ' Read PORTB into BO
POKE
POKE Address, Var
This command is used to send data to a RAM register at the specified Address. The POKE com-
mand can be used to send data to all accessible registers of the PIC microcontroller, including the
PORT registers, PORT direction registers, A/D converter registers, etc.
In the following example, TRISB is cleared to so that all PORTB pins are outputs. The hexa-
decimal value 24 is sent to PORTB.
Symbol TRISB = $86 ' TRISB register address
Smbol PORTB = 6 ' PORTB register address
POKE TRISB, ' Clear TRISB
POKE PORTB, $24 ' Send $24 to PORTB
POT
POT Pin, Scale, Var
This command could be useful to read an analogue voltage if the microcontroller has no built-in
A/D converter. Pin is a PORTB pin and can take a value between and 7. For this command to
work, a resistor and a capacitor are serially connected to a port pin as shown in Figure 4.3. When
a voltage is applied to a resistor-capacitor circuit, the voltage across the capacitor rises exponen-
tially as the capacitor is charged through the resistor. The charge time is dependent on the value
of the resistor and the capacitor.
96 PIC BASIC projects
Port pin r>
1
5-50K
— L - 0.1 mF
Figure 4.3 Resistor and capacitor connected to an I/O pin
When the POT command is used, the capacitor is initially discharged by the I/O pin by placing the
pin in output mode. After that, the I/O port is changed to an input port and starts timing the voltage
across the capacitor until the voltage reaches the threshold value of the I/O pin. When this happens,
the calculated charge time is converted into a number between and 255 and is stored in Var. The
Scale value should be set experimentally. To do this, set the device to maximum resistance and set
the Scale to 255. The value returned in Var will be the proper scale value for the chosen compo-
nents. An example is given below where the resistor-capacitor are connected to pin 1 of PORTB,
the Scale value is set to 255 and the output value is stored in BO.
POT 1,255, BO
PULSIN
PULSIN Pin, State, Var
The PULSIN command measures the pulse width of any signal connected to a PORTB pin. With
a 4 MHz crystal or resonator, the pulse width will be measured in 10 jjls units. If State is 0, the
width of a low pulse is measured; if Scale is 1, the width if a high pulse is measured. The meas-
ured value in 10 (jls units is stored in variable Var. Var can be a byte or a word. If a word is used,
it can take values 1 to 65,535, i.e. the minimum pulse width that can be measured is 10 jjls and the
maximum is 655,350 (jls. If a byte is used, the range of the measurement is 10 to 2550 (jls.
PULSOUT
PULSOUT Pin, Period
This command generates a pulse on a PORTB pin {Pin can be to 7) of specified Period in 10 |jls
units. The Period is a word and thus pulses of up to 655,350 (xs can be generated. The specified
pin is automatically made an output pin.
For example, to generate a 500- (jls pulse on pin 1 of PORTB, we need the command
PULSOUT 1,50
PWM
PWM Pin, Duty, Cycle
PicBasic and PicBasic Pro programming 97
This command outputs a Pulse-Width-Modulated (PWM) signal on the specified PORTB pin
{Pin can be to 7). The Duty is the pulse duty-cycle and can range from to 255. corresponds to
a 0% duty-cycle, and 255 corresponds to a 100% duty-cycle. The generated PWM pulse is repeated
Cycle times. The specified port Pin is made an output just before the command is executed and
reverts to an input after the pulse is generated.
In the following example, a 200-cycle PWM signal is generated on bit of PORTB with a duty-
cycle of 50%:
PWM 0, 127, 200
Another use of this command is to generate an analogue signal by sending the output to a
resistor-capacitor circuit as shown in Figure 4.4. In this circuit, the voltage across the capacitor will
vary depending on the Duty and the Cycle of the pulses.
10K
Port pin|> 1 1 • > Analogue out
f
MF
Figure 4.4 Using PWM signal for D/A conversion
RANDOM
RANDOM War
This command generates a random number and stores in word variable Var. For example, to gen-
erate a random number and store in Wl use the command:
RANDOM Wl
READ
READ Address, Var
This command is used to read a byte from the specified Address of the built-in EEPROM mem-
ory. The byte read is stored in variable Var. This command can only be used with PIC microcon-
trollers that have built-in EEPROM memory (such as PIC16F84, or PIC16F877).
In the following example, the byte at address 10 of EEPROM is read and stored in variable B 1 :
READ 10, B 1 ' Read byte at address 10
' and store in B 1
REVERSE
REVERSE Pin
This command reverses the mode of a PORTB pin (Pin can be from to 7). If the pin is an input,
it is made an output. Similarly, if the pin is an output, it is made an input.
98 PIC BASIC projects
In the following example, bit 2 of PORTB is first made an output pin, then changed to an input pin:
OUTPUT 2
REVERSE 2
' RB2 is output pin
' RB" is an input pin
SERIN
SERIN Pin, Mode, (Qual, Qual,, ), Item, Item,
This command is used to receive RS232 serial asynchronous data on a PORTB pin (pin is
between and 7) using 8-bit data, no parity bit, and one stop bit. As shown in Table 4.6, Mode
defines the baud rate and whether or not the pin data is inverted. For example, if Mode is N9600,
the data is inverted and the selected baud rate is 9600.
Table 4.6 Selecting the baud rate with Mode
Symbol
Value
Baud rate
Mode
T2400
2400
True
T1200
1
1200
True
T9600
2
9600
True
T300
3
300
True
N2400
4
2400
Inverted
N1200
5
1200
Inverted
N9600
6
9600
Inverted
N300
7
300
Inverted
The RS232 signal levels are ± 12 V and level converter circuits (such as MAX232) are normally
used to convert the RS232 signal levels to TTL and the TTL levels back to RS232 levels. The I/O
specifications of PIC microcontrollers allow RS232 signals to be directly connected to a port pin.
As shown in Figure 4.5, a resistor is all that is needed to receive RS232-compatible signals on a
pin. When used in this mode, the data is to be inverted (i.e. use the "N" versions of the mode sig-
nals in Table 5.6)
Port pin
22K
X
RS232 TX (Pin 3 on DB9 connector)
RS232 Ground (Pin 5 on DB9 connector)
Figure 4.5 Connecting a RS232 signal to a port pin
A number of qualifiers, enclosed in brackets, can be used with the SERIN command such that these
bytes must be received before receiving the data items. Once the qualifiers are satisfied, SERIN
receives the serial data and stores in Items,. The Item variable may be preceded by the hash character
("#"). This will convert the decimal number received into ASCII equivalent and store it in Item.
PicBasic and PicBasic Pro programming 99
In the following example, pin 1 of PORTB (RB 1) is defined as the serial I/O pin and the port pin
is connected to the RS232 serial line using a resistor. The baud rate is assumed to be 4800. The
microcontroller waits until the character "X" is received from the line and then stores the next
byte in variable BO:
SERIN 1, N4800, ("X"), BO
SEROUT
SEROUT Pin, Mode, (Item, Item,...)
This command is similar to the SERIN command but is used to send RS232 asynchronous serial
data to a pin of PORTB {Pin can be between and 7). As before, Mode is used to set the commu-
nications baud rate. In addition to the standard inverted and non-inverted modes, it is also possi-
ble to set Open-Drain and Open-Collector modes where a pull-up resistor will be required at the
output of the pin. Table 4.7 gives a list of the available Modes.
Table 4.7 Selecting the baud rate with Mode
Symbol
Value
Baud rate
Mode
T2400
2400
True
T1200
1
1200
True
T9600
2
9600
True
T300
3
300
True
N2400
4
2400
Inverted
N1200
5
1200
Inverted
N9600
6
9600
Inverted
N300
7
300
Inverted
OT2400
8
2400
Open Drain
OT1200
9
1200
Open Drain
OT9600
10
9600
Open Drain
OT300
11
300
Open Drain
ON2400
12
2400
Open Source
ON 1200
13
1200
Open Source
ON9600
14
9600
Open Source
ON300
15
300
Open Source
Data byte Item is sent to the specified port pin in serial format. The Item can be a string constant or a
numeric value. A string constant consists of characters and each character of the string is sent out. For
example, the string "COMPUTER" is sent out as 8 individual characters. A numeric value will send
the corresponding ASCII character. For example, 13 is the carriage-return character, 65 is character
"A" and so on. A numeric value can be preceded by the hash character "#" and this will send out the
ASCII representation of its decimal value. For example, #345 will be sent as "3", "4", and "5".
1 00 PIC BASIC projects
In the following example, it is assumed that pin 1 of PORTB (RBI) is used as the serial I/O pin
and it is configured for 4800 baud. ASCII value of variable BO is sent out from this pin, followed
by a carriage-return.
SEROUT 1, N4800, (#B0, 13)
SLEEP
SLEEP Period
The SLEEP command is used to put the microcontroller in low-power mode and stops the micro-
controller running for the specified Period. The Period is a word and can range from 1 to 65,535
and represents increments of 2.3 s. For example, a value of 1 will make the microcontroller sleep
for 2.3 s, a value of 2 will make the microcontroller sleep for 4.6 s and so on. The maximum value
of 65,535 makes the microcontroller sleep just over 18 h.
In the following example, the microcontroller sleeps for 23 s:
SLEEP 10
SOUND
SOUND Pin, (Note, Duration, Note, Duration, )
This command is used to generate sound on a specified PORTB pin of the microcontroller (Pins
are between and 7). Note can take values from to 255 and these values do not correspond to
the musical notes. A represents silence. Values from 1 to 127 are tones (1 is lower frequency
than 127), and values from 128 to 255 are white noise (128 is lower frequency than 255). The
sound continues for a length of time specified by Duration. Duration is measured in milliseconds
and it can take values between and 255. The SOUND command produces TTL level square
waves and it is possible to connect a speaker to the output pin as shown in Figure 4.6.
22 uF
Port pin O \\ \-
Speaker
Figure 4.6 Connecting a speaker for the SOUND command
In the following example, a sound with note 20 and duration 100 ms is sent to pin of PORTB.
Then, another sound with note 23 and duration 200 ms is sent out from the same port pin.
SOUND 0, (20, 100, 23, 200)
TOGGLE
TOGGLE Pin
This command makes the specified Pin an output pin and inverts the state of this pin (Pin can take
values from to 7).
PicBasic and PicBasic Pro programming 101
In the following example, bit of PORTB (RBO) is first made low, and then changed to high using
the TOGGLE command:
LOW0
TOGGLE
WRITE
WRITE Address, Value
The WRITE command writes the Value byte to the specified EEPROM address. This command is
only valid for the PIC microcontrollers which have built-in EEPROM memories.
In the following example byte in variable BO is written to EEPROM address 2:
WRITE 2, BO
4.1.5 Recommended PicBasic program structure
There are many different ways in which a PicBasic program can be written. It is important to note
that a program should be written in such a way that it is easily maintainable by other people. This
is specially important if you work in a firm and others may have to upgrade or maintain your pro-
gram. The following steps should be followed to develop a maintainable program:
• Use a header in your programs. This header should briefly describe the function of the pro-
gram. In addition, the author of the program, the program creation date, program file name,
and any program modifications should be described in the header.
• Use comments in your programs to describe what you are trying to do. The comments can be
used at the beginning of a piece of code, or after every statement.
• Use symbols as much as possible in your programs. Symbols make your programs more readable.
The author recommends that you use a template similar to the one given in Figure 4.7 when develop-
ing PicBasic programs. As you can see in this figure, the header includes a brief description of the
program, name of the author, the date, and the filename of the program. Comments are used in
every line of the program to clarify the actions of the program.
4.2 PicBasic Pro language
PicBasic Pro is a full-featured compiler and is for serious or professional PIC programmers.
PicBasic Pro has many additional commands compared to the standard PicBasic compiler. In
addition, the variables, constants and symbols are treated differently in PicBasic Pro. In this sec-
tion, we shall only be looking at the commands which are specific to PicBasic Pro language, and
which have not been described in Section 4. 1 . Also, various features of the PicBasic Pro language
are described in this section.
1 02 PIC BASIC projects
LED FLASHING PROGRAM
This program flashes and LED connected to port RBO of PORTB. The
Led is flashed with 1 second intervals.
Author:
Dogan Ibrahim
Date:
September, 2005
File:
LED.PBC
Modifications
SYMBOLS
Symbol LED =
Symbol TRISB = $86
Symbol PORTB = $06
' START OF MAIN PROGRAM
POKE TRISB,
' Define RBO as LED
' TRISB address
' PORTB address
AGAIN:
HIGH LED
PAUSE 1000
LOW LED
PAUSE 1000
GOTO AGAIN
END
' Set PORTB pins as outputs
' Turn ON LED
' Wait 1 second
' Turn OFF LED
' Wait 1 second
' Repeat
' End of program
Figure 4.7 Recommended PicBasic program template
4.2. 1 PicBasic Pro variables
Variables in PicBasic Pro are stored in the general purpose RAM registers and are declared using
the VAR keyword. Each variable has a name and a variable type. A variable type can be a bit, a
byte, or a word. Some example variable declarations are
Total
VAR
word
Count
VAR
byte
Flag
VAR
bit
PicBasic and PicBasic Pro programming 103
The VAR keyword can also be used to create an alias for a variable (i.e. another name). In the fol-
lowing example, Sum is another name for Total:
Sum VAR Total
The individual bits of a variable can be accessed by writing the variable name, followed by a dot
"." character, and then the bit number (0 to 15), or the keyword BIT followed by the bit number
(e.g. BITO to BIT 15). The following are examples of accessing bit of variable Total:
Total.O
Total.BITO
Arrays of variables can be created in PicBasic Pro by writing the name of the array, followed by
the keyword VAR, and then the type and the size of the array. For example, a byte array called Sum
with 10 elements of type byte can be declared as
Sum VAR byte[10]
In the above example, the first element of the array is Sum[0], and the last element is Sum[9].
Arrays have a size-limit in PicBasic Pro.
• Maximum size of a bit array is 256
• Maximum size of a byte array is 96 (microcontroller-dependent)
• Maximum size of a word array is 48 (microcontroller-dependent)
4.2.2 Constants
Constants in the PicBasic Pro language are declared using the CON keyword. A constant value
cannot be changed in a program.
In the following example, Maxim is declared as 10 and its value cannot be changed in the program:
Maxim CON 10
4.2.3 Comments
Comments in PicBasic Pro are declared same as in the PicBasic language, i.e. using the REM
keyword or a single quote at the beginning of a line.
4.2.4 Multi-statement lines
Multi-statement lines are created as in PicBasic, i.e. by separating each statement with a colon ":"
character.
1 04 PIC BASIC projects
4.2.5 INCLUDE
Other PicBasic Pro source files can be included in a program as in PicBasic language.
4.2.6 DEFINE
This command defines various compiler options, such as the clock oscillator frequency, pin num-
ber, etc.
4.2. 7 Line extension
When writing long programs, it may be necessary to continue part of a statement on a new line.
A line can be extended by typing the line extension character "_" as the last character in the line
to be continued. For example,
Iteml, Item2, Item3, Item4, _
Item 5, Item6
4.2.8 Accessing ports and other registers in PicBasic Pro
PIC microcontroller ports or any other registers can easily be accessed by simply writing the
name of the port or the register and using equate "=" character. For example,
A = PORTA
UP = PORTB & $F0
PORTB = $2F
INTCON = $0F
The bits of a port or a register can be accessed by simply writing the name of the port or the regis-
ter, followed by a dot "." character and the PORTBit to be accessed. For example,
L = PORTB. 1 ' Read bit 1 of PORTB and load into L
L = PORTB.BIT1 ' Read bit 1 of PORTB and load into L
K = STATUS. ' Read bit of STATUS register and load into K
In most of the PicBasic I/O commands, Pin is used to define a pin of PORTB where Pin can take
a value from to 7 corresponding to PORTB pins. In a similar manner, PicBasic allows the use
of numbers to 15 to access port I/O pins. When only a number is used to access a port pin, the
port and the pin number accessed depends on the package size of the microcontroller used. Table 4.8
shows the Pin definitions for 8 to 40 pin PIC microcontrollers.
For example, assuming we are using an 18-pin PIC microcontroller, the PicBasic command
SOUND 3, 10,100
PicBasic and PicBasic Pro programming 105
generates a sound with note 10 and duration 100 ms from bit 3 of PORTB (i.e. RB3). In PicBasic
Pro, we can use the same statement, or we can write
SOUND PORTB.3, 10, 100
If we wish to generate the sound from bit of PORTA, in PicBasic Pro we can write
SOUND PORTA.0, 10, 100
or
SOUND 8, 10, 100
There is no way of generating a sound from PORTA using the PicBasic language.
Table 4.8 Port I/O Pin definitions
PIC micro Size
Pin 0-7
Pin 8-15
8 pin
GPIO
-
18 pin
PORTB
PORTA
24 pin (except 14,000)
PORTB
PORTC
28 pin
PORTC
PORTD
40 pin
PORTB
PORTC
The direction of a port is determined by loading the corresponding TRIS register. For an output
pin, a is loaded into the corresponding TRIS register, and for an input pin a 1 is loaded into the
corresponding TRIS register. In PicBasic Pro, the TRIS register can be accessed directly like any
other register. For example, to configure all PORTB pins as outputs and then send the hexadeci-
mal value $FF to PORTB we can write
TRISB =
PORTB = $FF
4.2.9 Arithmetic operators
PicBasic Pro supports more arithmetic operators than PicBasic. Table 4.9 lists all the arithmetic
operators supported by PicBasic Pro. In this section, we shall be looking only at these additional
operators.
Shift
The shift operators "<<" and ">>" are used to shift a value left or right, respectively, to 15
times. Zeroes are placed to the shifted positions. Shifting left is same as multiplying the number
by 2, and shifting right is same as dividing the number by 2.
1 06 PIC BASIC projects
Table 4.9 PicBasic Pro arithmetic operators
Arithmetic Operator
Description
+ - * /
Add, subtract, multiply, divide
**
Top 1 6 bits of multiplication
*/
Middle 16 bits of multiplication
//
Remainder
« »
Shift left, shift right
ABS
Absolute value
COS
Cosine
DCD
Decode
DIG
Digit
MAX MIN
Maximum, minimum
NCD
Encode
REV
Reverse bits
SIN
Sine
SQR
Square root
& 1 A ~
Bitwise AND, OR, EXOR, NOT
&/ 1/ A /
Bitwise NAND, NOR, INOR
In the following first example, variable Cnt is shifted left twice. In the second example, variable
Sum is shifted right 3 times.
Cnt = cnt << 2 ' Shift left Cnt by 2 places
Sum = Sum >> 3 ' Shift right Sum by 3 places
ABS
Operator ABS returns the absolute value of a number. In the following example, the absolute
value of variable p is returned:
ABSp
' Return the absolute value
COS
Returns the cosine of a number. The result is in 2's complement format in the range —127
to +127. The number must be in radians in the range to 255. In the following example, the
cosine of 8 radians is returned:
Angle = COS 8
' Return the cosine of 8
PicBasic and PicBasic Pro programming 107
DCD
This operator is used to set a bit of a byte or a word to 1 . All other bits are set to 0. For example,
to set bit 4 of a byte we can write
B4 = DCD 4 ' Set bit 4 of variable B4
Where variable B4 will take the binary value %000 10000
DIG
This operator returns a digit of a number. The number can be up to 4 digits with the rightmost
digit being digit 0. For example, if variable Sum is equal to 678, the first digit (number 7) can be
extracted as
Sum = 678 ' Sum = 678
P = Sum DIG 1 ' P = 7
NCD
The NCD operator is used to find the highest bit number set in a number. The bit numbers can
range from 1 to 16. A zero is returned if no bit is set. In the following example, variable P = 6
since the highest bit set in the number is the sixth bit (starting from 1).
P = NCD %0010101 1 ' Highest bit set is 6
SIN
This operator is similar to the COS operator and it returns the sine of a number. The number must
be expressed in radians and it must be between and 255. For example, to find the sine of 10 radi-
ans, use
P = SIN 10
SQR
This operator returns the square root of a number. The result is an integer number. For example,
to find the square root of variable Total, use
N = SQR Total ' Find square root of Total
4.2. 10 PicBasic Pro commands
PicBasic Pro has over 80 commands. Some commands are similar to the PicBasic commands with
minor changes. For example, the range of the Pin variable is from to 15, instead of to 7. It is the
author's recommendation that you use the port name, followed by a dot and the bit number when you
wish to access a port pin. This makes your programs much more readable and easier to maintain.
In this section, we shall only look at the commonly used commands which are specific to the
PicBasic Pro language. Further information about these or any other commands can be obtained
from the PicBasic Pro user manual.
1 08 PIC BASIC projects
ADCIN
ADCIN Channel, Var
This command is used to read the on-chip A/D converter. This is not a very useful command and
we shall see in the projects section how to read data from the A/D channel of a PIC microcontroller.
BRANCHL
BRANCHL Index, (Label, Label, )
The BRANCH command used in the PicBasic language causes a limited range of branch (usually
1 K). The BRANCHL command can be used to create longer jumps in the program memory. The
BRANCHL command is slower than the BRANCH command and generates more assembly code.
CLEAR
CLEAR
This command clears (zeroes) all the RAM registers in each bank.
CLEARWDT
CLEARWDT
If the watchdog timer is enabled, it can time out and reset the program to the beginning (address 0).
The CLEARWDT command is used to reset the watchdog timer so that it does not time out.
COUNT
COUNT Pin, Period, Var
This command is used to count the number of pulses that occur on Pin during the Period and
stores the result in Var. Pin can take values to 15 but the "Portname. number" format is recom-
mended (e.g. PORTB.0).
The highest frequency that can be counted with a 4 MHz crystal clock is 25 kHz, and 125 kHz
when a 20 MHz clock is used. In the following example, the number of pulses on bit of PORTB
are counted in 100 ms and stored in variable Cnt:
COUNT PORTB.0, 100, Cnt
DATA
DATA @ Location, Constant, Constant,....
This command stores constants in the on-chip EEPROM memory during the programming of the
device (not when the program is run). The command can only be used with the PIC microcon-
trollers that have on-chip EEPROMs. Location denotes the starting address of the EEPROM and
if omitted, address is assumed.
The following example shows how the numbers 5, 10, 15, and 20 can be stored in EEPROM starting
from address 6:
DATA @6, 5, 10, 15, 20
PicBasic and PicBasic Pro programming 109
DTMFOUT
DTMFOUT Pm, Onms, Offms, [Tone, Tone, ]
This command produces Touch Tones normally available in keyboards and mobile phones. Pin can
take a value between and 15 (or Portname. number) and the specified pin is made an output. Onms
is the duration of each tone in milliseconds, and Offms is the number of milliseconds pause between
each tone. If the Onms or the Offms are not specified, they default to 200 ms and 50 ms, respectively.
A Tone can take a value between and 15. Tones to 9 are the same as on a telephone keypad.
Tone 10 is the * key, Tone 1 1 is the # key, and Tones 12-15 are the extended keys A to D. The
sound generated by the DTMFOUT should be smoothed using resistor-capacitor filters. It is rec-
ommended to use a high clock rate (e.g. 20 MHz) to get a smooth signal after the filtering.
In the following example, the DTMF tones for numbers 886 are sent from bit of PORTB with
the default duration and pause:
DTMFOUT PORTB.0, [8, 8, 6]
FREQOUT
FREQOUT Pin, Onms, Frequency 1, [, Frequency 2]
This command generates a signal with one or two different frequencies on the specified Pin for Onms
milliseconds. Pin is automatically made an output and it can be to 15 or a Portname. number. The
generated signal is a square wave and filtering may be required to obtain a smooth signal.
In the following example, a 1 kHz signal is generated on port of PORTB for 3 s:
FREQOUT PORTB.0, 3000, 1000
HPWM
HPWM Channel, Dutycycle, Frequency
Some PIC microcontrollers have one or more built-in circuits to generate pulse width-modulated
square- wave signals (PWM). For example, PIC16F877 has two PWM Channels. Channel 1 is
known as CCP1 (also PORTC.2) and Channel 2 is known as CCP2 (also PORTC.l).
Dutycycle can vary from to 255 which corresponds to 0% (low all the time) to 100% (high all
the time), respectively. A value of 127 gives 50% duty cycle. The highest Frequency is 32,767 Hz,
and on microcontrollers with two channels, the Frequency must be the same on both channels.
The PWM signal is output from the specified pin continuously in the background while the pro-
gram executes other instructions.
In the following example, a 1 kHz, 50% duty cycle PWM signal is generated from Channel 1
(CCP1) of a PIC16F877 type microcontroller:
HPWM 1, 127, 1000
110 PIC BASIC projects
HSERIN
HSERIN2
These commands are only available on microcontrollers that have built-in serial port devices such
as an US ART. The use of these commands is complicated and more details can be obtained from
the PicBasic Pro user manual.
HSEROUT
HSEROUT2
These commands are only used on microcontrollers that have built-in serial port devices such as
an USART The commands are used to send out serial asynchronous data from the microcon-
troller with the required format. The use of these commands is complicated and more details can
be obtained from the PicBasic Pro user manual.
IF..THEN..ELSE
These commands are similar to the PicBasic IF.. THEN command but the PicBasic Pro language
provides more flexibility when one or more comparisons are made. These commands can be used
in the following formats:
Format 1:
IF Comparison [AND/OR Comparison...] THEN Label
Format 2:
IF Comparison [AND/OR Comparison. . .] THEN Statement
Format 3:
IF Comparison [AND/OR Comparison. . .] THEN
Statement....
ELSE
Statement
ENDIF
Some examples for the use of this command are given below:
Conditional statement:
IF PORTB.O = THEN Led = 1
Conditional jump:
IF (PORTB.O = 0) AND (PORTB.l = 1) THEN Loop
Multiple statements:
IF Cnt < 10 THEN A = A+1:B=B + 1
Multiple statements:
IF SUM < 10 THEN
Cnt = Cnt + 1
Tot = Tot + 1
ENDIF
PicBasic and PicBasic Pro programming 111
IF..THEN..ELSE
IF Total = 100 THEN
Flag = 1
ELSE
Flag =
ENDIF
PAUSEUS
PAUSEUS Period
This command pauses the program for Period microseconds. Period is a word in the range 1 to 65,535.
Thus, the maximum delay is 65.535 ms. PAUSEUS command assumes that we are using a 4 MHz
clock. The minimum delay that can be generated with PAUSEUS using a 4 MHz clock is 24 |xs.
REPEAT..UNTIL
REPEAT
Statement. . .
UNTIL Condition
This command is used to create loops in programs. The statements between the REPEAT and
UNTIL are executed until the specified Condition is true.
In the following example, the statements between REPEAT and UNTIL are executed 10 times:
k =
REPEAT
Sum = Sum + 1
Cnt = Sum
k = k+ 1
UNTIL k< 10
SELECT..CASE
SELECT CASE Var
CASE Exprl [,Expr...]
Statement...
CASE Expr2 [,Expr...]
Statement...
[CASE ELSE
Statement...]
END SELECT
This command is used instead of using multiple IF. THEN commands. The variable Var is com-
pared with different values (or ranges of values) and an action is taken based on its value. If Var
does not match any of the conditions, then the statements after the CASE ELSE are executed. The
IS keyword is used after CASE to specify a comparison other than equal to.
112 PIC BASIC projects
In the following example, if x is 1, B is set to 100. If x is 2, B is set to 6. If x is 3 or 4, B is set to
50. If x is greater than 120, B is set to 1. If x is none of these, then B is set to 0.
SELECT CASE x
CASE1
B = 100
CASE 2
B = 6
CASE 3, 4
B = 50
CASE IS > 120
B = 1
CASE ELSE
B =0
END SELECT
SHIFTIN
SHIFTIN Datapin, Clockpin, Mode, [Var{\bitsJ, Varfsbits },...]
The SHIFTIN command is used to read data one bit at a time as clock is sent out to the sending
device. The received data is stored in variables Var. Datapin is either from to 15 or a Portname.
number and specifies the pin number which is to receive the data, \bits optionally specify the
number of bits to shift in and if omitted, 8 bits are assumed. Clockpin is either to 15 or a. portname.
number and specifies the pin number where the clock is sent out. Mode has a value between and
7 and it specifies the mode of the clock operation as shown in Table 4. 10. For Modes between and 3,
the clock output is normally low and goes high to clock in a bit, then returns low. For Modes between
4 and 7, the clock output is normally high and goes low to clock in a bit, then returns high.
Table 4.10 SHIFTIN command clock Modes
Mode No.
Operation
Shift in MSB first. Read before sending clock. Clock normally low
1
Shift in LSB first. Read before sending clock. Clock normally low
2
Shift in MSB first. Read after sending clock. Clock normally low
3
Shift in LSB first. Read after sending clock. Clock normally low
4
Shift in MSB first. Read before sending clock. Clock normally high
5
Shift in LSB first. Read before sending clock. Clock normally high
6
Shift in MSB first. Read after sending clock. Clock normally high
7
Shift in LSB first. Read after sending clock. Clock normally high
In the following example, data bits are received into bit of PORTB and stored, LSB first, followed
by 8 data bits in variable B 1 . Mode is used here and the clock is sent out from bit 1 of PORTB.
SHIFTIN PORTB.0, PORTB. 1, 0, [Bl\8]
PicBasic and PicBasic Pro programming 113
SHIFTOUT
SHIFTOUT Datapin, Clockpin, Mode, [Var{\bitsJ, Var{\bits ),...]
This command is similar to SHIFTIN, but here, data bits are sent out one bit at a time. Datapin
can be to 15 or a Portname. number, \bits optionally specify the number of bits to be shifted out
and if omitted, 8 bits are assumed. Mode specifies which bit will be sent out first. If Mode is 0,
the LSB is sent out first followed by other data bits. If Mode is 1, the MSB is sent out first fol-
lowed by other data bits.
In the following example, the contents of variable B 1 are sent out as 8 bits, LSB first, from bit
of PORTB. Bit 1 of PORTB is used as the clock pin.
SHIFTOUT PORTB.0, PORTB. 1, 0, Bl
SWAP
SWAP Van Var
This command is used to swap the contents of two variables. It can be used with bit, byte, and
word variables.
In the following examples, values of variables Bl and B2 are exchanged:
SWAPB1,B2
WHILE..WEND
WHILE condition
Statement. . .
WEND
This is another command used to create loops in programs. The statements between the WHILE
and WEND are repeated while the Condition is true.
In the following example, the statements between WHILE and WEND are repeated 10 times:
k =
WHILE k < 10
Sum = Sum + 1
BO = BO + 2
k = k+ 1
WEND
4.3 Liquid crystal display (LCD) interface and commands
In many microcontroller-based applications, it is required to display a message or the value of a
variable. For example, in a temperature-control application, it may be required to display the value
114 PIC BASIC projects
of the temperature dynamically. Basically, three types of displays can be used in practise. These
are video displays, 7-segment LED displays, and LCD displays. Standard video displays require
complex interfaces and their cost is relatively high and their operation is not covered in this book.
7-segment LED displays are made up of LEDs. Although the 7-segment LEDs are bright, their dis-
advantage is the high power consumption which makes them unsuitable in many battery-operated
portable applications. We will see the operation of these devices in Chapter 5.
LCDs are alphanumeric displays which are frequently used in microcontroller-based applications.
Some of the advantages of LCDs are their low cost and low power consumption. LCDs are ideal
in low-power, battery-operated portable applications. These displays come in different shapes and
sizes. Some LCDs have 40 or more characters with several rows. Some more advanced LCDs can
be programmed to display graphics images. Some modules, such as the ones used in games, offer
colour displays while some others may incorporate back lighting so that they can be viewed in
dimly lit conditions. In this section, we shall be looking at how we can interface the standard
LCDs to a PIC microcontroller and what commands are available to use the LCDs.
There are basically two types of LCDs as far as the interface technique is concerned: parallel
LCDs and serial LCDs. Parallel LCDs are connected to the microcontroller I/O ports using 4 or 8
data wires and data is transferred from the microcontroller to the LCD in parallel form. Serial
LCDs are connected to the microcontroller using only one data line and data is transferred to the
LCD using the standard RS232 asynchronous data communication protocols. Serial LCDs are
easier to use but they usually cost more than the parallel ones. Serial LCDs also have the advan-
tage that only one wire is required to interface them to a microcontroller, thus saving the I/O pins.
In this section, we shall be looking at the interface and programming of both types of LCDs.
4.3. 1 Parallel LCDs
Figure 4.8 shows a typical parallel LCD. The programming of a parallel LCD is usually a complex
task and requires a good understanding of the internal operation of the LCDs, including the timing
requirements. Fortunately, the PicBasic Pro language provides special commands for displaying
data on HD44780 or compatible LCDs. All the user has to do is connect the LCD to the appropri-
ate I/O ports and then use these special commands to simply send data to the LCD. The standard
Figure 4.8 A typical parallel LCD
PicBasic and PicBasic Pro programming 115
PicBasic language does not provide any special commands for programming the parallel LCDs
and the programming of LCDs using the PicBasic language is described in the projects section
(Chapter 5) of this book.
HD44780 LCD module
HD44780 is one of the most popular LCD modules used in the industry and also by hobbyists. This
module is monochrome and comes in different shapes and sizes. Modules with line lengths of 8, 16,
20, 24, 32, and 40 characters can be selected. Depending on the model chosen, 1, 2, or 4 display
rows can be selected. The display has a 14-pin connector for interfacing to a microcontroller. Table
4. 1 1 shows the pin configuration of the LCD. A description of the pin functions is given below.
• V ss is the V or ground. V DD pin should be connected to the positive supply. Although the manu-
facturers specify a 5 V supply, the module can be operated with as low as 3 V or as high as 6 V
• Pin 3 is named as V EE and this is the contrast control pin. This pin is used to adjust the contrast of
the LCD and it should be connected to a variable voltage supply. A potentiometer is usually con-
nected between the power supply lines with its wiper arm connected to this pin so that the con-
trast can be adjusted. This pin can be connected to ground if contrast adjustment is not needed.
• Pin 4 is the Register Select (RS) and when this pin is LOW, data transferred to the display is treated
as commands. When RS is HIGH, character data can be transferred to and from the module.
• Pin 5 is the read/write (R/W) pin. This pin is pulled LOW in order to write commands or character
data to the LCD module. When this pin is HIGH, character data or status information cannot be
read from the module. This pin is usually connected to ground, i.e. the LCD is put into write mode.
• Pin 6 is the Enable (E) pin which is used to initiate the transfer of commands or data between the
LCD module and the microcontroller. When writing to the display, data is transferred only on the
Table 4.11 Pin configuration of HD44780 LCD
Pin No
Name
Function
1
Vss
Ground
2
V DD
Positive supply
3
Vee
Contrast
4
RS
Register select
5
R/W
Read/write
6
E
Enable
7
DO
Data bit
8
Dl
Data bit 1
9
D2
Data bit 2
10
D3
Data bit 3
11
D4
Data bit 4
12
D5
Data bit 5
13
D6
Data bit 6
14
D7
Data bit 7
116 PIC BASIC projects
HIGH to LOW transition of this pin. When reading from the display, data becomes available after
the LOW to HIGH transition of the enable pin and this data remains valid as long as the enable
pin is HIGH.
• Pins 7 to 14 are the eight data bus lines (DO to D7). Data can be transferred between the micro-
controller and the LCD module using either an 8-bit interface, or a 4-bit interface. In the latter case,
only the upper four data lines (D4 to D7) are used and the data is transferred as two 4-bit nibbles.
This mode has the advantage that fewer I/O lines are required to communicate with the LCD.
Connecting the LCD to the microcontroller
PicBasic Pro compiler by default assumes that the LCD is connected to specific pins of the micro-
controller unless told otherwise. It assumes the following connections:
LCD
Microcontroller
D4
RAO
D5
RA1
D6
RA2
D7
RA3
E
RB3
RS
RA4
Figure 4.9 shows the circuit diagram with the default connections between the LCD and the
microcontroller. In addition to the above connections, the R/W pin of the LCD is not used and is
connected to the ground. The contrast adjustment is done by connecting a potentiometer to V EE .
Notice that port pin RA4 is connected to +5 V supply with a resistor. This is because this pin is
open-drain output and should be pulled HIGH with a resistor.
VDD VEE
RS
E
D4
HD D5
44780 Rft
LCD D6
D7
11
12
13
14
nt
20K
T^l 1
4.7K
10K
+5V
VDD
MCLR
RA4
RB3
RAO
RA1
RA2
RA3
OSC1
PIC
Vss
OSC2
i?T 4MHz ~T:
C2
22pF
Figure 4.9 Default LCD connections to a PIC microcontroller
PicBasic and PicBasic Pro programming 111
When the above connections are made between the microcontroller and the LCD, we can simply
use the LCDOUT command to send data to the LCD module. Note that the connections between
the microcontroller and the LCD can be changed using a set of DEFINE commands to assign the
LCD pins to the PIC microcontroller.
In the following example, PORTB pins to 4 are used for LCD data (i.e. RBO connected to D4,
RB5 connected to D5, etc.), bit 4 of PORTB is connected to the RS pin of the LCD, bit 5 of PORTB
is connected to the E pin of the LCD, the LCD is set for 4-bits of operation, and the LCD is
assumed to have two rows.
DEFINE LCD_DREG
PORTB
' Set LCD data port to PORTB
DEFINE LCD_DBIT
' Set data starting bit to
DEFINE LCD_RSREG
PORTB
' Set RS register port to PORTB
DEFINE LCD_RSBIT
4
' Set RS register bit to 4
DEFINE LCD_EREG
PORTB
' Set E register port
DEFINE LCD_EBIT
5
' Set E register bit to 5
DEFINE LCD_BITS
4
' Set 4 bit operation
DEFINE LCD LINES
2
' Set number of LCD rows
The format of the LCDOUT command is
LCDOUT fern, fern,
where Item can be a command or data. A command is used to clear the display, home the cursor,
move the cursor to left or right, etc. It is important that a program should wait for at least half a
second before sending the first command to the LCD. This is because it can take quite a while
before the LCD initializes itself.
Table 4.12 gives a list of the available commands. All commands must be preceded by the hexa-
decimal number $FE. For example, to clear the display we have to issue the command
LCDOUT $FE, 1
Similarly, to move the cursor left by one position we have to issue the command
LCDOUT $FE, $10
Also, to move the cursor to the 5th position in the first row, we have to use the command
LCDOUT $FE, $80 + 5
Data is sent to the LCD using the LCDOUT command. The character set of the LCD is given in
Table 4. 13. A string can be sent to the LD by enclosing it in double-quotes. For example, the fol-
lowing command displays the string HELLO at the current cursor position:
LCDOUT "HELLO"
118 PIC BASIC projects
Table 4.12 LCD commands
Command
Operation
$FE, 1
Clear display
$FE, 2
Home cursor
$FE, $0C
Cursor off
$FE, $0E
Underline cursor on
$FE, $0F
Blinking cursor on
$FE, $10
Move cursor left by one position
$FE, $14
Move cursor right by one position
$FE, $80
Move cursor to the beginning of first row
$FE, $C0
Move cursor to the beginning of second row
$FE, $94
Move cursor to the beginning of third row
$FE, $D4
Move cursor to the beginning of fourth row
If a hash sign (#) precedes a variable (or if the characters DEC precede a variable), the ASCII repre-
sentation for each digit is sent to the LCD. For example, if the variable B 1 = 208, then the command
LCDOUT#Bl
or
LCDOUTDECB1
displays the characters "2", "0", and "8" on the LCD.
If character BIN precedes a variable, the ASCII representation of its binary value is sent to the
LCD. For example, if the variable B 1 = 9, then the command
LCDOUTBINB1
displays the characters "1001" on the LCD.
A numeric value preceded by HEX will send the ASCII representation of its hexadecimal value
to the LCD. For example, if B0 = 255, then the command
LCDOUT HEX B0
will display "FF" on the LCD.
It is also possible to send repeated characters to the LCD. In the following example, the charac-
ters "AAAAA" are sent to the LCD:
LCDOUT REP ' A"\5
PicBasic and PicBasic Pro programming 119
Table 4.13
LCD character table
^-^ Upper 4.
454= ^>^
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
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Example 4.1
A 2-row parallel LCD is connected to a PIC microcontroller as shown in Figure 4.9. Write a
PicBasic Pro program to display the string "PIC ROW 1" and "PIC ROW 2" in row 1 and row 2
of the LCD, respectively.
1 20 PIC BASIC projects
Solution 4.1
The required program is
PAUSE 1000
LCDOUT$FE,l
LCDOUT 'TIC ROW 1"
LCDOUT $FE, $C0
LCDOUT "PIC ROW 2"
' Wait 1 second for initialization
' Clear the LCD
' Display message in row 2
' Move cursor to row 2
' Display message in row 2
4.3.2 Serial LCDs
A serial LCD is connected to a microcontroller using only one data line. Both PicBasic and PicBasic
Pro languages can be used to send data to serial LCDs using the SEROUT command.
A popular serial LCD is the ILM-216 (see Figure 4.10). This is a 16-pin, 2-row by 16-character
LCD manufactured by Scott Edwards Electronics Inc. The device can operate with a baud rate of
2400 or 9600. In addition to the normal display functions, inputs for four push-button switches
and also an output to drive a buzzer are included on the LCD module. The module incorporates
an EEPROM memory and a backlight which are programmable.
Figure 4.10 ILM-2 1 6 serial LCD
Table 4.14 shows the pin configuration of this LCD. Pins 1 and 2 are the ground and the +5 V
supply connections, respectively. Pin 3 is the serial input pin. Either RS232 voltage levels or
standard TTL level signals can be connected to this pin. Similarly, pin 4 is the serial output pin
PicBasic and PicBasic Pro programming 121
and TTL logic levels (inverted) can be connected to this pin. Pin 5 is the buzzer out pin where a
small buzzer (up to 25 mA) can be connected to this pin and the buzzer can be controlled with the
software. Pins 6 to 8 are the option pins. Pin 7 is used to configure the device. Pin 8 is used to
select a baud rate and when this pin is connected to pin 6, the device operates at 9600 baud.
Leaving pin 8 unconnected configures the device to operate at 2400 baud. Pins 9 to 16 are four
push-button switch inputs. The state of these pins can be read from the software.
Table 4.14 Pin configuration of ILM-216
Pin No
Function
1
Ground
2
+5V
3
Serial in
4
Serial out
5
Bell
6
Ground
7
Config/test
8
9600 baud
9
Switch 1
10
Switch 1 ground
11
Switch 2
12
Switch 2 ground
13
Switch 3
14
Switch 3 ground
15
Switch 4
16
Switch 4 ground
The ILM-216 can be connected to a microcontroller using the following minimum pins:
Pin 1 ground
Pin 2 + 5 V supply
Pin 3 to microcontroller serial output
Pin 4 to microcontroller serial input (if it is required to read the state
of push-button switches on the LCD module)
The default factory configuration of the ILM-216 is 2400 baud, 8 data bits, no parity, and 1 stop
bit. Table 4. 15 gives a list of the control codes of ILM-216. These codes are summarized below:
Null: These characters are ignored by the LCD
1 22 PIC BASIC projects
Table 4.15 ILM-216 LCD control codes
Function
ASCII Code
Null
Cursor home
1
Hide cursor
4
Show underline cursor
5
Show blinking cursor
6
Bell
7
Backspace
8
Horizontal tab
9
Smart line feed
10
Vertical tab
11
Clear screen
12
Carriage return
13
Backlight on
14
Backlight off
15
Cursor position
16
Format right-aligned text
18
Escape codes
27
Cursor home: Moves the cursor to the first character position of the first row
Hide cursor: Hides the cursor so that it is not visible
Show underlined cursor: Shows a non-blinking underlined cursor at the current position
Show blinking cursor: Shows a blinking cursor at the current position
Bell: sends pulses to a buzzer connected to pin 5 of the LCD
Backspace: Moves the cursor back by one space and erases the character in that position
Smart line feed: Moves the cursor down by one line
Vertical tab: Moves the cursor up by one line
Clear screen: Clears the LCD screen
Carriage return: Moves the cursor to the first position on the next row
PicBasic and PicBasic Pro programming 123
Backlight on: Turns on the LED backlight
Backlight off: Turns off the LED backlight
Position cursor: Accepts a number from to 31 and moves the cursor to that position where
is the first character of the first row and 3 1 is the last character of the second row. Number 64
should be added to the required cursor position in order to get the actual displayed cursor posi-
tion. For example, position 80 corresponds to the first character position in the second row
(64 + 16 = 80).
Right align text: Accepts a number from 2 to 9 representing the width of an area on the screen in
which right-aligned text is to be displayed.
Escape sequences: Escape codes enable the user to define a custom character, to transfer data
from the EEPROM, and to read the state of the four push-button switch positions on the LCD
module.
Example 4.2
An ILM-216 model serial LCD is connected to bit of PORTB of a PIC microcontroller as shown
in Figure 4.11. Write a PicBasic Pro program to clear the LCD screen and then to display the
string "PIC LCD" in row 1 of the LCD. Wait 1 s for the initialization of the LCD.
+5V
14.7K
VDD
MCLR
RBO
RB3
I
3
ILM-216
Serial LCD
1
RAO PIC
RA1
RA2
Vss
RA3
OSC1 OSC2
— —
(
:i-
dD
K
L C2
ifT 4MHz ~F:
Figure 4.11 Connecting ILM-216 model LCD to a PIC microcontroller
1 24 PIC BASIC projects
Solution 4.2
The required program is given below. The PicBasic command SEROUT is used to send data to the
serial LCD.
PAUSE 1000 ' Wait 1 s for initialization
SEROUT PORTB.0, N2400 (12, "PIC LCD")
4.4 Interrupts
Interrupts are very useful in many microcontroller applications. An interrupt, as the name sug-
gests, interrupts the normal execution of a program and jumps to a designated address in the pro-
gram memory called the Interrupt Service Routine (ISR) where a short program is executed. At
the end of this program, control is returned to the main program and execution continues from the
point it was interrupted.
Interrupts are asynchronous events and it is not known when they may occur. There are basically
two types of interrupts: external interrupts and internal interrupts. External interrupts may occur
when an external event occurs. For example, when an external signal changes its state. Internal
interrupts are usually in the form of timer interrupts and an interrupt may be generated when the
timer overflows.
When an interrupt occurs, the PIC microcontroller saves the address of the next instruction on
stack and jumps to the ISR which is at address 4 of the program memory. When interrupts are
expected from multiple sources, the program should check at the beginning of the ISR to deter-
mine the actual source of the interrupt.
PicBasic Pro allows the use of interrupts in programs. The command
ON INTERRUPT GOTO Label
declares Label as the starting point of the ISR. Further interrupts should be disabled by the
DISABLE command just before entering the ISR. Also, further interrupts should be enabled by
the ENABLE command after the end of the ISR. The last statement in the ISR should be the
RESUME statement which terminates the ISR and returns to the main program.
The structure of the main program and the ISR are as follows:
Main program
ON INTERRUPT GOTO Mylabel
PicBasic and PicBasic Pro programming 125
Interrupt Service Routine
DISABLE
Mylabel:
RESUME
ENABLE
The use of external and timer interrupts will be discussed further with examples in the projects
section of this book.
4.5 Recommended PicBasic Pro program structure
A PicBasic Pro program can be written in many different formats. The author recommends that
you use a template similar to the one given in Figure 4.12 when developing PicBasic Pro pro-
grams. As you can see in this figure, the header includes a brief description of the program includ-
ing the author name, the date, and filename of the program. Comments are used in every line of
the program to clarify the actions of the program.
LED FLASHING PROGRAM
This program flashes and LED connected to port RBO of PORTB.
The Led is flashed with 1 second intervals.
Author:
Dogan Ibrahim
Date:
September, 2005
File:
LED.PBP
Modifications
Figure 4.12 (Continued)
1 26 PIC BASIC projects
1 DEFINITIONS
LED VAR PORTB.O
' Define RBO as LED
' START OF MAIN PROGRAM
TRISB =
AGAIN:
LED= 1
PAUSE 1000
LED =
PAUSE 1000
GOTO AGAIN
' Set PORT B pins as outputs
' Turn ON LED
' Wait 1 second
' Turn OFF LED
' Wait 1 second
' Repeat
END ' End of program
Figure 4.12 Recommended PicBasic Pro program template
4.6 Using stepping motors
Stepping motors are widely used in many microcontroller-based projects where motion is required.
This section describes the basic operation of these motors and also shows how they can be used
in microcontroller-based projects with PicBasic and PicBasic Pro languages.
Stepping motors are electro-mechanical devices that convert electrical pulses into discrete
mechanical movements. A conventional motor has a free running shaft and rotates continuously
as long as power is applied to the motor. The shaft of a stepping motor rotates in discrete steps
when electrical pulses are applied to it in the correct sequence. The speed of the rotation is related
to the time between the input pulses and the length of rotation is directly related to the number of
pulses applied. Basically, the motor rotates by an angle defined as the "stepping angle" each time
a pulse is applied to the motor. For example, if the stepping angle of a stepping motor is specified
as 10°, then each time a pulse is applied the motor will rotate by an angle of 10° and 36 pulses
will be required to make a complete 360° rotation.
Stepping motors have the following advantages over the conventional motors:
• Motor shaft position can be controlled very accurately using pulses and in open-loop mode.
• Stepping motors can be operated at very low speeds.
PicBasic and PicBasic Pro programming 127
• Stepping motors are very reliable since there are no brushes and, as a result, these motors have
very long operational lives.
• Stepping motors have full torque at standstill.
• The speed of stepping motors can be controlled easily and accurately.
There are basically two types of stepping motors: unipolar and bipolar. Unipolar motors are easy
to control where two windings with common points are used, and a simple 1-of-n counter circuit
can be used to generate the required stepping sequence. A driver transistor can be used for each
winding. One of the most commonly used drive methods is 1 phase full step, also known as the
"wave drive", where the motor windings are energised one at a time as shown in Table 4.16. The
motor can be driven by using a MOSFET power transistor for each coil winding, as shown in
Figure 4.13. Unipolar motors can also be driven by using integrated circuits, such as the
UCN5804B. This chip operates with voltages between 6 and 30 V. It contains a CMOS logic sec-
tion for the sequencing logic and a high-voltage output section to directly drive a unipolar step-
ping motor. As shown in Figure 4.14, the motor is connected directly to the chip and the chip
Table 4.16 One-phase full- step drive
Step
A
B
c
D
1
1
2
1
3
1
4
1
ob
88
To stepping motor
Figure 4.13 Driving a unipolar stepping motor
1 28 PIC BASIC projects
Q+V
Q+V
16
14
11
DIR
VDD
UCN5804B
STEP
OutB
Kbd
OutD
OutC
Kac
OutA
M I Stepping motor
nxKxn
Figure 4.14 Controlling a unipolar motor using a UCN5804B
generates the correct sequence of signals to drive the motor. The DIR input controls the direction
of rotation. The motor is rotated by one step each time a pulse is applied to the STEP input.
Bipolar motors generally produce higher torques, but more complex circuits are required to con-
trol these motors. The control of bipolar stepping motors is beyond the scope of this book.
Figure 4.15 shows a typical small stepping motor.
Figure 4.15 A typical stepping motor
4.7 Using servomotors
Servomotors are generally used in radio control toys, such as airplanes, boats, or robots. A servo-
motor consists of a DC motor with a series of gears attached to it. An internal potentiometer is
used with feedback to control the movement of the motor. Normally, the output shaft is limited to
180° of rotation, but it is possible to modify a servomotor so that continuous rotation is obtained.
In the projects section of this book, we shall be looking at the control of modified servomotors.
PicBasic and PicBasic Pro programming 129
A servomotor is controlled with pulse-width-modulated (PWM) signal. In a modified servo-
motor, a pulse with a width of 2 ms rotates the motor clockwise at full speed. Similarly, a pulse
with a width of 1 ms rotates the motor anti-clockwise at full speed. Sending a pulse with a width
of 1 .5 ms stops the motor.
A servomotor requires only three wires to operate: +V, ground, and the signal wire where the
pulse is applied.
Figure 4.16 shows a typical small servomotor.
Figure 4.16 A typical servomotor
4.8 Exercises
1. What are the ranges of PicBasic variables bit, byte and word?
2. Explain how you can declare a 20-element byte array called scores in PicBasic.
3. Explain how you can use comments in PicBasic and PicBasic Pro programs. Why should we
use comments in our programs?
4. Why would you use Symbols in a PicBasic program?
5. Explain the use of the command BRANCH by giving an example.
6. Give different ways in which you can make loops in PicBasic Pro programs.
7. Explain how you can connect an LCD to a PIC microcontroller using the default settings.
8. Write a program to count from to 100 repeatedly with 1 s intervals and show your results
on a parallel LCD.
9. Explain the advantages and the disadvantages of parallel and serial LCDs.
10. Write a PicBasic Pro program to display the text "RESULTS" in row 1, column 5 of a paral-
lel LCD.
1 1 . Write a PicBasic Pro program to count from to 100 in steps of 2 and show the output on the
second row of a parallel LCD.
12. Repeat question 1 1 using a serial LCD and PicBasic language.
13. Explain how you can use the DEFINE statements to change the interface between a PIC
microcontroller and an LCD.
1 30 PIC BASIC projects
14. Give an example for the use of the SELECT.. CASE command. Show how you can program
using the IE. THEN.. ELSE command instead. Explain which one you would prefer.
15. Explain the differences between the REPEAT..UNTIL and WHILE..WEND commands. Give
examples for each command.
16. Explain how a unipolar stepping motor can be controlled.
17. Explain how a modified servomotor can be controlled to rotate: (a) full speed clockwise,
(b) full speed anti-clockwise.
5
PicBasic and PicBasic Pro
projects
In previous chapters we have seen the characteristics of the PIC microcontrollers and how to pro-
gram these microcontrollers using the PicBasic and PicBasic Pro languages. In this chapter we
shall be looking at various PIC microcontroller-based projects. All the projects described here
have been constructed and tested using both the PicBasic and PicBasic Pro languages.
Each project has been described with the following sub-headings:
Project title:
Title of the project
Project description: A brief description of the project.
Hardware:
Flow diagram:
Software:
Hardware used in the project. This is mainly the circuit diagram of the
microcontroller and associated interface electronics used for the project.
A flow diagram is given to describe the operation of the project.
Listings of the microcontroller programs for both PicBasic and PicBasic
Pro languages.
Projects in this chapter have been organised in increasing complexity. It is recommended that the
reader study the simple projects first before going to the more complex ones.
1 32 PIC BASIC projects
Project 1
Project title:
Simple flashing LED
Project description: An LED is connected to one of the port pins of a PIC microcontroller. The
LED is flashed continuously with 1-s interval.
Hardware:
This project is so simple that any type of PIC microcontroller can be used.
As shown in Figure 5.1, a PIC16F84 type microcontroller is chosen for
this project. Bit of PORTB (RBO) is connected to a small LED through
a current-limiting resistor. The voltage drop across an LED is approxi-
mately 2 V. Assuming an LED current of 10 mA, the value of the resistor
can be calculated as
I
5-2
10mA
= 0.3K
the nearest value is 33011.
9 V ; o.33 mf= =
Battery ^
78L05
Figure 5.1 Circuit diagram of Project 1
Flow diagram:
The project has been constructed on a breadboard as shown in Figure 5.2.
The software consists of an indefinite loop where the LED is turned on
and off inside this loop. The flow diagram of the software is shown in
Figure 5.3.
PicBasic and PicBasic Pro projects 133
Figure 5.2 Construction of Project 1
C BEGIN J
i
'
Set port directions
i
f
Turn on LED
i
'
Wait for 1 second
i
'
Turn off LED
i
'
Wait for 1 second
.
.
Figure 5.3 Flow diagram of Project 1
Software:
PicBasic
The software for PicBasic language is shown in Figure 5.4. At the begin-
ning of the program LED is defined as a symbol and is assigned to zero
(bit of PORTB). Also, the port direction register TRISB and PORTB
1 34 PIC BASIC projects
addresses are defined. The main program is an indefinite loop and starts
with label AGAIN. Inside the main program the LED is turned on using
the HIGH LED instruction. Then after a delay of 1 s (PAUSE 1000) the
LED is turned off and this process is repeated forever.
LED FLASHING PROGRAM
This program flashes an LED connected to port RBO of PORTB. The
Led is flashed with 1 second intervals.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
LED1.BAS
Modifications
SYMBOLS
Symbol LED =
Symbol TRISB = $86
Symbol PORTB = $06
' START OF MAIN PROGRAM
POKE TRISB,
' Define RBO as LED
' TRISB address
' PORTB address
AGAIN:
HIGH LED
PAUSE 1000
LOW LED
PAUSE 1000
GOTO AGAIN
END
Figure 5.4 PicBasic program of Project 1
' Set PORTB pins as outputs
' Turn ON LED
' Wait 1 second
' Turn OFF LED
' Wait 1 second
' Repeat
' End of program
PicBasic and PicBasic Pro projects 135
PicBasic Pro
The software for PicBasic Pro language is shown in Figure 5.5. At the
beginning of the program LED is defined as bit of PORTB (PORTB.O).
Port direction register TRISB is then cleared so that all PORTB pins are
outputs. Main program starts with label AGAIN where the port pin is
turned on and off with 1 s intervals.
LED FLASHING PROGRAM
This program flashes an LED connected to port RBO of PORTB. The
LED is flashed with 1 second intervals.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED2.BAS
Modifications
DEFINITIONS
LED VAR PORTB.O
START OF MAIN PROGRAM
TRISB =
' Define RBO as LED
' Set PORTB pins as outputs
AGAIN:
LED = 1
PAUSE 1000
' Turn ON LED
' Wait 1 second
LED =
PAUSE 1000
' Turn OFF LED
' Wait 1 second
GOTO AGAIN
END
Figure 5.5 PicBasic Pro program of Project 1
' Repeat
' End of program
1 36 PIC BASIC projects
Using a different microcontroller
In this project a PIC16F84-type microcontroller has been used. Recently, PIC16F627 has become
one of the popular low-cost PIC microcontrollers. This is an 18-pin microcontroller, pin compat-
ible with the PIC16F84, having 16 I/O ports and built-in 4-MHz-clock oscillator. In this section
we shall be using the PIC16F627 to flash the LED.
Figure 5.6 shows the circuit diagram of the PIC16F627-based project. The LED is connected to
bit of PORTB as in Figure 5.1 and the internal oscillator of the microcontroller is used.
jy \ 0.33 MFzz
Battery \ ^
i
78L05
+5V
Figure 5.6 Circuit diagram of the PIC 1 6F627 -based project
Figure 5.7 shows the construction of the project on a breadboard. Notice that there are no timing
components in this circuit.
Figure 5.7 Construction of the project on a breadboard
PicBasic and PicBasic Pro projects 1 37
PicBasic and PicBasic Pro programs of the project are same as in Figures 5.4 and 5.5, respect-
ively. The internal 4-MHz-clock oscillator should be selected during programming of the micro-
controller as shown in Figure 5.8.
OK
Fuse value 3FT9H
f" Code Protect
r INTRCRA6-I0
|" Data Protect
r ec
I - Low Volts Program
r hs
r~ Brown Out Enable
txt
r MCLR En
r lp
Power Up Timer
r Watch Dog
r ER RA6-CK0
r ER RA6-I0
17 INTRCRA6-CK0
Cancel
Clear Fuses
Help
Figure 5.8 Selecting the internal 4 MHz oscillator during programming
138 PIC BASIC projects
Project 2
Project title:
Complex flashing LED
Project description: An LED is connected to one of the port pins of a PIC microcontroller. The
LED is flashed continuously as in the following sequence:
3 flashes with 250ms interval between each flash.
2 s delay.
3 flashes with 250ms interval between each flash.
Hardware:
Flow diagram:
Software:
The hardware of this project is same as in Figure 5.6. A PIC16F627 micro-
controller is used in this project with built-in 4 MHz oscillator and an LED
is connected to bit of PORTB using a 330 fl current-limiting resistor.
The software consists of an indefinite loop where the LED is turned on
and off as described in the project description. The flow diagram of the
software is shown in Figure 5.9.
PicBasic
The software for PicBasic language is shown in Figure 5. 10. At the begin-
ning of the program LED is defined as a symbol and is assigned to zero
(bit of PORTB). Also, the port-direction register TRISB and PORTB
addresses are defined. The main program is an indefinite loop and starts
with label AGAIN. Inside the main program a OR loop is formed and the
LED is flashed three times with 250ms intervals. After a 2s delay the
process is repeated. Variable Cnt is used as the loop-count variable.
PicBasic Pro
The software for PicBasic Pro language is shown in Figure 5.11. At the
beginning of the program port-direction register TRISB is cleared so that
all PORTB pins are outputs. Main program starts with label AGAIN.
Inside the main program a FOR loop is formed and the LED is flashed
three times with 250 ms intervals. After a 2 s delay the process is repeated.
Variable Cnt is used as the loop-count variable.
PicBasic and PicBasic Pro projects 139
BEGIN
v
Set port directions
i '
1 =0
Y
^ '
Turn on LED
v
Wait for 250ms
i
Turn off LED
V
Wait for 250ms
i
'
1 = 1 + 1
3 /^
Wait for 2 seconds
i
'
Figure 5.9 Flow diagram of Project 2
LED FLASHING PROGRAM
This program flashes an LED connected to port RBO of PORTB. The
LED is flashed continuously as follows:
Flash 3 times with 250ms intervals
Wait 2 seconds
Figure 5.10 (Continued)
1 40 PIC BASIC projects
Flash 3 times with 250ms intervals
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
LED3.BAS
Modifications
AGAIN:
FOR Cnt = 1 TO 3
HIGH LED
PAUSE 250
LOW LED
PAUSE 250
NEXT Cnt
PAUSE 2000
GOTO AGAIN
END
Figure 5.10 PicBasic program of Project 2
' Define RB0 as LED
' TRISB address
' PORTB address
SYMBOLS
Symbol LED =
Symbol TRISB = $86
Symbol PORTB = $06
' VARIABLES
Symbol Cnt = B0
' START OF MAIN PROGRAM
POKE TRISB,
' Declare Cnt as a byte
' Set PORTB pins as outputs
' Turn ON LED
' Wait 250ms
' Turn OFF LED
' Wait 250ms
' Wait 2 seconds
' Repeat
' End of program
PicBasic and PicBasic Pro projects 141
LED FLASHING PROGRAM
This program flashes an LED connected to port RBO of PORTB. The
LED is flashed continuously as follows:
Flash 3 times with 250ms intervals
Wait 2 seconds
Flash 3 times with 250ms intervals
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED4.BAS
Modifications
' Declare Cnt as a byte
DEFINITIONS
Cnt VAR BYTE
START OF MAIN PROGRAM
TRISB =
AGAIN:
FOR Cnt = 1 TO 3
PORTB. = 1
PAUSE 250
PORTB. =
PAUSE 250
NEXT Cnt
PAUSE 2000
GOTO AGAIN
END
Figure 5.11 PicBasic Pro program of Project 2
' Set PORTB pins as outputs
' Turn ON LED
' Wait 250ms
' Turn OFF LED
' Wait 250ms
' Wait 2 seconds
' Repeat
' End of program
1 42 PIC BASIC projects
Project 3
Project title:
Flashing LED warning lights
Project description: In this project, two LEDs are connected to bit of PORTB of a PIC
microcontroller. The LEDs turn on and off alternately with 1 s delay.
Hardware:
The hardware of this project is similar to the circuit given in Figure 5.6.
But here, two LEDs are connected to the same output pin of the microcon-
troller. When the pin output is logic 1, the microcontroller is sourcing cur-
rent and the lower LED is turned on and the upper LED is off. Similarly,
when the pin output is logic 0, the microcontroller is sinking current and
the upper LED is turned on and the lower LED is off. 330 H current- limiting
resistors are used for each LED. The circuit diagram of the project is
shown in Figure 5.12.The construction of the project on a breadboard is
shown in Figure 5.13.
+5V
jy ! 0.33 MF-z
Battery |
LED
Figure 5.12 Circuit diagram of Project 3
Flow diagram:
The flow diagram of the project is as in Figure 5.3, i.e. the output pin of
the microcontroller is turned on and off with 1 s intervals.
Software:
PicBasic
The software for PicBasic language is exactly same as given in Figure 5.4.
PicBasic Pro
The software for PicBasic Pro language is exactly same as given in Figure 5.5.
PicBasic and PicBasic Pro projects 143
Figure 5.13 Construction of the project on a breadboard
1 44 PIC BASIC projects
Project 4
Project title:
Project description:
Hardware:
Turning on odd numbered LEDs
In this project, 8 LEDs are connected to PORTB of a PIC microcontroller.
When the project is started (or when reset), only the odd numbered
LEDs turn on (i.e. the LEDs connected to bit 1, bit 3, bit 5, and bit 7 of
PORTB).
The circuit diagram of the project is shown in Figure 5.14. A PIC16F627
model PIC microcontroller is used and the microcontroller is operated from
its 4 MHz internal clock. The LEDs are connected to 8 pins of PORTB
using 330 11 current-limiting resistors. An external reset button is connected
to MCLR input of the microcontroller.
9V ; 0.33 M F= =
Battery ] M ^
LEDs
6 330 £
Figure 5.14 Circuit diagram of Project 4
Flow diagram:
The construction of the project on a breadboard is shown in Figure 5.15.
The flow diagram of the project is shown in Figure 5.16. At the beginning
of the program the I/O direction is specified. And then the hexadecimal
number $AA is sent to PORTB to turn on the odd-numbered LEDs. Note
that
$AA = 10101010
PicBasic and PicBasic Pro projects 145
Figure 5.15 Construction of the project on a breadboard
BEGIN
Set port directions
Send $AA to
PORTB
END
Figure 5.16 Flow diagram of Project 4
i.e. the odd numbered bit positions are logic 1, and even-numbered bit
positions are logic 0.
Software:
PicBasic
The software for PicBasic language is given in Figure 5. 17. At the begin-
ning of the program PORTB and TRISB addresses are defined. TRISB is
then cleared to to make all PORTB pins as outputs. Then the hexadeci-
mal number $AA is sent to PORTB using the POKE statement to turn on
the odd-numbered LEDs.
1 46 PIC BASIC projects
TURN ON ODD NUMBERED LEDS
This program turns on odd numbered LEDs (bit 1, bit 3, bit 5, bit 7) connected
to PORTB of a PIC16F627 microcontroller.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
LED5.BAS
Modifications
SYMBOLS
Symbol TRISB = $86
Symbol PORTB = $06
' TRISB address
' PORTB address
' START OF MAIN PROGRAM
POKE TRISB,
POKE PORTB, $AA
END
Figure 5.17 PicBasic program of Project 4
' Set PORTB pins as outputs
' Turn on odd numbered LEDs
' End of program
PicBasic Pro
The software for PicBasic Pro language is given in Figure 5.18. At the
beginning of the program TRISB is cleared to to make all PORTB pins
as outputs. Then the hexadecimal number $AA is sent to PORTB to turn
on the odd-numbered LEDs.
PicBasic and PicBasic Pro projects 147
TURN ON ODD NUMBERED LEDS
This program turns on odd numbered LEDs (bit 1, bit 3, bit 5, bit 7) connected
to PORTB of a PIC16F627 microcontroller.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED6.BAS
Modifications
DEFINITIONS
START OF MAIN PROGRAM
TRISB =0 'Set PORTB pins as outputs
PORTB = $AA ' Turn on odd numbered LEDs
END ' End of program
Figure 5.18 PicBasic Pro program of Project 5
1 48 PIC BASIC projects
Project 5
Project title:
Project description:
Binary counting LEDs
In this project, 8 LEDs are connected to PORTB of a PIC microcontroller.
When the project is started (or when reset), the LEDs count in binary with
a 250 ms delay between each count as shown in Figure 5.19. The count
goes from (binary "00000000") to 255 (binary "11111111") and then
repeats forever.
ooooooo
ooooooto
OOOOOOft
oooootoo
oooootot
OOOOOIIO
oooooooo
ooooooo
Figure 5.19 Binary counting LEDs
Hardware:
Flow diagram:
The circuit diagram and the construction of the project are as in Figures
5.14 and 5.15, respectively. A PIC16F627 model PIC microcontroller is
used and the microcontroller is operated from its 4 MHz internal clock. The
LEDs are connected to 8 pins of PORTB using 33011 current-limiting
resistors. An external reset button is connected to MCLR input of the
microcontroller.
The flow diagram of the project is shown in Figure 5.20. At the beginning
of the program the I/O direction is specified. A byte variable called Cut is
used as the loop variable and it is incremented by one every 250 ms. When
Cnt reaches 255 it overflows and takes the next value and this process is
repeated forever.
PicBasic and PicBasic Pro projects 149
C BEGIN J
V
Set port directions
^ '
Cnt =
V
Send Cnt to
PORTB
t
250ms Delay
i
'
Cnt = Cnt + 1
'
r
Figure 5.20 Flow diagram of Project 5
Software:
PicBasic
The software for PicBasic language is given in Figure 5.21. At the begin-
ning of the program PORTB and TRISB addresses are defined. TRISB is
then cleared to to make all PORTB pins as outputs. Then variable Cnt is
initialised to zero. Inside the program loop the value of Cnt is sent to
PORTB and then incremented by one. This loop is repeated forever.
BINARY COUNTING LEDS
8 LEDs are connected to PORTB of a PIC microcontroller. This program
counts in binary and displays the result on the LEDs with 250ms delay
between each count.
Author: Dogan Ibrahim
Date: October, 2005
Figure 5.21 (Continued)
1 50 PIC BASIC projects
Compiler:
PicBasic
File:
LED7.BAS
Modifications
SYMBOLS
Symbol TRISB = $86
Symbol PORTB = $06
Symbol Cnt = BO
' START OF MAIN PROGRAM
POKE TRISB,
LOOP:
POKE PORTB, Cnt
PAUSE 250
Cnt = Cnt +1
GOTO LOOP
END
Figure 5.21 PicBasic program of Project 5
' TRISB address
' PORTB address
' Cnt is a byte variable
' Set PORTB pins as outputs
' Send Cnt to PORTB
' Wait 250ms
' Increment Cnt
' Repeat
' End of program
PicBasic Pro
The software for PicBasic Pro language is given in Figure 5.22. At the
beginning of the program TRISB is cleared to to make all PORTB pins
as outputs. Then variable Cnt is initialised to zero. Inside the program
loop the value of Cnt is sent to PORTB and then incremented by one.
Variable Cnt is a byte and increments from to 255 and then overflows
back to 0. The loop is repeated forever.
BINARY COUNTING LEDS
8 LEDs are connected to PORTB of a PIC16F627 microcontroller.
This program counts in binary and displays the result on the LEDs. A
250ms delay is used between each count.
Figure 5.22 (Continued)
PicBasic and PicBasic Pro projects 151
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED8.BAS
Modifications
' Declare Cnt as a Byte variable
DEFINITIONS
Cnt VAR Byte
START OF MAIN PROGRAM
TRISB =
Cnt =
LOOP:
PORTB = Cnt
PAUSE 250
Cnt = Cnt + 1
GOTO LOOP
END
Figure 5.22 PicBasic Pro program of Project 5
' Set PORTB pins as outputs
' Initialise Cnt to
' Send Cnt to PORTB
' 250ms delay
' Increment Cnt
' Repeat
' End of program
1 52 PIC BASIC projects
Project 6
Project title:
Project description:
Left scrolling LEDs
In this project, 8 LEDs are connected to PORTB of a PIC microcontroller.
When the project is started (or when reset), the LEDs scroll to the left
with a 250ms delay between each output as shown in Figure 5.23. When
the left-most LED (bit 7) is lit, the next LED lit is the right-most LED (bit
0). This process is repeated forever.
ooooooot
ooooooto
oooootoo
0000*000
oootoooo
ootooooo
otoooooo
•ooooooo
ooooooot
Figure 5.23 Left scrolling LEDs
Hardware:
The circuit diagram and the construction of the project are as in Figures
5.14 and 5.15, respectively. A PIC16F627 model PIC microcontroller is
used and the microcontroller is operated from its 4 MHz internal clock. The
LEDs are connected to 8 pins of PORTB using 33011 current-limiting
resistors. An external reset button is connected to MCLR input of the
microcontroller.
Flow diagram:
The flow diagram of the project is shown in Figure 5.24. At the beginning
of the program the I/O direction is specified. A byte variable called Cut is
used as the loop variable and it is shifted left by one digit at every iteration
of the loop. When the value of Cnt is 128 (left-most LED is on), it is re-
initialised back to 1 . A 250 ms delay is used between each output.
PicBasic and PicBasic Pro projects 153
f BEGIN J
v
Set port directions
i
'
Cnt = 1
r
i
Send Cnt to
PORTB
^
250ms Delay
Left shift Cnt
jr
A
k
N
s. unt —
Y
Figure 5.24 Flow diagram of Project 6
Software:
PicBasic
The software for PicBasic language is given in Figure 5.25. At the begin-
ning of the program PORTB and TRISB addresses are defined. TRISB is
then cleared to to make all PORTB pins as outputs. Then variable Cnt is
initialised to 1 and its value is sent to PORTB to turn on the right-most LED
(bit 0). Inside the program loop the value of Cnt is shifted left one digit by
multiplying with 2 so that the next higher LED can be turned on. When the
left- most LED (bit 7) is turned on the value of Cnt is 128 and it is
re-initialised to 1 so that the next LED to be turned on is the first LED (bit
0). This loop is repeated forever with 250 ms delay between each output.
LEFT SCROLLING LEDS
8 LEDs are connected to PORTB of a PIC microcontroller. This program
scrolls the LEDs to the left by one digit. When the LED at bit 7 is turned
on, then the next LED to be turned on is the LED at bit position 0. The
program loop is repeated with 250ms delay between each loop.
Figure 5.25 (Continued)
1 54 PIC BASIC projects
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
LED9.BAS
Modifications
SYMBOLS
Symbol TRISB = $86
Symbol PORTB = $06
Symbol Cnt = BO
' START OF MAIN PROGRAM
POKE TRISB,
INIT:
CNT = 1
' TRISB address
' PORTB address
' Cnt is a byte variable
' Set PORTB pins as outputs
' Initialise Cnt to 1
LOOP:
POKE PORTB, Cnt
PAUSE 250
IF Cnt = 128 THEN INIT
Cnt = Cnt * 2
GOTO LOOP
END
Figure 5.25 PicBasic program of Project 6
' Send Cnt to PORTB
' Wait 250ms
' IF the left-most LED
' Left-shift Cnt by 1 digit
' Repeat
' End of program
PicBasic Pro
The software for PicBasic Pro language is given in Figure 5.26. At the begin-
ning of the program TRISB is cleared to to make all PORTB pins as out-
puts. Then variable Cnt is initialised to 1 and its value is sent to PORTB to
turn on the right-most LED (LED at bit position 0). Inside the program loop
the value of Cnt is shifted left one digit by using the shift operator "«" so
that the next higher LED can be turned on. When the left-most LED (bit 7)
is turned on the value of Cnt is 128 and it is re- initialised to 1 for the next
loop. This loop is repeated forever with a 250 ms delay between each output.
PicBasic and PicBasic Pro projects 155
LEFT SHIFTING LEDS
8 LEDs are connected to PORTB of a PIC16F627 microcontroller.
This program scrolls the LEDs left with 250ms delay between each
output. When the LED at bit 7 is on, the next LED to be on is the
one at bit position 0.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED10.BAS
Modifications
DEFINITIONS
CntVARByte
START OF MAIN PROGRAM
' Declare Cnt as a Byte variable
TRISB =
INIT:
Cnt=l
LOOP:
PORTB = Cnt
PAUSE 250
IF Cnt =128 THEN INIT
Cnt = Cnt « 1
GOTO LOOP
END
Figure 5.26 PicBasic Pro program of Project 6
' Set PORTB pins as outputs
' Initialise Cnt to 1
' Send Cnt to PORTB
' Wait 250ms
' If the left-most LED
' Left-shift Cnt by 1 digit
' Repeat
' End of program
1 56 PIC BASIC projects
Project 7
Project title:
Project description:
Right scrolling LEDs
In this project, 8 LEDs are connected to PORTB of a PIC microcontroller.
When the project is started (or when reset), the LEDs scroll to the right
with a 250ms delay between each output as shown in Figure 5.27. When
the right-most LED (bit 0) is lit, the next LED lit is the left-most LED (bit
7). This process is repeated forever.
•ooooooo
otoooooo
OOIOOOOO
oootoooo
0000*000
00000*00
oooooo*o
ooooooo*
•ooooooo
Figure 5.27 Right scrolling LEDs
Hardware:
The circuit diagram and the construction of the project are as in Figures 5.14
and 5.15, respectively. A PIC16F627 model PIC microcontroller is used
and the microcontroller is operated from its 4 MHz internal clock. The
LEDs are connected to 8 pins of PORTB using 33011 current-limiting
resistors. An external reset button is connected to MCLR input of the
microcontroller.
Flow diagram:
The flow diagram of the project is shown in Figure 5.28. At the beginning
of the program the I/O direction is specified. A byte variable called Cut is
used as the loop variable and it is shifted right by one digit at every iter-
ation of the loop. When the value of Cnt is 1 (the right-most LED is on), it
is re-initialised back to 128. A 250 ms delay is used between each output.
PicBasic and PicBasic Pro projects 157
C BEGIN J
^f
Set port directions
^
'
Cnt = 128
r
i
Send Cnt to
PORTB
"
250ms Delay
Right shift Cnt
i
k
N
<? Pnt "• ^ ^\
Y
Figure 5.28 Flow diagram of Project 7
Software:
PicBasic
The software for PicBasic language is given in Figure 5.29. At the beginning
of the program PORTB and TRISB addresses are defined. TRISB is then
cleared to to make all PORTB pins as outputs. Then variable Cnt is ini-
tialised to 128 and its value is sent to PORTB to turn on the left-most LED
(bit 7). Inside the program loop the value of Cnt is shifted right one digit by
dividing with 2 so that the next lower LED can be turned on. When the right-
most LED (bit 0) is turned on the value of Cnt is 1 and it is re-initialised to
128 so that the next LED to be turned on is the left-most LED (bit 7). This
loop is repeated forever with 250 ms delay between each output.
RIGHT SCROLLING LEDS
8 LEDs are connected to PORTB of a PIC microcontroller. This program
scrolls the LEDs to the right by one digit. When the LED at bit is turned
on, then the next LED to be turned on is the LED at bit position 7. The
program loop is repeated with 250ms delay between each loop.
Figure 5.29 (Continued)
158 PIC BASIC projects
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
LED 1 LB AS
Modifications
SYMBOLS
Symbol TRISB = $86
Symbol PORTB = $06
Symbol Cnt = BO
' START OF MAIN PROGRAM
' TRISB address
' PORTB address
' Cnt is a byte variable
POKE TRISB,
INIT:
CNT= 128
LOOP:
POKE PORTB, Cnt
PAUSE 250
IF Cnt = 1 THEN INIT
Cnt = Cnt / 2
GOTO LOOP
END
Figure 5.29 PicBasic program of Project 7
' Set PORTB pins as outputs
' Initialise Cnt to 128
' Send Cnt to PORTB
' Wait 250ms
' IF the right-most LED
' Right-shift Cnt by 1 digit
' Repeat
' End of program
PicBasic Pro
The software for PicBasic Pro language is given in Figure 5.30. At the begin-
ning of the program TRISB is cleared to to make all PORTB pins as out-
puts. Then variable Cnt is initialised to 128 and its value is sent to PORTB
to turn on the left-most LED (LED at bit position 7). Inside the program loop
the value of Cnt is shifted right one digit by using the shift operator "»" so
that the next lower LED can be turned on. When the right-most LED (bit 0)
is turned on the value of Cnt is 1 and it is re-initialised to 128 for the next
loop. This loop is repeated forever with a 250 ms delay between each output.
PicBasic and PicBasic Pro projects 159
RIGHT SHIFTING LEDS
8 LEDs are connected to PORTB of a PIC16F627 microcontroller.
This program scrolls the LEDs right with 250ms delay between each
output. When the LED at bit is on, the next LED to be on is the
one at bit position 7.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED12.BAS
Modifications
DEFINITIONS
CntVARByte
START OF MAIN PROGRAM
TRISB =
INIT:
Cnt= 128
LOOP:
PORTB = Cnt
PAUSE 250
IF Cnt = 1 THEN INIT
Cnt = Cnt » 1
GOTO LOOP
END
Figure 5.30 PicBasic Pro program of Project 7
' Declare Cnt as a Byte variable
' Set PORTB pins as outputs
' Initialise Cnt to 128
' Send Cnt to PORTB
' Wait 250ms
' If the right-most LED
' Right-shift Cnt by 1 digit
' Repeat
' End of program
1 60 PIC BASIC projects
Project 8
Project title:
Project description:
Hardware:
Right-left scrolling LEDs
In this project, 8 LEDs are connected to PORTB of a PIC microcontroller.
Also a push-button switch is connected to bit of PORTA using a pull-up
resistor. Normally the LEDs scroll to the left as in Project 6. When the
switch is pressed the LEDs scroll to the right as in Project 7.
The circuit diagram of the project is shown in Figure 5.31. The circuit is
very similar to Figure 5.14, but in this project additionally a switch is con-
nected to bit of PORTA to control the direction of scrolling. A PIC16F627
model PIC microcontroller is used and the microcontroller is operated from
its 4 MHz internal clock. The LEDs are connected to 8 pins of PORTB
using 330 H current-limiting resistors. An external reset button is con-
nected to MCLR input of the microcontroller.
9V
Battery
1
0.33 uF=b
78L05
^r
+5V
-nO-OlpF
14
4.7K
L
Push to
Reset
■d
[-— MCLR
+5V
4?k U
Push to j-TI
Scroll u
Right
Vdd
RBO
RB1
RB2
RB3
PIC RB4
16F627 RB5
RAO
RB6
RB7
Vss
Figure 5.31 Circuit diagram of Project 8
6 330
10
11
12
13
1
LEDs
B—
Flow diagram:
The flow diagram of the project is shown in Figure 5.32. At the beginning
of the program the I/O direction is specified. A byte variable called Cnt is
used as the loop variable. The program consists of an indefinite loop and
at the beginning of the loop the switch is tested. If the switch is logic 1
(i.e. switch is not pressed) then the scrolling is to the left and if the switch
is pressed the switch is at logic and scrolling is to the right. A 250 ms
delay is used between each output.
PicBasic and PicBasic Pro projects 161
BEGIN
Set port directions
Cnt = 1
Shift Cnt left
*+
Send Cnt to
PORTB
250ms Delay
Y
Figure 5.32 Flow diagram of Project 8
Shift Cnt right
Cnt = 128
Y
Software:
PicBasic
The software for PicBasic language is given in Figure 5.33. At the begin-
ning of the program PORTA, PORTB, TRISA, TRISB, and CMCON
register addresses are defined. TRISA is set to 1 so that bit of PORTA is
configured as an input port. Similarly, TRISB is cleared to so that all bits
of PORTB are configured as outputs. Push-button switch is connected to
bit of PORTA (RAO). Normally this pin is pulled high to logic 1 by using
a resistor. When the switch is pressed the pin goes down to logic 0. PORTA
pins on the PIC16F627 microcontroller have dual functions and they can
either be used as analog comparator inputs, or as digital I/O ports. CMCON
register is used to control the function of these pins. Setting CMCON to 7
configures PORTA pins as digital I/O ports.
Inside the LOOP, the value of Cnt is sent to PORTB and the PEEK instruc-
tion is used to read the switch setting. "BitO" refers to bit of variable
"BO" which is where the switch is connected. When the switch is pressed
the program jumps to label PRESSED where the LEDs are scrolled right.
When the switch is not pressed the LEDs are scrolled left. This loop is
repeated forever with 250 ms delay between each output.
1 62 PIC BASIC projects
RIGHT-LEFT SCROLLING LEDS
8 LEDs are connected to PORTB of a PIC microcontroller. This program
scrolls the LEDs to the right or left depending on a switch setting. The switch
is connected to bit of PORT A. If the switch is not pressed the switch
output is at logic 1 and the LEDs scroll to the left. When the switch is
pressed the LEDs scroll to the right. A 250ms delay is used between each
output.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
LED13.BAS
Modifications
SYMBOLS
Symbol TRISA = $85
Symbol TRISB = $86
Symbol PORTA = $05
Symbol PORTB = $06
Symbol CMCON = $1F
Symbol Cnt = Bl
Symbol Switch = B0
' TRISA address
' TRISB address
' PORTA address
' PORTB address
' CMCON address
' Cnt is a byte variable
' Switch is a byte variable
' START OF MAIN PROGRAM
POKE CMCON, 7
POKE TRISA, 1
POKE TRISB,
INIT:
CNT= 1
Figure 5.33 (Continued)
' RA0-RA3 are digital I/O
' Set PORTA bit as input
' Set all PORTB pins as outputs
' Initialise Cnt to 1
PicBasic and PicBasic Pro projects 163
LOOP:
POKE PORTB, Cnt
PAUSE 250
PEEK PORTA, Switch
IF BitO = THEN PRESSED
IF Cnt = 128 THEN INIT
Cnt = Cnt * 2
GOTO LOOP
PRESSED:
IF Cnt = 1 THEN NXT
Cnt = Cnt / 2
GOTO LOOP
NXT:
Cnt = 128
GOTO LOOP
END
Figure 5.33 PicBasic program of Project 8
' Send Cnt to PORTB
' Wait 250ms
' Read switch setting
' If switch is pressed
' Shift Cnt left
' Switch is pressed
' End of program
PicBasic Pro
The software for PicBasic Pro language is given in Figure 5.34. The
PicBasic Pro program is easier to understand. At the beginning of the pro-
gram TRISB is cleared to to make all PORTB pins as outputs. Also,
TRISA is set to 1 so that bit of PORTA is configured as input. CMCON
register is set to 7 to configure PORTA pins as digital I/O.
The switch setting is then checked using an IF statement. When the switch
is pressed bit of PORTA goes to logic and the program scrolls the
LEDs to right. When the switch is not pressed bit of PORTA is at logic
1 and the program scrolls the LEDs to the left.
RIGHT-LEFT SHIFTING LEDS
8 LEDs are connected to PORTB of a PIC16F627 microcontroller.
This program scrolls the LEDs right or left depending on the mode of a
push-button switch. When the switch is not pressed LEDs are scrolled left.
When the switch is pressed, LEDs are scrolled right. A 250ms delay
is used between each output.
Figure 5.34 (Continued)
1 64 PIC BASIC projects
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED14.BAS
Modifications
DEFINITIONS
CntVARByte
START OF MAIN PROGRAM
CMCON = 7
TRISA = 1
TRISB =
' Declare Cnt as a Byte variable
INIT:
Cnt = 1
' Set PORTA as digital I/O
' Set RAO as input
' Set PORTB pins as outputs
' Initialise Cnt to 1
' Send Cnt to PORTB
' Wait 250ms
LOOP:
PORTB = Cnt
PAUSE 250
IF PORTA.O = THEN
IF Cnt = 1 THEN Cnt =128: GOTO LOOP
Cnt = Cnt » 1 ' Shift right
GOTO LOOP
ELSE
IF Cnt = 128 THEN INIT
Cnt = Cnt « 1 ' Shift left
GOTO LOOP
ENDIF
END ' End of program
Figure 5.34 PicBasic Pro program of Project 8
PicBasic and PicBasic Pro projects 165
Project 9
Project title:
Project description:
LED dice
In this project, 7 LEDs are connected to PORTB of a PIC microcontroller
and arranged such that they can show the faces of a dice when lit. Also a
push-button switch is connected to bit 7 of PORTB using a pull-up resis-
tor. When the switch is pressed the LEDs are lit randomly to show a dice
number between 1 and 6. Figure 5.35 shows the LEDs lit for a given dice
number.
o o o o o o
o • o • o • •••
o o o o o o
1 2 3
Figure 5.35 LED dice
o o o o • o
o
Hardware:
The circuit diagram of the project is shown in Figure 5.36. The 7 LEDs are
connected to bit to bit 6 of PORTB. Bit 7 of PORTB is connected to a
push-button switch which simulates the throwing of a dice when pressed.
A PIC16F627 model PIC microcontroller is used and the microcontroller
is operated from its 4 MHz internal clock. The LEDs are connected to
1
9V |o.33MFzz
Battery ,
78L05
^r
+5V
=^0.01uF
14
4.7K
Push to
Throw
Dice
Vdd
RB7
D
RBO
RB1
RB2
RB3
PIC RB4
16F627 RB5
RB6
Vss
6 330
7
10
— c
11
12
ZL
D1JI
%_
%
3f,
D7^|
Figure 5.36 Circuit diagram of Project 9
1 66 PIC BASIC projects
8 pins of PORTB using 330 fl current- limiting resistors. External reset
button is not used and power-on-reset is used with the MCLR disabled
during the programming of the device.
The project constructed on a breadboard is shown in Figure 5.37.
Figure 5.37 Construction of the project
Flow diagram:
The flow diagram of the project is shown in Figure 5.38. At the beginning
of the program the I/O direction is specified. When the switch is pressed
a random number generation is simulated between 1 and 6 and this num-
ber is then displayed on the LEDs which are constructed similar to the
face of a real dice.
Software:
PicBasic
The software for PicBasic language is given in Figure 5.39. At the begin-
ning of the program PORTB and TRISB addresses are defined. TRISB is
set to hexadecimal $80 so that bit 7 is configured as input port and bits
to 6 are configured as output ports. A number is generated between 1 and
6 by using a loop. Inside this loop if the switch is not pressed the dice
number is incremented by one between 1 and 6. When the number reaches
7 it is reset back to 1 so that the generated number is between 1 and 6. The
loop is executed so fast that the generated numbers can be considered to
be random. When the switch is pressed, the program jumps to label
NEWNO and here the current number (in variable DICE) is used in a
LOOKUP statement to determine the LEDs to be turned on. If the value
of DICE is 1, variable LEDS is loaded with $08. Similarly, if the value of
PicBasic and PicBasic Pro projects 167
C BEGIN J
v
Set port directions
i
'
DICE = 1
k
i
\
V
DICE = 1
N
^^ Switch ^\^
f
^\Pressed ^^^
t
Y
1
I Y
<^DICE = 7 ?J^>
Determine LEDs
to be turned on
^
i'
, N
Turn on LEDs
DICE = DICE + 1
^
f
Figure 5.38 Flow diagram of Project 9
DICE is 2, variable LEDS is loaded with $22 and so on. The required
LEDs are then turned on to display the number similar to the dots on a
dice. Table 5. 1 shows the relationship between the number to be displayed
and the LEDs to be turned on to display this number. For example, to dis-
play number 1 (i.e. only the middle LED is on), we have to turn on D4.
Similarly, to display number 4, we have to turn on Dl, D3, D5, and D7.
Table 5.1 Required number and LED to be turned on
Required number
LEDs to be turned on
1
D4
2
D2, D6
3
D2, D4, D6
4
D1,D3,D5,D7
5
D1,D3,D4,D5,D7
6
D1,D2,D3,D5,D6,D7
1 68 PIC BASIC projects
The relationship between the required number and the data to be sent to
PORTB to turn on the correct LEDs is given in Table 5.2. For example, to dis-
play dice number 2, we have to send hexadecimal $22 to PORTB. Similarly,
to display number 5, we have to send hexadecimal $5D to PORTB and so on.
Table 5.2 Required number and PORTB data
Required number
PORTB data (Hex)
1
$08
2
$22
3
$2A
4
$55
5
$5D
6
$77
LED DICE
7 LEDs are connected to PORTB of a PIC microcontroller and arranged as in the faces
of a dice. Also, a push-button switch is connected to bit 7 of PORTB.
When the switch is pressed the program generates a dice number
between 1 and 6 and turns on the appropriate LEDs to imitate the faces
of a real dice. The LEDs are turned on for 5 seconds and after this time
they are cleared and the program is ready to accept a new push-button
action.
The microcontroller is operated with internal 4MHz clock and internal
power-on-reset.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
LED15.BAS
Modifications
Figure 5.39 (Continued)
PicBasic and PicBasic Pro projects 169
' SYMBOLS
Symbol TRISB = $86
Symbol PORTB = $06
Symbol Switch = BO
Symbol LEDS = B1
Symbol DICE = B2
' TRISB address
' PORTB address
' Switch is a byte variable
' LEDs to be turned on
' Dice number (between 1 and 6)
' START OF MAIN PROGRAM
POKE TRISB, $80
' Wait until switch is pressed
' RB7 input, RB0-RB6 outputs
WAIT:
DICE = 1
NXT: PEEK PORTB, Switch
IF Bit7 = THEN NEWNO
DICE = DICE + 1
IF DICE = 7 THEN WAIT
GOTO NXT
NEWNO:
Check if switch is pressed
If pressed goto NEWNO
Increment dice number
between 1 and 6
repeat
' Find the LEDs to be turned on. DICE is between 1 and 6. LEDS is the data
' to be sent to PORTB to turn on the required LEDs
LOOKUP DICE, (0, $08, $22, $2A, $55, $5D, $77), LEDS
' Turn on the LEDs
POKE PORTB, LEDS
PAUSE 5000
POKE PORTB,
GOTO WAIT
END
Figure 5.39 PicBasic program of Project 9
Wait 5 seconds
Turn off all LEDs
Repeat
End of program
PicBasic Pro
The software for PicBasic Pro language is given in Figure 5.40. At the
beginning of the program TRISB is set to $80 to configure bit 7 of PORTB
as input and the other PORTB pins as outputs. The switch is then checked
1 70 PIC BASIC projects
inside a loop using an IF statement. If the switch is not pressed variable
DICE is incremented by one between 1 and 6. When the switch is pressed
the current value of DICE is taken and used in a LOOKUP statement to
obtain the data to be sent to PORTB so that the correct LEDs can be
turned on.
LED DICE
7 LEDs are connected to PORTB of a PIC microcontroller and arranged as in the faces
of a dice. Also, a push-button switch is connected to bit 7 of PORTB.
When the switch is pressed the program generates a dice number
between 1 and 6 and turns on the appropriate LEDs to imitate the faces
of a real dice. The LEDs are turned on for 5 seconds and after this time
they are cleared and the program is ready to accept a new push-button
action.
The microcontroller is operated with internal 4MHz clock and internal
power-on-reset.
Author: Dogan Ibrahim
Date: October, 2005
Compiler: PicBasic Pro
File: LED16.BAS
Modifications
DEFINITIONS
LEDS VAR BYTE
DICE VAR BYTE
' START OF MAIN PROGRAM
TRISB = $80
Figure 5.40 (Continued)
' RB7 input, RB0-RB6 outputs
PicBasic and PicBasic Pro projects 111
' Wait until switch is pressed
AGAIN:
DICE = 1
NXT: IF P0RTB.7 = THEN NEWNO
DICE = DICE + 1
IF DICE = 7 THEN AGAIN
GOTO NXT
NEWNO:
If pressed goto NEWNO
Increment dice number
between 1 and 6
repeat
' Find the LEDs to be turned on. DICE is between 1 and 6. LEDS is the data
' to be sent to PORTB to turn on the required LEDs
LOOKUP DICE, [0, $08, $22, $2A, $55, $5D, $77], LEDS
' Turn on the LEDs
PORTB = LEDS
PAUSE 5000
PORTB =
GOTO AGAIN
END
Figure 5.40 PicBasic Pro program of Project 9
' Turn on appropriate LEDs
' Wait 5 seconds
'Turn off all LEDs
' Repeat
' End of program
1 72 PIC BASIC projects
Project 1
Project title:
7-segment LED display counter
Project description: In this project, a 7-segment LED display is used as a counter. Numbers
from to 9 are displayed on the display continuously as 0123. ..890
12... with 1 s delay between each count.
Hardware:
7-Segment displays are frequently used in electronic circuits as indicators.
As shown in Figure 5.41, a 7-segment display basically consists of 7 LEDs
connected such that numbers from to 9 and some letters can be displayed.
Figure 5.42 shows the segment names of a typical 7-segment display.
Figure 5.41 Some 7-segment displays
Figure 5.42 Segment names of a 7-segment display
PicBasic and PicBasic Pro projects 173
Figure 5.43 shows how numbers from to 9 can be obtained by turning
on different segments of the display.
Figure 5.43 Obtaining numbers 0-9
7-segment displays are available in two different configurations: common
cathode and common anode. As shown in Figure 5.44, in common cath-
ode displays the cathodes of all the segment LEDs are tied together and
then this common point is connected to ground. A required segment is
then turned on by applying a logic 1 to the anode of this segment. Here,
the output pin of the microcontroller is in current sourcing mode.
Figure 5.44 Common cathode display
In a common-anode display, the anodes of all the segment LEDs are tied
together (see Figure 5.45) and then this common point is connected to V
supply voltage. A required segment is turned on by applying a logic to
the cathode of this segment. Here, the output pin of the microcontroller is
in current sinking mode.
1 74 PIC BASIC projects
v
+V
Figure 5.45 Common-anode display
In this project, a Kingbright SA52-11 model red common anode display is
used. This is a 13 mm height (0.52 inch) display with 10 pins. The pin
configuration is as shown in Table 5.3. The display also has a segment
LED for the decimal point.
Table 5.3 SA52-1 1 pin configuration
Pin Number
Segment
1
E
2
D
3
Common anode
4
C
5
Decimal point
6
B
7
A
8
Common anode
9
F
10
g
Figure 5.46 shows the circuit diagram of the project. A PIC16F627 model
PIC microcontroller is used and the microcontroller is operated from its
4 MHz internal clock and internal reset. The display is connected to PORTB
of the microcontroller using 330 fl current-limiting resistors in each
segment of the display.
The project constructed on a breadboard is shown in Figure 5.47.
The relationship between the displayed numbers and the data to be sent to
PORTB is shown in Table 5.4. The display is connected to the microcon-
troller using segments a to g. In this Table, x is a don'tcare entry, taken as
and is used to make the bit number 8. For example, to display number 2,
we have to send hexadecimal number $5B to PORTB. Similarly, to dis-
play number 8, we have to send hexadecimal number $7F to PORTB.
PicBasic and PicBasic Pro projects 175
1
+5V
9V ] 0.33 M F= =
Battery \
i
m
10
6
1
c
)P
5
Display Top View
Kingbright SA52-11
Figure 5.46 Circuit diagram of Project 10
Figure 5.47 Construction of the project
Flow diagram:
The flow diagram of the project is shown in Figure 5.48. At the beginning
of the program the I/O direction is specified by loading to TRISB, i.e.
all PORTB pins are configured as output pins. Then a loop is formed to
send numbers to 9 to the display. Inside the loop subroutine CONVERT
1 76 PIC BASIC projects
Table 5.4 Displayed number and data sent to PORTB
Number
x gf e d c b a
PORTB data
00111111
$3F
1
000001 10
$06
2
01011011
$5B
3
01001111
$4F
4
01100110
$66
5
1101101
$6D
6
0111110 1
$7D
7
1 1 1
$07
8
01111111
$7F
9
1101111
$6F
x is not used, taken as 0.
Y
BEGIN
Configure PORTB
as output
CNT =
CONVERT
Display number
CNT = CNT + 1
Delay 1 second
Subroutine CONVERT
BEGIN
1'
Determine bit
pattern to display a
digit on PORT B
^
r
RETURN
Figure 5.48 Flow diagram of Project 10
PicBasic and PicBasic Pro projects 111
is called to determine the actual data to be sent to PORTB in order to dis-
play the required number. This subroutine uses the LOOKUP statement to
determine the bit segments to be turned on for a required number. The
data to be sent to PORTB is inverted since we are using a common-anode
display (i.e. a segment is turned on by making the segment pin logic 0).
The process is repeated after a 1 s delay between each output.
Software: PicBasic
The software for PicBasic language is given in Figure 5.49. At the begin-
ning of the program PORTB andTRISB addresses are defined. Also, vari-
ables Cnt and Pattern are declared as byte variables. TRISB is cleared to
so that PORTB pins are configured as outputs. At the beginning of the
program variable Cnt is cleared to and subroutine CONVERT is called.
This subroutine receives Cnt as the input variable and returns the bit pat-
tern in variable Pattern. For example, if Cnt is 0, Pattern is assigned hexa-
decimal number $3F, if Cnt is 1, Pattern is assigned $06, etc. The bit
pattern is then inverted since we are using a common-anode type display
(a segment is turned on by clearing the segment pin). Variable Pattern is
inverted by performing a bit-wise Exclusive OR with hexadecimal num-
ber $FF (a bit is inverted when it is exclusive or'ed with 1). Variable Cnt
is then incremented and cleared to when it reaches 10 so that the num-
ber is between and 9. Otherwise, the program jumps to label NXT where
the next number is displayed. After displaying a number, the program
waits for 1 s and the process repeats forever.
7-SEGMENT DISPLAY COUNTER
In this project a common-anode type 7-segment display is connected
to PORTB of a PIC16F627 model microcontroller. The project displays
numbers to 9 on the display with 1 second delay between each output.
The microcontroller is operated with the internal 4MHz clock and also
the internal reset is used.
The connection between the microcontroller and the display is as
follows:
RBO segment a
RB 1 segment b
Figure 5.49 (Continued)
178 PIC BASIC projects
RB2
RB3
RB4
RB5
RB6
segment c
segment d
segment e
segment f
segment g
The decimal point of the display is not used.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
LED 1 7. B AS
Modifications
SYMBOLS
Symbol TRISB = $86
Symbol PORTB = $06
Symbol Cnt = BO
Symbol Pattern = B 1
' TRISB address
' PORTB address
' Cnt is a byte variable
' Pattern is a byte variable
' START OF MAIN PROGRAM
POKE TRISB,
' PORTB is output
LOOP:
Cnt =
NXT:
GOSUB CONVERT
POKE PORTB, Pattern
Cnt = Cnt + 1
PAUSE 1000
IF CNT = 10 THEN LOOP
GOTO NXT
Figure 5.49 (Continued)
' Initialise CNT to
' Find the bit pattern to send to PORTB
' Send Pattern to PORTB
' Increment count
' Wait 1 second
PicBasic and PicBasic Pro projects 179
CONVERT:
Find the bit pattern to be sent to PORTB in order to turn on the correct segments
to display the required number. Cnt contains a number between and 9 and
on return from LOOKUP statement, Pattern contains the bit pattern to send to
PORTB to display the required number in Cnt. Because we are using a
common-anode display, a segment is turned on when it is logic and thus the
bit pattern is inverted before sending to PORTB.
LOOKUP Cnt, ($3F, $06, $5B, $4F, $66, $6D, $7D, $07, $7F, $6F), Pattern
Pattern = Pattern A $FF ' Invert bits of variable Pattern
RETURN
END ' End of program
Figure 5.49 PicBasic program of Project 10
PicBasic Pro
The software for PicBasic Pro language is given in Figure 5.50. At the
beginning of the program TRISB is set to to configure PORTB pins as
outputs. Variable Cnt is then cleared to and subroutine CONVERT is
called to find the bit pattern to be displayed. Statement LOOKUP
receives Cnt as the input variable and returns the required bit pattern in
variable Pattern. The bit pattern is then inverted and sent to PORTB to
turn on the required display segments. Variable Cnt is incremented and
cleared to when it reaches 10 so that the number is between and 9. The
value of Cnt is sent to the display every second.
7-SEGMENT DISPLAY COUNTER
In this project a common-anode type 7-segment display is connected
to PORTB of a PIC16F627 model microcontroller. The project displays
numbers to 9 on the display with 1 second delay between each output.
The microcontroller is operated with the internal 4MHz clock and also
the internal reset is used.
Figure 5.50 (Continued)
1 80 PIC BASIC projects
The connection between the microcontroller and the display is as
follows:
RBO
segment a
RBI
segment b
RB2
segment c
RB3
segment d
RB4
segment e
RB5
segment f
RB6
segment g
The decimal point of the display is not used.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED18.BAS
Modifications
DEFINITIONS
Cnt VAR Byte
Pattern VAR Byte
' START OF MAIN PROGRAM
TRISB =
LOOP:
Cnt =
NXT: GOSUB CONVERT
PORTB = Pattern
Cnt = Cnt + 1
PAUSE 1000
IF CNT = 10 THEN LOOP
GOTO NXT
Figure 5.50 (Continued)
' PORTB is output
' Initialise CNT to
' Find the bit pattern to send to PORTB
' Send Pattern to PORTB
' Increment count
' Wait 1 second
PicBasic and PicBasic Pro projects 181
CONVERT:
Find the bit pattern to be sent to PORTB in order to turn on the correct segments
to display the required number. Cnt contains a number between and 9 and
on return from LOOKUP statement, Pattern contains the bit pattern to send to
PORTB to display the required number in Cnt. Because we are using a
common-anode display, a segment is turned on when it is logic and thus the
bit pattern is inverted before sending to PORTB.
LOOKUP Cnt, [$3F, $06, $5B, $4F, $66, $6D, $7D, $07, $7F, $6F], Pattern
Pattern = Pattern A $FF ' Invert bits of variable Pattern
RETURN
END ' End of program
Figure 5.50 PicBasic Pro program of Project 10
1 82 PIC BASIC projects
Project 1 1
Project title:
Project description:
Hardware:
7-segment LED dice
In this project, a 7-segment LED display is used as a dice. Normally the
display shows a "0" to indicate that it is waiting for a key press. When the
external push-button switch is pressed, a dice number is displayed
between 1 and 6 for 3 s. After this time the display clears back to "0" to
indicate that it is waiting again for a key press.
The circuit diagram of this project is similar to Figure 5.46. A common-
anode type 7-segment display is connected as in Figure 5.46, and in add-
ition a push-button switch is connected to bit 7 of PORTB. As shown in
Figure 5.51, the switch is normally held at logic 1 using a pull-up resistor.
1
_ 9 H V |0.33UF = =
Battery ,
i
78L05
t:
+5V
dp 0.01 [if
14
Push to
Start
10
6
1
[
)P
O
5
10K
rn ! 13
-°1
Display Top View
Figure 5.51 Circuit diagram of Project 1 1
Vdd
RB7
RB0
RB1
RB2
RB3
PIC R B4
16F627 RB5
RB6
Vss
6 330
-nz
7
8
-nz
9
10
— c
11
12
X
7
6
1_^
b
c
d
e
f
1 Ho
KingbrightSA52-11
Flow diagram:
The project constructed on a breadboard is shown in Figure 5.52.
The flow diagram of the project is shown in Figure 5.53. At the beginning
of the program the I/O direction is specified by loading hexadecimal $80
to TRISB, i.e. PORTB pins to 6 are outputs and bit 7 is input. The pro-
gram then waits for the switch to be pressed. When the switch is pressed,
a random number is generated between 1 and 65,535 using the PicBasic
PicBasic and PicBasic Pro projects 183
Figure 5.52 Construction of the project
BEGIN
'
r
Configure RB0-RB6
as output and RB7
as input
i
r
Generate a new
random number
N
Y
/^ Switch ^^
^\ pressed ?^^
Y J
<^Number = 7 ?^>
N^\/^^
CONVERT
i
-
Display number
y
'
Delay 3 seconds
i
r
Figure 5.53 Flow diagram of Project 1 1
1 84 PIC BASIC projects
RANDOM statement. The generated number is bit-wise ANDed with 7 so
that it is between 1 and 7. If the number is 7, a new random number is
obtained such that the number is between 1 and 6. Subroutine CONVERT
is called to find the bit pattern to be sent to PORTB to turn on the required
segments. As in Project 10, this subroutine uses the LOOKUP statement
to determine the bit segments to be turned on for a required number. The
data to be sent to PORTB is inverted since we are using a common-anode
display (i.e. a segment is turned on by making the segment pin logic 0).
The dice number is displayed for 3 s. After this time the display is cleared
to and the program is ready for a new key press.
Software: PicBasic
The software for PicBasic language is given in Figure 5.54. At the begin-
ning of the program PORTB and TRISB addresses are defined. TRISB is
set to $80 so that bits to 6 of PORTB are configured as outputs and bit
7 is configured as input. The program then waits for the push-button to be
pressed. When the key is pressed a new random number is generated
between 1 and 65,535 using the PicBasic Pro RANDOM statement. The
generated number is bit-wise ANDed with 7 so that it is between 1 and 7.
If the number is 7, a new random number is obtained such that the num-
ber is between 1 and 6. Subroutine CONVERT uses statement LOOKUP
to determine the bit pattern to be sent to PORTB. The data to be sent to
PORTB is inverted since we are using a common-anode display. The dice
number is displayed for 3 s. After this time the display is cleared to and
the program is ready for a new key press, or'ed with 1.
7-SEGMENT DICE
In this project a common-anode type 7-segment display is connected
to PORTB of a PIC16F627 model microcontroller. Additionally, a
push-button switch is connected to bit 7 of PORTB. When the button
is pressed, the project displays a number between 1 and 6 just like a
dice. The RANDOM statement is used to generate a random number.
The microcontroller is operated with the internal 4MHz clock and also
the internal reset is used.
Figure 5.54 (Continued)
PicBasic and PicBasic Pro projects 1 85
The connection between the microcontrolelr and the display is as
follows:
RBO
segment a
RBI
segment b
RB2
segment c
RB3
segment d
RB4
segment e
RB5
segment f
RB6
segment g
The decimal point of the display is not used.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
LED19.BAS
Modifications
' TRISB address
' PORTB address
' Switch is a word variable
' Pattern is a byte variable
' Dice is a word variable
SYMBOLS
Symbol TRISB = $86
Symbol PORTB = $06
Symbol Switch = BO
Symbol Pattern = Bl
Symbol Dice = Wl
' START OF MAIN PROGRAM
POKE TRISB, $80
LOOP:
DICE =
GOSUB CONVERT
POKE PORTB, Pattern
WT: RANDOM Dice
PEEK PORTB, Switch
IF Bit7 = 1 THEN WT
Figure 5.54 (Continued)
' Bits 0-6 are outputs, bit 7 is input
' Display at the beginning
' Display to show that we are ready
' Generate a random number between and 65535
' Wait until switch is pressed
1 86 PIC BASIC projects
BR: Dice = Dice & 7
IF Dice <> 7 THEN NXT
RANDOM Dice
GOTO BR
NXT: GOSUB CONVERT
POKE PORTB, Pattern
PAUSE 3000
GOTO LOOP
' Number between and 7
' If the number is or 7, get a new number
' Find the bit pattern to send to PORTB
' Send Pattern to PORTB
' Wait 3 seconds
CONVERT:
Find the bit pattern to be sent to PORTB in order to turn on the correct segments
to display the required number. Dice contains a number between 1 and 6 and
on return from LOOKUP statement, Pattern contains the bit pattern to send to
PORTB to display the required number in Dice. Because we are using a
common-anode display, a segment is turned on when it is logic and thus the
bit pattern is inverted before sending to PORTB.
LOOKUP Dice, ($3F, $06, $5B, $4F, $66, $6D, $7D, $07, $7F, $6F), Pattern
Pattern = Pattern A $FF ' Invert bits of variable Pattern
RETURN
END
Figure 5.54 PicBasic program of Project 10
' End of program
PicBasic Pro
The software for PicBasic Pro language is shown in Figure 5.55. The pro-
gram is very similar to the PicBasic program given in Figure 5.54 with the
exception that the registers are addressed directly.
7-SEGMENT DICE
In this project a common-anode type 7-segment display is connected
to PORTB of a PIC16F627 model microcontroller. Additionally, a
push-button switch is connected to bit 7 of PORTB. When the button
is pressed, the project displays a number between 1 and 6 just like a
dice. The RANDOM statement is used to generate a random number.
Figure 5.55 (Continued)
PicBasic and PicBasic Pro projects 1 87
The microcontroller is operated with the internal 4MHz clock and also
the internal reset is used.
The connection between the microcontroller and the display is as
follows:
RBO segment a
RB 1 segment b
RB2 segment c
RB3 segment d
RB4 segment e
RB5 segment f
RB6 segment g
The decimal point of the display is not used.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED20.BAS
Modifications
DEFINITIONS
Pattern VAR Byte
Dice VAR WORD
' START OF MAIN PROGRAM
TRISB = $80 ' Bits 0-6 are outputs, bit 7 is input
LOOP: ' Display at the beginning
DICE =
GOSUB CONVERT
PORTB = Pattern ' Display to show that we are ready
WT: RANDOM Dice ' Generate a random number between and 65535
IF PORTB. 7 = 1 THEN WT ' Wait until switch is pressed
Figure 5.55 (Continued)
188 PIC BASIC projects
BR:
NXT:
Dice = Dice & 7
IF Dice <> 7 THEN NXT
RANDOM Dice
GOTO BR
GOSUB CONVERT
PORTB = Pattern
PAUSE 3000
GOTO LOOP
' Number between and 7
' If the number is or 7, get a new number
' Find the bit pattern to send to PORTB
' Send Pattern to PORTB
' Wait 3 seconds
CONVERT:
Find the bit pattern to be sent to PORTB in order to turn on the correct segments
to display the required number. Dice contains a number between 1 and 6 and
on return from LOOKUP statement, Pattern contains the bit pattern to send to
PORTB to display the required number in Dice. Because we are using a
common-anode display, a segment is turned on when it is logic and thus the
bit pattern is inverted before sending to PORTB.
LOOKUP Dice, [$3F, $06, $5B, $4F, $66, $6D, $7D, $07, $7F, $6F], Pattern
Pattern = Pattern A $FF ' Invert bits of variable Pattern
RETURN
END ' End of program
Figure 5.55 PicBasic Pro program of Project 1 1
PicBasic and PicBasic Pro projects 1 89
Project 12
Project title:
Dual 7-segment LED display
Project description: In this project two 7-segment displays are used. Then, a number (in this
case 25) is shown on the displays.
Hardware:
When more than one 7-segment display is used the displays are configured
and controlled as multiplexed units. Here, as shown in Figure 5.56, the seg-
ments of the displays are connected in parallel and their common points
are driven separately, each one for a brief period of time. For example, to
display number 25, we have to send 2 to the first digit and enable its com-
mon point. After a few milliseconds, number 5 is sent to the second digit
and the common point of the second digit is enabled. When this process is
repeated continuously the user sees as if both displays are on continuously.
Digit 1 Enable
Digit 2 Enable
Figure 5.56 Connecting two 7-segment displays in parallel
Some display manufacturers provide multiplexed multi-digit displays in
single packages. One such device is the D56 series displays. These are
dual red or green colour common-anode or common-cathode displays
where the segments of both digits are paralleled and each digit has a sep-
arate common control pin. The display used in this project is the D56E05
which is a red colour common-anode two digit display which has the pin
configuration as in Table 5.5. This display can be controlled as follows:
• Send the segment data for digit 1 to segments a to g
• Enable digit 1 by connecting digit 1 enable pin to +V supply
• Wait for a few milliseconds
• Send the segment data for digit 2 to segments a to g
• Enable digit 2 by connecting digit 2 enable pin to +V supply
• Wait for a few milliseconds
• Repeat this process continuously
1 90 PIC BASIC projects
Table 5.5 Pin configi
uration of D56E05 dual display
Pin number
Segment
1
E
2
D
3
C
4
Digit 1 enable
5
G
6
B
7
A
8
F
9
Digit 2 enable
10
Decimal point
The circuit diagram of the project is shown in Figure 5.57. Display seg-
ments are connected to PORTB. Digit 1 and Digit 2 inputs are connected
to port pins RAO and RA1, respectively, using NPN transistors (e.g.
2N2222 or BC108 or any other type). A display digit is enabled by mak-
ing the base of the corresponding digit transistor logic 1 . When the tran-
sistor is turned on, current flows through the collector-emitter junction,
thus enabling the display.
9V
Battery ,
BC108
D56E05 Common Anode
Figure 5.57 Circuit diagram of Project 12
PicBasic and PicBasic Pro projects 191
The project constructed on a breadboard is shown in Figure 5.58.
Figure 5.58 Construction of the project
Flow diagram:
The flow diagram of the project is shown in Figure 5.59. At the beginning
of the program PORTA and PORTB pins are configured as outputs.
Variable Cnt stores the number to be displayed (loaded with number 25 in
this example). First, 10s digit of the display is obtained by dividing Cnt by
10. Subroutine CONVERT is then called to obtain the segments to be
turned on. This bit pattern is sent to PORTB and then digit 1 is enabled by
setting bit of PORTA to logic 1. As a result of this the 10 s digit is dis-
played. After 1 ms delay the 1 s digit is obtained and the corresponding
segment bit pattern is sent to PORTB and then digit 2 is enabled by set-
ting bit 1 of PORTA to logic 1. As a result of this the Is digit is displayed.
The above process is repeated forever.
Software:
PicBasic
The software for PicBasic language is given in Figure 5.60. At the begin-
ning of the program TRISA and TRISB registers are cleared so that
PORTA and PORTB pins are configured as outputs. CMCON register is
then set to 7 so that RAO and RA1 ports are configured as digital I/O. Cnt,
Temp, Digit, and Pattern are declared as byte variables. Variable Cnt is set
to number 25 and this is the value we wish to display. Cnt is divided by 10
to obtain the 10 s digit of Cnt and this number is stored in variable Digit.
1 92 PIC BASIC projects
BEGIN
)
ir
Configure PORTA and
PORTB as outputs
i
Cnt = 25
f
i
Get 10s digit
w
CONVERT
ir
Send to PORTB
i
r
Enable Digit 1
i
f
2ms delay
^
f
Get 10s digit
i
r
CONVERT
i
*
Send to PORTB
i
f
Enable Digit 2
i
f
2ms delay
i
'
Figure 5.59 Flow diagram of Project 12
PicBasic and PicBasic Pro projects 193
DUAL 7-SEGMENT LED DISPLAY
In this project two 7-segment LED displays are connected to PORTB
of a PIC16F627 type microcontroller. The program displays the number
in variable Cnt on the displays (Cnt is made equal to 25 in this example).
The conenction between the LEDs and the microcontroller are as follows:
RBO
segment a
RBI
segment b
RB2
segment c
RB3
segment d
RB4
segment e
RB5
segment f
RB6
segment g
RAO
digit 1 enable
RA1
digit 2 enable
Left digit is Digit 1 and right digit is Digit 2.
The microcontroller operates with a 4MHz internal clock and internal
power-on reset.
Author: Dogan Ibrahim
Date: October, 2005
Compiler: PicBasic
File: LED21.BAS
Modifications
SYMBOLS
Symbol TRISA = $85 ' TRISA address
Symbol TRISB = $86 ' TRISB address
Symbol PORTA = $05 ' PORTA address
Figure 5.60 (Continued)
1 94 PIC BASIC projects
Symbol PORTB = $06
Symbol CMCON = $1F
Symbol Cnt = BO
Symbol Temp = B 1
Symbol Digit = B2
Symbol Pattern = B3
' PORTB address
' CMCON address
' Cnt is a byte variable
' Temp is a byte variable
' Digit is a byte variable
' Pattern is a byte variable
' START OF MAIN PROGRAM
POKE CMCON, 7
POKE TRIS A,
POKE TRISB,
Cnt = 25
NXT:
Digit = Cnt/ 10
GOSUB CONVERT
POKE PORTB, Pattern
POKE PORTA, 1
PAUSE 2
Temp = Digit * 10
Digit = Cnt - Temp
GOSUB CONVERT
POKE PORTB, Pattern
POKE PORTA, 2
PAUSE 2
GOTO NXT
CONVERT:
' RA0-RA3 are digital I/O
' Set PORTA as output
' Set all PORTB pins as outputs
' Number to display in Cnt
' Get 10s digit
' Get segments to turn on
' Display 10s digit
' Enable Digit 1
' Wait 2ms
' Get Is digit
' Get segments to turn on
' Display Is digit
' Enable Digit 2
' Wait 2ms
' Continue displaying
Find the bit pattern to be sent to PORTB in order to turn on the correct segments
to display the required number. Digit contains a number between and 9 and
on return from LOOKUP statement, Pattern contains the bit pattern to send to
PORTB to display the required number in Digit. Because we are using a
common-anode display, a segment is turned on when it is logic and thus the
bit pattern is inverted before sending to PORTB.
LOOKUP Digit, ($3F, $06, $5B, $4F, $66, $6D, $7D, $07, $7F, $6F), Pattern
Pattern = Pattern A $FF ' Invert bits of variable Pattern
RETURN
END
Figure 5.60 PicBasic program of Project 12
' End of program
PicBasic and PicBasic Pro projects 195
Subroutine CONVERT is called to obtain the segments to be turned on.
CONVERT receives Digit as the input variable and returns variable
Pattern as the output. Pattern is then sent to PORTB and bit of PORTA
is set to logic 1 to enable digit 1 . After a delay of 1 ms, digit 2 is obtained
in variable Digit. Subroutine CONVERT is called again to obtain the seg-
ments to be turned on. The program then sends the segment pattern to
PORTB and sets bit 1 of PORTA to enable digit 2. Program then jumps to
label NXT and the process is repeated forever.
PicBasic Pro
The software for PicBasic Pro language is shown in Figure 5.61. At the
beginning of the program TRISA and TRISB registers are cleared so that
PORTA and PORTB pins are configured as outputs. CMCON register is
then set to 7 so that RAO and RA1 ports are configured as digital I/O. Cnt,
Temp, Digit, and Pattern are declared as byte variables. Variable Cnt is set
to number 25 and this is the value we wish to display. PicBasic Pro state-
ment "DIG 1" is used to obtain the first digit of Cnt and subroutine CON-
VERT is called to obtain the segments to be turned on. CONVERT receives
Digit as the input variable and returns variable Pattern as the output. Pattern
is then sent to PORTB and bit of PORTA is set to logic 1 to enable digit 1 .
After a delay of 1 ms, digit 2 is obtained by using the PicBasic Pro state-
ment "DIG 0" and subroutine CONVERT is called again to obtain the seg-
ments to be turned on for digit 2. The program then sends the segment
pattern to PORTB and sets bit 1 of PORTA to enable digit 2. Program then
jumps to label NXT and the process is repeated forever.
DUAL 7-SEGMENT LED DISPLAY
In this project two 7-segment LED displays are connected to PORTB
of a PIC16F627 type microcontroller. The program displays the number
in variable Cnt on the displays (Cnt is made equal to 25 in this example).
The conenction between the LEDs and the microcontroller are as follows:
RBO segment a
RB 1 segment b
RB2 segment c
Figure 5.61 (Continued)
1 96 PIC BASIC projects
RB3
segment d
RB4
segment e
RB5
segment f
RB6
segment g
RAO
digit 1 enable
RA1
digit 2 enable
Left digit is Digit 1 and right digit is Digit 2.
The microcontroller operates with a 4MHz internal clock and internal
power-on reset.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED22.BAS
Modifications
' DEFINITIONS
Cnt
VAR
Byte
' Cnt is a byte variable
Digit
VAR
Byte
' Digit is a byte variable
Pattern
VAR
Byte
' Pattern is a byte variable
Digitl
VAR
PORTA.O
' Digit 1 enable bit
Digit2
VAR
PORTA. 1
' Digit 2 enable bit
' START OF MAIN PROGRAM
CMCON = 7
TRISA =
TRISB =
Cnt = 25
NXT:
Digitl =
Digit2 =
Figure 5.61 (Continued)
' RA0-RA3 are digital I/O
' Set PORTA as output
' Set all PORTB pins as outputs
' Number to display in Cnt
' Disable digit 1
' Disable digit 2
PicBasic and PicBasic Pro projects 197
Digit = Cnt DIG 1
GOSUB CONVERT
PORTB = Pattern
Digit 1 = 1
PAUSE 2
Digit = Cnt DIG
GOSUB CONVERT
PORTB = Pattern
Digit2 = 1
PAUSE 2
GOTO NXT
' Get 10s digit
' Get segments to turn on
' Display 10s digit
' Enable Digit 1
' Wait 2ms
' Get Is digit
' Get segments to turn on
' Display Is digit
' Enable Digit 2
' Wait 2ms
' Continue displaying
CONVERT:
Find the bit pattern to be sent to PORTB in order to turn on the correct segments
to display the required number. Digit contains a number between and 9 and
on return from LOOKUP statement, Pattern contains the bit pattern to send to
PORTB to display the required number in Digit. Because we are using a
common-anode display, a segment is turned on when it is logic and thus the
bit pattern is inverted before sending to PORTB.
LOOKUP Digit, [$3F, $06, $5B, $4F, $66, $6D, $7D, $07, $7F, $6F], Pattern
Pattern = Pattern A $FF ' Invert bits of variable Pattern
RETURN
END
Figure 5.61 PicBasic Pro program of Project 12
' End of program
1 98 PIC BASIC projects
Project 13
Project title:
Project description:
Hardware:
Flow diagram:
Dual 7-segment LED display counter
In this project two 7-segment displays are used as in Project 12. The project
works like a counter where numbers 00 to 99 are shown on the display with
a few seconds delay between each output. The count is repeated after 99.
The circuit diagram of the project is as in Project 12 (Figure 5.57). That
is, display segments are connected to PORTB, and display digits are con-
trolled from bit and bit 1 of PORT A.
One of the problems in this project is that the display digits require to be
updated continuously so that we can see the numbers displayed on each
digit. But at the same time we have to increment the count and wait a few
seconds before sending a new value to the display. This requires a multi-
tasking approach where the display can be updated independent of the
counting function. One solution to this problem is to update the display
inside a timer interrupt routine which can be done independent of other
functions of the program.
The timer interrupt TMRO can be configured to interrupt at required inter-
vals. When the timer interrupt is enabled and a 4-MHz clock is used, TMRO
interrupt occurs at the time given by T, where T is in microseconds and
T = Pre-scaler value X (256 -TMRO value)
In this project we shall set the TMRO to generate interrupts at every 10 ms
and this will be our display update time. If we choose a pre-scaler value
of 256, the value to be loaded into the TMRO register is found to be
TMRO = 256 - 10,000/256
which is about 217.
The flow diagram of the project is shown in Figure 5.62. At the beginning
of the program PORTA and PORTB pins are configured as outputs, and
timer interrupt TMRO is enabled. The program consists of two sections:
the Main Program and the Interrupt Service Routine (ISR).
Inside the main program variable Cnt is initialised to and the program
increments Cnt by 1 after every second. When Cnt reaches 99, it is cleared
again to 0. Subroutine CONVERT is then called to find the segments to
be turned on to display a required number.
The display is updated inside the ISR every time a timer interrupt occurs,
independent of the main program. Timer register TMRO is re-loaded with
217 as soon as an interrupt is generated.
PicBasic and PicBasic Pro projects 199
C BEGIN J
i '
Configure PORTA and
PORTB as outputs
^ '
Configure INTCON
and OPTION_REG
^ '
Define interrupt
service routine
'
i
Cnt =
i '
Determine segments to turn
on to display the number
i
'
Delay 1 second
i
'
Cnt = Cnt + 1
Y
<^ Cnt
N
'
> yy >
ISR
( BEGIN J
i
r
Re-load TMRO
i
'
Enable digit 1
^
'
Enable digit 2
'
'
RETURN
Figure 5.62 Flow diagram of Project 13
200 PIC BASIC projects
Software: PicBasic
PicBasic language does not support the use of interrupts from high-level
and thus only the PicBasic Pro program is given for this project.
PicBasic Pro
Figure 5.63 shows the program listing. At the beginning of the program
PORTA and PORTB pins are configured as outputs, and timer interrupt
TMRO is enabled. The program consists of two sections: the Main
Program, and the ISR.
Inside the main program variable Cut is initialised to and the program
increments Cnt by 1 after every second. When Cnt reaches 99, it is cleared
again to 0. Interrupt control register INTCON is configured so that timer
TMRO interrupts are enabled. Also, the OPTION_REG register is config-
ured so that the pre-scaler value is 256. PicBasic Pro statements "DIG 1"
and "DIG 0" are used to extract the 10s and the Is digit of a number.
Subroutine CONVERT is then called to find the segments to be turned on
to display a required number. Variables First and Second store the seg-
ments to be turned on for digit 1 and digit 2, respectively.
The display is updated inside the ISR every time a timer interrupt occurs,
independent of the main program. Timer register TMRO is re-loaded with
217 as soon as an interrupt is generated.
Note that in PicBasic Pro language, interrupts are only recognised
between the statements. This is why the 1 s delay is made up of a FOR
loop with a loop count of 1000 and a delay of 1 ms inside the loop. This
way, interrupts can be recognised in between the 1 ms delays.
DUAL 7-SEGMENT LED COUNTER
In this project two 7-segment LED displays are connected to PORTB
of a PIC16F627 type microcontroller. The program works as a counter
where numbers 00 to 99 are displayed with a few seconds delay between
each output.
The program consists of two sections: the main program and the interrupt
service routine (ISR). The counter increments inside the main program and
the TMRO interrupt routine is used to update the displays.
Figure 5.63 (Continued)
PicBasic and PicBasic Pro projects 201
The conenction between the LEDs and the microcontroller are as follows:
RBO
segment a
RBI
segment b
RB2
segment c
RB3
segment d
RB4
segment e
RB5
segment f
RB6
segment g
RAO
digit 1 enable
RA1
digit 2 enable
Left digit is Digit 1 and right digit is Digit 2.
The microcontroller operates with a 4MHz internal clock and internal
power-on reset.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED23.BAS
Modifications
' DEFINITIONS
Cnt VAR
Byte
Digit VAR
Byte
Pattern VAR
Byte
Digitl VAR
PORTA.O
Digit2 VAR
PORTA. 1
First VAR
Byte
Second VAR
Byte
i VAR
Word
' Cnt is a byte variable
' Digit is a byte variable
' Pattern is a byte variable
' Digit 1 enable bit
' Digit 2 enable bit
' First is a byte variable
' Second is a byte variable
' i is a word variable
Figure 5.63 (Continued)
202 PIC BASIC projects
' START OF MAIN PROGRAM
CMCON = 7
TRISA =
TRISB =
' Enable TMRO timer interrupts
INTCON = %00 100000
OPTION_REG = %000001 1 1
TMRO = 217
ON INTERRUPT GOTO ISR
INTCON = % 10 100000
' RA0-RA3 are digital I/O
' Set PORTA as output
' Set all PORTB pins as outputs
' Enable TMRO interrupts
' Initialise the prescale
' Load TMRO register
' Enable Interrupts
LOOP:
Cnt =
NXT:
Digit = Cnt DIG 1
GOSUB CONVERT
First = Pattern
Digit = Cnt DIG
GOSUB CONVERT
Second = Pattern
' Initialise Cnt to
' Get 10s digit
' Get segments to turn on
' Display 10s digit
' Get Is digit
' Get segments to turn on
' Display Is digit
FORi= 1 to 1000
Pause 1
NEXTi
' Wait 1 second
Cnt = Cnt + 1
IF Cnt > 99 THEN LOOP
GOTO NXT
' Increment Cnt
' If Cnt > 99 then goto LOOP
' Continue
' This is the Interrupt Service Routine (ISR). The program jumps to this
' routine whenever a timer interrupt is generated.
DISABLE
ISR:
TMRO = 216
PORTB = First
Digit2 =
Digit 1 = 1
PAUSE 5
Figure 5.63 (Continued)
' Disable further interrupts
PicBasic and PicBasic Pro projects 203
Digit 1 =
PORTB = Second
Digit2 = 1
PAUSE 1
INTCON.2 = ' Re-enable TMRO interrupts
RESUME ' Return to main program
ENABLE ' Enable interrupts
CONVERT:
Find the bit pattern to be sent to PORTB in order to turn on the correct segments
to display the required number. Digit contains a number between and 9 and
on return from LOOKUP statement, Pattern contains the bit pattern to send to
PORTB to display the required number in Digit. Because we are using a
common-anode display, a segment is turned on when it is logic and thus the
bit pattern is inverted before sending to PORTB.
LOOKUP Digit, [$3F, $06, $5B, $4F, $66, $6D, $7D, $07, $7F, $6F], Pattern
Pattern = Pattern A $FF ' Invert bits of variable Pattern
RETURN
END ' End of program
Figure 5.63 PicBasic Pro program of Project 13
204 PIC BASIC projects
Project 14
Project title:
Project description:
Hardware:
Dual 7-segment LED event counter
In this project two 7-segment displays are used as in Project 13. A push-
button switch is connected to bit 7 of PORTB. The project counts and dis-
plays the number of times the switch is pressed. This project can be used
to count events in many other applications, such as counting the number of
products passing on a conveyor belt, number of people entering a building,
number of cars entering a car park, and so on.
The circuit diagram of the project is similar to Figure 5.57, but here, as
shown in Figure 5.64, a push-button switch is connected to bit 7 of PORTB.
A pull-up resistor is used so that the switch is normally at logic 1 and goes
to logic when it is pressed.
The timer TMRO interrupt as in Project 13 is used to display the count on
the dual 7-segment display.
1
J} 1 | 0.33 uF = =
Battery \ ^
78L05
t:
+5V
=b0.0lMF
10K
Push to
Count H
14
17
13
O-
Vdd
RAO
RA1
RB7
RBO
RB1
RB2
RB3
PIC RB4
16F627 RB5
RB6
Vss
6 330
7
8
9
10
11
12
X
Figure 5.64 Circuit diagram of Project 14
1K
7
BC108
"L_3
7
6 b
c
d
e
f
1K
J
\
BC108
D56E05 Common Anode
Flow diagram:
The flow diagram of the project is shown in Figure 5.65. At the beginning
of the program PORTA and PORTB pins are configured as outputs, and
timer interrupt TMRO is enabled. The program consists of two sections:
the Main Program, and the ISR.
PicBasic and PicBasic Pro projects 205
BEGIN
Configure PORT A and
PORT B as outputs
Configure INTCON
and OPTION REG
Define interrupt
service routine
Cnt =
-><-
N
Cnt = Cnt + 1
ISR
BEGIN
Re-load TMRO
Determine
segments to turn on
Display Cnt
RETURN
Figure 5.65 Flow diagram of Project 14
206 PIC BASIC projects
Inside the main program variable Cnt is initially cleared to and the switch
is tested continuously and the program waits until the switch is pressed.
Every time the switch is pressed variable Cnt is incremented by 1 . The value
of Cnt is displayed inside the ISR every 10 ms. In a practical application the
program should check to make sure that Cnt does not become greater than
99 and give an alarm or some other warning before this happens.
The display is updated inside the ISR every time a timer interrupt occurs,
independent of the main program. Timer register TMRO is re-loaded with
217 as soon as an interrupt is generated. As in Project 13, timer interrupts
are generated at 10 ms intervals.
Software: PicBasic
PicBasic language does not support the use of interrupts from high-level
and thus only the PicBasic Pro program is given for this project.
PicBasic Pro
Figure 5.66 shows the program listing. At the beginning of the program
PORTA and PORTB pins are configured as outputs, and timer interrupt
TMRO is enabled. The program consists of two sections: the Main Program
and the ISR.
Inside the main program INTCON register is configured so that timer TMRO
interrupts are enabled. Also, the OPTION_REG register is configured so
that the pre-scaler value is 256. Variable Cnt is initialised to and the pro-
gram increments Cnt by 1 every time the switch is pressed (or whenever an
external event occurs). In this program PicBasic Pro statement BUTTON is
used to find out when the switch is pressed. The statement is configured to
eliminate switch-bouncing problems. Switch-contact bouncing happens
when a switch is pressed or released. Switch contacts oscillate and generate
noise which may cause the microcontroller to read multiple on/off readings
or wrong switch state when the switch is pressed or released.
The display is updated inside the ISR. PicBasic Pro statements "DIG 1" and
"DIG 0" are used to extract the 10 s and the Is digits of variable Cnt. PicBasic
Pro statement LOOKUP is used to find the segments to be turned on to dis-
play each digit of Cnt. The bits are inverted before they are sent to the display.
This is done because a display segment is turned on when a logic is applied
(common-anode display) to the segment. The inversion is done by bit-wise
exclusive-or'ing the bit data with hexadecimal number $FF (a bit exclusive-
or'ed with 1 is inverted). At the beginning of the ISR, timer register TMRO is
re- loaded with 217 so that the next interrupt is generated after 10ms.
PicBasic and PicBasic Pro projects 207
DUAL 7-SEGMENT EVENT COUNTER
In this project two 7-segment LED displays are connected to PORTB
of a PIC16F627 type microcontroller. Also, a push-button switch is
connected to bit 7 of PORTB. The program counts and displays how
many times the switch is pressed. Although a simple switch is used
in this example, the project can be used to count events such as the
number of objects passing on a conveyor belt, number of cars entering
a car park etc.
In this project the switch is debounced to eliminate the contact problems
using the PicBasic Pro BUTTON statement.
The program consists of two sections: the main program and the interrupt
service routine (ISR). The counter increments inside the main program and
the TMRO interrupt routine is used to update the displays.
The conenction between the LEDs and the microcontroller are as follows:
RBO
segment a
RBI
segment b
RB2
segment c
RB3
segment d
RB4
segment e
RB5
segment f
RB6
segment g
RAO
digit 1 enable
RA1
digit 2 enable
RB7 push-button switch
Left digit is Digit 1 and right digit is Digit 2.
The microcontroller operates with a 4MHz internal clock and internal
power-on reset.
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED24.BAS
Figure 5.66 (Continued)
208 PIC BASIC projects
Modifications
' DEFINITIONS
Cnt VAR
Byte
Digit VAR
Byte
Pattern VAR
Byte
Digitl VAR
PORTA.O
Digit2 VAR
PORTA. 1
Pbutton VAR
PORTB.7
i VAR
Byte
' Cnt is a byte variable
' Digit is a byte variable
' Pattern is a byte variable
' Digit 1 enable bit
' Digit 2 enable bit
' Push button is bit 7 of PORTB
' i is a byte variable
' START OF MAIN PROGRAM
CMCON = 7
TRISA =
TRISB = $80
' Enable TMRO timer interrupts
INTCON = %00 100000
OPTION_REG = %000001 1 1
TMRO = 217
ON INTERRUPT GOTO ISR
INTCON = % 10 100000
' RA0-RA3 are digital I/O
' Set PORTA as output
' Bit 7 of PORTB input, others outputs
' Enable TMRO interrupts
' Initialise the prescale
' Load TMRO register
' Enable Interrupts
Cnt =
' Initialise event counter to
LOOP:
BUTTON Pbutton, 0, 255,0, i, 0, LOOP
debounce switch
Cnt = Cnt + 1
GOTO LOOP
' Wait until push-button is pressed and
' Increment event counter
' Continue
This is the Interrupt Service Routine (ISR). The program jumps to this
routine whenever a timer interrupt is generated. Inside this routine the
value of variable Cnt is displayed.
DISABLE
ISR:
TMRO = 217
' Disable further interrupts
Figure 5.66 (Continued)
PicBasic and PicBasic Pro projects 209
Digit = Cnt DIG 1 ' Get 10s digit
LOOKUP Digit, [$3F, $06, $5B, $4F, $66, $6D, $7D, $07, $7F, $6F], Pattern
Pattern = Pattern A $FF ' Invert bits of variable Pattern
PORTB = Pattern ' Display 10s digit
Digit2 = ' Disable digit 2
Digit 1 = 1 ' Enable digit 1
Pause 5 ' Wait 5ms
Digit = Cnt DIG ' Get Is digit
LOOKUP Digit, [$3F, $06, $5B, $4F, $66, $6D, $7D, $07, $7F, $6F], Pattern
Pattern = Pattern A $FF ' Invert bits of variable Pattern
Digit 1 = ' Disable digit 1
PORTB = Pattern ' Display Is digit
Digit2 = 1 ' Enable digit 2
PAUSE 1 'Wait lms
INTCON.2 = ' Re-enable TMRO interrupts
RESUME ' Return to main program
ENABLE ' Enable interrupts
END ' End of program
Figure 5.66 PicBasic Pro program of Project 14
210 PIC BASIC projects
Project 15
Project title:
Project description:
4-digit LED display with serial driver - counter project
In this project a 4-digit serial 7-segment display is used as a decimal
counter. The display counts up by one every second from 0000 to 9999.
When it reaches 9999, it goes back to 0000 and the process continues
forever.
Hardware:
Multiplexed 7-segment displays are so important in many display-based
applications that several manufacturers have designed multi-digit, multi-
plexed displays with built-in drivers. One such display is the 4-digit multi-
plexed 7-segment display B08M04N, manufactured by Nexus Machines
Ltd. This is a family of displays with sizes ranging from 8 to 38 mm and
available in red, green, and yellow colours.
In this project, a B08M04N-R red colour 8 mm 4-digit 7-segment display
is used. Figure 5.67 shows the picture of this display.
Figure 5.67 B08M04N-R display
The display has 9 pins as shown in Table 5.6. The on-board driver chip has
a serial input format that features serial data, clock and chip enable. A sin-
gle + 5 V supply is normally used, although the unit will work with a sup-
ply as high as + 10 V. Serial data is sent as 36 bits of segment information
where a logic 1 turns a segment ON. The displays have 2 spare outputs
that can be used for driving external LEDs, where the LED current is pro-
grammed via an on-board resistor.
PicBasic and PicBasic Pro projects 211
Table 5.6 B08M04N display pin configuration
Pin number
Description
1
LED 1 drive
2
LED 2 drive
3
Chip enable
4
Data
5
Clock
6
Vdd(+5V)
7
Brightness
8
Gnd(OV)
9
Vied
Table 5.7 shows how data should be sent to the display unit. First, a start
bit (logic 1) is sent. After this, the segments a to g and the decimal point
of each digit are sent consecutively starting from digit 1 , which is the digit
at the right-most position. The start bit and the 4-digit display data is sent
in 33 bits. Then the bits for the 2 LED are sent (a logic 1 turns on an
LED). The last bit sent is a NULL bit.
Table 5.7 Display segment data
BitO
START
Bit 9
A2
Bit 17
A3
Bit 25
A4
Bit 33
LED 1
Bitl
Al
Bit 10
B2
Bit 18
B3
Bit 26
B4
Bit 34
LED2 2
Bit 2
Bl
Bit 11
C2
Bit 19
C3
Bit 27
C4
Bit 35
Null
Bit 3
CI
Bit 12
D2
Bit 20
D3
Bit 28
D4
Bit 4
Dl
Bit 13
E2
Bit 21
E3
Bit 29
E4
Bit 5
El
Bit 14
F2
Bit 22
F3
Bit 30
F4
Bit 6
Fl
Bit 15
G2
Bit 23
G3
Bit 31
G4
Bit 7
Gl
Bit 16
DP2
Bit 24
DP3
Bit 32
DP4
Bit 8
DPI
The display control is summarised below (note that each bit should be fol-
lowed by a clock bit):
Send START bit (logic 1)
Send A 1 to Gl of digit 1 (right-most digit)
Send decimal point (DPI) of digit 1
212 PIC BASIC projects
• Send A2 to G2 of digit 2
• Send decimal point (DP2) of digit 2
• Send A3 to G3 of digit 3
• Send decimal point (DP3) of digit 3
• Send A4 to G4 of digit 4 (left-most digit)
• Send decimal point (DP4) of digit 4
• Send LED 1 bit
• Send LED2 bit
• Send a NULL bit.
The relationship between a digit number and the segments to be turned on
to display this number is given in Table 5.8. For example, to display num-
ber 4 in a digit, we have to send the hexadecimal number $66 to the digit,
i.e. bit pattern "01 1001 10". The segment of each digit must be sent first,
i.e. the bits must be shifted left as they are sent to the display. A display is
blank if a is sent to all of its segments. This can be useful when we want
to turn off a leading zero when displaying a number. For example, num-
ber "23" can be displayed as "0023" or "023" or as "23" where the spaces
correspond to blank characters. Leading zeroes are usually not shown in
displays and the correct format is "23".
Table 5.8 Relationship between segments and numbers
Number to display
abcdefgdp
Number (Hex)
1111110
$FC
1
110 1111
$60
2
11011010
$DA
3
11110010
$F2
4
01100110
$66
5
10 110 110
$B6
6
10 111110
$BE
7
1 1 100000
$E0
8
11111110
$FE
9
11110110
$F6
As an example, suppose that we wish to display number 2478 with both
LEDs turned off. The following data should then be sent to the displays:
Send a START bit
Send bit pattern of hexadecimal $FE (i.e. "111111 10") with the MSB
bit sent first to display 8 on digit 1
PicBasic and PicBasic Pro projects 213
• Send bit pattern of hexadecimal $E0 (i.e. "1 1 100000") with the MSB
bit sent first to display 7 on digit 2
• Send bit pattern of hexadecimal $66 (i.e. "01100110") with the MSB
bit sent first to display 4 on digit 3
• Send bit pattern of hexadecimal $DA (i.e. "1 1011010") with the MSB
bit sent first to display 2 on digit 4
• Send for LED 1 to turn off LED 1
• Send for LED 2 to turn off LED 2
• Send as the NULL bit.
That is, the following 36 bits should be sent to the display with a clock bit
sent after each bit (a space character is used between each digit data for
clarity):
"1 11111110 11100000 01100110 11011010 000"[sl]
Similarly, for example, number 34 with leading zeroes and with both LEDs
turned on can be displayed by sending the following bit pattern to the
display:
• Send a START bit
• Send bit pattern of hexadecimal $66 (i.e. "01100110") with the MSB
bit sent first to display 4 on digit 1
• Send bit pattern of hexadecimal $F2 (i.e. "11110010") with the MSB
bit sent first to display 3 on digit 2
• Send bit pattern (i.e. "00000000") to blank digit 3
• Send bit pattern (i.e. "00000000") to blank digit 4
• Send 1 for LED 1 to turn on LED 1
• Send 1 for LED 2 to turn on LED 2
• Send as the NULL bit terminator.
That is, the following 36 bits should be sent to the display with a clock bit
sent after each bit (a space character is used between each digit data for
clarity):
"1 01100110 11110010 00000000 00000000 1 1 0"[s2]
The circuit diagram of Project 15 is shown in Figure 5.68. In this project
a PIC16F627-type microcontroller is used with 4 MHz internal clock and
internal power-on reset. Display data and clock are connected to bit 6 (RB6)
and bit 7 (RB7) of PORTB, respectively.
The project built on a breadboard is shown in Figure 5.69. Note that the
project is very simple and consists of only a few connections.
214 PIC BASIC projects
9V ' 0.33 MF= =
78L05
Battery
^
+5V
=b0.01pF
14
Vdd
RB6
RB7
PIC
16F627
Vss
12
13
Data
Clock
VDD
B08M04N-R
CE GND
8
4-Digit 7-Segment Display
1.
Figure 5.68 Circuit diagram of Project 15
Figure 5.69 Project built on a breadboard
Flow diagram:
The flow diagram of the project is shown in Figure 5.70. At the beginning
of the program PORTB pins are configured as outputs and the states of
LED 1 and LED 2 are set as required. Then the bit pattern to be sent to the
display to show the value of variable Cut is determined and this data is
sent to the display. The program then waits for 1 s, increments Cnt by one,
and this process is repeated forever. Thus, the display shows 000 001 002 . . .
998 999 000 001 ....
PicBasic and PicBasic Pro projects 215
BEGIN
w
Configure PORT B
as output
•y*
Set LED 1 and
LED 2 states
T
Cnt =
T
Determine pattern to be sent
to digits D1 , D2, D3 and D4
■"
Send Data to digits
D1, D2, D3andD4
^
f
Wait 1 second
i
f
Cnt = Cnt + 1
i
f
Figure 5.70 Flow diagram of Project 15
Software:
PicBasic
Figure 5.71 shows the PicBasic program listing. At the beginning of the
program various program variables are configured as bytes or words. The
main program starts by clearing TRISB register so that PORTB pins are
configured as outputs. Variable Cnt is also cleared to zero since the count
will start from 0. The program loop starts with label NXT Here, the 4
digits of variable Cnt are extracted by dividing Cnt repeatedly by the powers
of 10 and taking the decimal value and the remainder (PicBasic does not
support the DIG statement which is available only on PicBasic Pro). After
the digits are obtained, subroutine CONVERT is called to find the 7-segment
bit pattern of each digit. Variables Dl, D2, D3, and D4 store the bit patterns
to be sent to each digit of the display.
216 PIC BASIC projects
4-DIGIT 7-SEGMENT LED DISPLAY
In this project a B08M04 type 4-digit 7-segment LED displays is used.
The program counts up by one every second. LED 1 and LED 2 are turned
off in this example.
The display digits are organised as follows:
D4 D3 D2 Dl
Data is sent: Dl first, then D2, then D3 and finally D4
A PIC16F627 type microcontroller is used in the project with 4MHz
internal clock and internal reset.
The connection between the display and the microcontroller is as follows:
(display CE pin is connected to ground permanently)
RB6 Display DATA
RB7 Display CLOCK
Author: Dogan Ibrahim
Date: October, 2005
Compiler: PicBasic
File: LED25.BAS
Modifications
SYMBOLS
Symbol TRISB = $86 ' TRISB address
Symbol PORTB = $06 ' PORTB address
Symbol Pattern = BO ' Pattern is a byte variable
Symbol I = B 1 ' Loop counter variable
Symbol Digit = B2 ' Digit is a byte variable
Figure 5.71 (Continued)
PicBasic and PicBasic Pro projects 217
Symbol Dl = B3
Symbol D2 = B4
Symbol D3 = B5
Symbol D4 = B6
Symbol LED 1 = B7
Symbol LED2 = B8
Symbol Cnt = W6
Symbol Temp = W7
Symbol DATA = Pin6
Symbol CLK = 7
' START OF MAIN PROGRAM
POKE TRISB,
LED1 =0
LED2 =
' Digit 1 pattern
' Digit 2 pattern
' Digit 3 pattern
' Digit 4 pattern
' Display LED 1 data
' Display LED 2 data
' Cnt is a word variable
' Temp is a word variable
' Display Data is RB6
' Display CLOCK is RB7
' Set PORTB as output
' LED 1 is to be off
' LED 2 is to be off
Cnt =
NXT:
Digit = Cnt/ 1000
GOSUB CONVERT
D4 = Pattern
Temp = Cnt// 1000
Digit = Temp/ 100
GOSUB CONVERT
D3 = Pattern
Temp = Cnt// 100
Digit = Temp/ 10
GOSUB CONVERT
D2 = Pattern
Digit = Temp// 10
GOSUB CONVERT
Dl = Pattern
' Send data to the display
GOSUB SEND_START
Pattern = D1
Figure 5.71 (Continued)
' Number to display in Cnt
' Get 1000s digit
' Get segments to turn on
' Pattern for 1000s digit
' Find remainder
' Get 100s digit
' Get segments to turn on
' Pattern for 100s digit
' Find remainder
' Get 10s digit
' Get segments to turn on
' Pattern for 10s digit
' Find remainder
' get segments to turn on
' Pattern for 1 s digit
' Send START bit
218 PIC BASIC projects
GOSUB DISPLAY ' Send Is digit
Pattern = D2
GOSUB DISPLAY ' Send 10s digit
Pattern = D3
GOSUB DISPLAY ' Send 100s digit
Pattern = D4
GOSUB DISPLAY ' Send 1000s digit
GOSUB SEND_LEDS ' Send LED bits
GOSUB SEND_TERM ' Send TERMINATOR bit
PAUSE 1000 ' Wait 1 second
Cnt = Cnt + 1 ' Increment count
GOTO NXT ' Continue counting and displaying
CONVERT:
' Find the bit pattern to be sent to the display in order to turn on the correct segments
' to display the required number. Digit contains a number between and 9 and
' on return from LOOKUP statement, Pattern contains the bit pattern to send to
' PORTB to display the required number in Digit.
LOOKUP Digit, ($FC, $60, $DA, $F2, $66, $B6, $BE, $E0, $FE, $F6), Pattern
RETURN
SEND_START:
' This subroutine sends a START bit to the display. START bit is a logic 1
DATA = 1 ' Data = 1
TOGGLE CLK ' CLK = 1
TOGGLE CLK ' CLK =
RETURN
SEND_TERM:
' This subroutine sends a TERMINATOR bit to the display. TERMINATOR bit is a logic
DATA = ' Data =
TOGGLE CLK ' CLK = 1
TOGGLE CLK ' CLK =
RETURN
Figure 5.71 (Continued)
PicBasic and PicBasic Pro projects 219
SEND_LEDS:
' This subroutine sends the two LED data to the display
DATA = LED 1
TOGGLE CLK
TOGGLE CLK
DATA = LED2
TOGGLE CLK
TOGGLE CLK
RETURN
DISPLAY:
' This subroutine sends data and clock bits to the display. Data bits are sent by left shifting
' the value in variable Pattern. A clock pulse is sent after sending each data bit.
FOR I = 1 TO 8
DATA = Bit7 ' Get bit 7 of Pattern
TOGGLE CLK ' CLK = 1
Pattern = Pattern * 2 ' Shift left pattern 1 digit
TOGGLE CLK ' CLK =
NEXT I
RETURN
END ' End of program
Figure 5.71 PicBasic program of Project 15
Subroutine SEND_START is called to send the START bit to the display.
Then the bit pattern of each digit is sent, starting with digit 1 . After send-
ing the four-digit data, subroutine SEND_LEDS is called to send the two
LED bit data. Data transfer is complete when the terminator NULL char-
acter is sent by calling subroutine SEND_TERM.
The program given in Figure 5.71 can be improved and made easier to
understand if the display subroutines are all collected and stored inside a
common subroutine. This is shown in Figure 5.72. Here, a subroutine
called DISPLAY is created and all the display related programs are stored
inside this subroutine. The main program consists of the counter Cnt only
which is incremented every second. Subroutine DISPLAY is then called
to display the value of Cnt. The advantage of this approach is that the
DISPLAY subroutine can be used in other programs after it has been
tested and working correctly.
220 PIC BASIC projects
4-DIGIT 7-SEGMENT LED DISPLAY
In this project a B08M04 type 4-digit 7-segment LED displays is used.
The program counts up by one every second. LED 1 and LED 2 are turned
off in this example.
The display digits are organised as follows:
D4 D3 D2 Dl
Data is sent: Dl first, then D2, then D3 and finally D4
A PIC16F627 type microcontroller is used in the project with 4MHz
internal clock and internal reset.
The connection between the display and the microcontroller is as follows:
(display CE pin is connected to ground permanently)
RB6 Display DATA
RB7 Display CLOCK
Author: Dogan Ibrahim
Date: October, 2005
Compiler: PicBasic
File: LED26.BAS
Modifications
SYMBOLS
Symbol TRISB = $86 ' TRISB address
Symbol PORTB = $06 ' PORTB address
Symbol Pattern = BO ' Pattern is a byte variable
Symbol I = B 1 ' Loop counter variable
Symbol Digit = B2 ' Digit is a byte variable
Figure 5.72 (Continued)
PicBasic and PicBasic Pro projects 22 1
Symbol Dl = B3
Symbol D2 = B4
Symbol D3 = B5
Symbol D4 = B6
Symbol LED 1 = B7
Symbol LED2 = B8
Symbol Cnt = W6
Symbol Temp = W7
Symbol DATA = Pin6
Symbol CLK = 7
' START OF MAIN PROGRAM
POKE TRISB,
LED1 =0
LED2 =
Cnt =
NXT: GOSUB DISPLAY
PAUSE 1000
Cnt = Cnt + 1
GOTO NXT
' Digit 1 pattern
' Digit 2 pattern
' Digit 3 pattern
' Digit 4 pattern
' Display LED 1 data
' Display LED 2 data
' Cnt is a word variable
' Temp is a word variable
' Display Data is RB6
' Display CLOCK is RB7
' Set PORTB as output
' LED 1 is to be off
' LED 2 is to be off
' Number to display in Cnt
' Display number in Cnt
' Wait 1 second
' Increment count
' Continue counting and displaying
SUBROUTINES
DISPLAY:
' This subroutine displays the number in variable Cnt on the 4-digit 7-segment display
Digit = Cnt/ 1000
GOSUB CONVERT
D4 = Pattern
Temp = Cnt// 1000
Digit = Temp/ 100
GOSUB CONVERT
D3 = Pattern
Temp = Cnt// 100
Digit = Temp/ 10
GOSUB CONVERT
D2 = Pattern
Figure 5.72 (Continued)
' Get 1000s digit
' Get segments to turn on
' Pattern for 1000s digit
' Find remainder
'Get 100s digit
' Get segments to turn on
' Pattern for 100s digit
' Find remainder
' Get 10s digit
' Get segments to turn on
' Pattern for 10s digit
222 PIC BASIC projects
Digit = Temp // 10 ' Find remainder
GOSUB CONVERT ' get segments to turn on
Dl = Pattern ' Pattern for Is digit
' Send data to the display
GOSUB SEND_START ' Send START bit
Pattern = D1
GOSUB SEGMENTS ' Send Is digit
Pattern = D2
GOSUB SEGMENTS ' Send 10s digit
Pattern = D3
GOSUB SEGMENTS ' Send 100s digit
Pattern = D4
GOSUB SEGMENTS ' Send 1000s digit
GOSUB SEND_LEDS ' Send LED bits
GOSUB SEND_TERM ' Send TERMINATOR bit
RETURN
CONVERT:
Find the bit pattern to be sent to the display in order to turn on the correct segments
to display the required number. Digit contains a number between and 9 and
on return from LOOKUP statement, Pattern contains the bit pattern to send to
PORTB to display the required number in Digit.
LOOKUP Digit, ($FC, $60, $DA, $F2, $66, $B6, $BE, $E0, $FE, $F6), Pattern
RETURN
SEND_START:
t
' This subroutine sends a START bit to the display. START bit is a logic 1
6
DATA = 1 ' Data = 1
TOGGLE CLK ' CLK = 1
TOGGLE CLK ' CLK =
RETURN
SEND_TERM:
.
' This subroutine sends a TERMINATOR bit to the display. TERMINATOR bit is a logic
DATA = ' Data =
TOGGLE CLK ' CLK = 1
TOGGLE CLK ' CLK =
RETURN
Figure 5.72 (Continued)
PicBasic and PicBasic Pro projects 223
SEND_LEDS:
' This subroutine sends the two LED data to the display
DATA = LED 1
TOGGLE CLK
TOGGLE CLK
DATA = LED2
TOGGLE CLK
TOGGLE CLK
RETURN
SEGMENTS:
' This subroutine sends data and clock bits to the display. Data bits are sent by left shifting
' the value in variable Pattern. A clock pulse is sent after sending each data bit.
FOR I = 1 TO 8
DATA = Bit7 ' Get bit 7 of Pattern
TOGGLE CLK ' CLK = 1
Pattern = Pattern * 2 ' Shift left pattern 1 digit
TOGGLE CLK ' CLK =
NEXT I
RETURN
END ' End of program
Figure 5.72 Improved PicBasic program of Project 15
PicBasic Pro
Figure 5.73 shows the program listing. The PicBasic Pro program is much
smaller and also easier to understand than the PicBasic program. The digits
of variable Cnt are found using the PicBasic Pro DIG statement. DIG
returns the Is digit of a variable, DIG 1 returns the 10s digit and so on.
PicBasic Pro also supports the SHIFTOUT statement which is used to
send data and clock bits to the display. The Mode parameter of SHIFTOUT
statement is chosen 1 so that the data is shifted out highest bit first.
The display related code is stored inside a subroutine called DISPLAY.
Main program consists of the counter Cnt only which is incremented every
second and subroutine DISPLAY is called to display its value.
224 PIC BASIC projects
4-DIGIT 7-SEGMENT LED DISPLAY
In this project a B08M04 type 4-digit 7-segment LED displays is used.
The program counts up by one every second. LED 1 and LED 2 are turned
off in this example.
The display digits are organised as follows:
D4 D3 D2 Dl
Data is sent: Dl first, then D2, then D3 and finally D4
A PIC16F627 type microcontroller is used in the project with 4MHz
internal clock and internal reset.
The connection between the display and the microcontroller is as follows:
(display CE pin is connected to ground permanently)
RB6 Display DATA
RB7 Display CLOCK
In this program the leftmost LEDs which are zero are blanked so that for example
number 25 is displayed as "25" and not as "0025"
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED27.BAS
Modifications
DEFINITIONS
Pattern VAR Byte ' Pattern is a byte variable
I VAR Byte ' Loop counter variable
Digit VAR Byte ' Digit is a byte
Figure 5.73 (Continued)
PicBasic and PicBasic Pro projects 225
LED1 VARBit
LED2 VAR Bit
Cnt VAR Word
Symbol DATA_PIN = PORTB.6
Symbol CLK_PIN = PORTB.7
' Display LED 1 data
' Display LED 2 data
' Cnt is a word variable
' Display Data is RB6
' Display CLOCK is RB7
' START OF MAIN PROGRAM
TRISB =
LED1 =0
LED2 =
Cnt =
NXT: GOSUB DISPLAY
PAUSE 1000
Cnt = Cnt + 1
GOTO NXT
DISPLAY:
' Set PORTB as output
' LED 1 is to be off
' LED 2 is to be off
' Number to display in Cnt
' Display number in Cnt
' Wait 1 second
' Increment count
' Continue counting and displaying
SUBROUTINES
This subroutine displays the number in variable Cnt on the 4-digit 7-segment display
Send START bit
DATA_PIN = 1
PULSOUT CLK_PIN, 1
' Data = 1
' Send a clock
' Send digit bits
FOR I = TO 3
Digit = Cnt DIG I ' Get digits of variable Cnt
LOOKUP Digit, [$FC, $60, $DA, $F2, $66, $B6, $BE, $E0, $FE, $F6], Pattern
SHIFTOUT DATA_PIN, CLK_PIN, 1, [ Pattern ]
NEXT I
' Send LED1 and LED 2 bits
DATA_PIN = LED1
PULSOUT CLK_PIN,1
DATA_PIN = LED2
PULSOUT CLK_PIN,1
Figure 5.73 (Continued)
' Data = LED 1
' Send clock
' Data = LED 2
' Send clock
226 PIC BASIC projects
' Send TERMINATOR bit
DATA_PIN =
PULSOUTCLK_PIN,l
RETURN
' Data =
' Send clock
END
Figure 5.73 PicBasic Pro program of Project 15
' End of program
PicBasic and PicBasic Pro projects 227
Project 1 6
Project title:
Project description:
Hardware:
Flow diagram:
4-digit LED display with serial driver - counter project with leading
zeroes blanked
This project is very similar to Project 15 where a 4-digit 7-segment display
is used as a counter. In this project, the leading zeroes of the display are
blanked. Thus, for example, number "67" is displayed as "67", number "5"
is displayed as "5", and so on.
The hardware and the circuit diagram of the project is as in Figure 5.68
where the display is controlled from bit 6 and bit 7 of PORTB.
The flow diagram of the project is very similar to the flow diagram given
in Figure 5.70. Here, the difference is that the leading zeroes are blanked
by sending zeroes to all of their segments. Figure 5.74 shows the flow dia-
gram of the project.
C BEGIN J
i
'
Configure PORTB
as output
i
'
Set LED 1 and
LED 2 states
i
'
Cnt =
1
'
Determine pattern to be sent
to digits D1 , D2, D3 and D4
'
'
Clear any leading
zeroes
i
'
Send Data to digits
D1, D2, D3andD4
'
'
Wait 1 second
^
'
Cnt = Cnt + 1
1
'
Figure 5.74 Flow diagram of Project 16
228 PIC BASIC projects
Software: PicBasic
Figure 5.75 shows the PicBasic program listing. The program is very
similar to the one given in Figure 5.72. Here, the values of leading digits
are checked and if they are zero, the segments of these digits are cleared
to zeroes. Leading zero checking is done by introducing the following
code just before sending the segment data to the display:
IF D4 = $FC THEN BL4
GOTO CONT
BL4:
D4 =
IF D3 = $FC THEN BL3
GOTO CONT
BL3:
D3 =
IF D2 = $FC THEN BL2
GOTO CONT
BL2:
D2 =
CONT
m
If digit 4 bit pattern (D4) is equal to hexadecimal $FC then this digit is
zero and since it is the left-most digit, it is blanked by clearing D4. If both
D4 and D3 bit patterns are zero then both displays are blanked. Finally, if
D4, D3, and D2 bit patterns are zero then all three digits are blanked.
4-DIGIT 7-SEGMENT LED DISPLAY COUNTER WITH BLANKING
In this project a B08M04 type 4-digit 7-segment LED displays is used.
The program counts up by one every second. LED 1 and LED 2 are turned
off in this example.
The display digits are organised as follows:
D4 D3 D2 Dl
Data is sent: Dl first, then D2, then D3 and finally D4
Figure 5.75 (Continued)
PicBasic and PicBasic Pro projects 229
A PIC16F627 type microcontroller is used in the project with 4MHz
internal clock and internal reset.
The connection between the display and the microcontroller is as follows:
(display CE pin is connected to ground permanently)
RB6 Display DATA
RB7 Display CLOCK
In this program the leftmost LEDs which are zero are blanked so that for example
number 25 is displayed as "25" and not as "0025"
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
LED28.BAS
Modifications
SYMBOLS
Symbol TRISB = $86 ' TRISB address
Symbol PORTB = $06 ' PORTB address
Symbol Pattern = B0 ' Pattern is a byte variable
Symbol I = B 1 ' Loop counter variable
Symbol Digit = B2 ' Digit is a byte variable
Symbol Dl = B3 ' Digit 1 pattern
Symbol D2 = B4 ' Digit 2 pattern
Symbol D3 = B5 ' Digit 3 pattern
Symbol D4 = B6 ' Digit 4 pattern
Symbol LED1 = B7 ' Display LED 1 data
Symbol LED2 = B8 ' Display LED 2 data
Symbol Cnt = W6 ' Cnt is a word variable
Symbol Temp = W7 ' Temp is a word variable
Symbol DATA = Pin6 ' Display Data is RB6
Symbol CLK = 7 ' Display CLOCK is RB7
Figure 5.75 (Continued)
230 PIC BASIC projects
' START OF MAIN PROGRAM
POKE TRISB,
LED1 =0
LED2 =
Cnt =
NXT: GOSUB DISPLAY
PAUSE 1000
Cnt = Cnt + 1
GOTO NXT
' Set PORTB as output
' LED 1 is to be off
' LED 2 is to be off
' Number to display in Cnt
' Display number in Cnt
' Wait 1 second
' Increment count
' Continue counting and displaying
SUBROUTINES
DISPLAY:
' This subroutine displays the number in variable Cnt on the 4-digit 7-segment display
Digit = Cnt/ 1000
GOSUB CONVERT
D4 = Pattern
Temp = Cnt // 1000
Digit = Temp / 100
GOSUB CONVERT
D3 = Pattern
Temp = Cnt // 100
Digit = Temp / 10
GOSUB CONVERT
D2 = Pattern
Digit = Temp// 10
GOSUB CONVERT
Dl = Pattern
' Get 1000s digit
' Get segments to turn on
' Pattern for 1000s digit
' Find remainder
' Get 100s digit
' Get segments to turn on
' Pattern for 100s digit
' Find remainder
' Get 10s digit
' Get segments to turn on
' Pattern for 10s digit
' Find remainder
' get segments to turn on
' Pattern for Is digit
' Send data to the display. First find out if there are any leading zeroes and
' blank them.
IF D4 = $FC THEN BL4
GOTO CONT
Figure 5.75 (Continued)
' If Digit D4 is zero...
' Otherwise continue
PicBasic and PicBasic Pro projects 23 1
BL4:D4 =
IF D3 = $FC THEN BL3
GOTO CONT
BL3:D3=0
IF D2 = $FC THEN BL2
GOTO CONT
BL2: D2 =
' Blank D4
' If Digit D3 is zero...
' Otherwise continue
' Blank D3
'IfDigitD2isO...
' Otherwise continue
' Blank D2
CONT:
GOSUB SEND_START
Pattern = D1
GOSUB SEGMENTS
Pattern = D2
GOSUB SEGMENTS
Pattern = D3
GOSUB SEGMENTS
Pattern = D4
GOSUB SEGMENTS
GOSUB SEND_LEDS
GOSUB SEND TERM
' Send START bit
' Send Is digit
' Send 10s digit
' Send 100s digit
' Send 1000s digit
' Send LED bits
' Send TERMINATOR bit
CONVERT:
Find the bit pattern to be sent to the display in order to turn on the correct segments
to display the required number. Digit contains a number between and 9 and
on return from LOOKUP statement, Pattern contains the bit pattern to send to
PORTB to display the required number in Digit.
LOOKUP Digit, ($FC, $60, $DA, $F2, $66, $B6, $BE, $E0, $FE, $F6), Pattern
RETURN
SEND_START:
' This subroutine sends a START bit to the display. START bit is a logic 1
DATA = 1
TOGGLE CLK
TOGGLE CLK
RETURN
' Data = 1
' CLK = 1
' CLK =
SEND_TERM:
' This subroutine sends a TERMINATOR bit to the display. TERMINATOR bit is a logic
Figure 5.75 (Continued)
232 PIC BASIC projects
DATA = ' Data =
TOGGLE CLK ' CLK = 1
TOGGLE CLK ' CLK =
RETURN
SEND_LEDS:
' This subroutine sends the two LED data to the display
DATA = LED 1
TOGGLE CLK
TOGGLE CLK
DATA = LED2
TOGGLE CLK
TOGGLE CLK
RETURN
SEGMENTS:
' This subroutine sends data and clock bits to the display. Data bits are sent by left shifting
' the value in variable Pattern. A clock pulse is sent after sending each data bit.
FOR I = 1 TO 8
DATA = Bit7 ' Get bit 7 of Pattern
TOGGLE CLK ' CLK = 1
Pattern = Pattern * 2 ' Shift left pattern 1 digit
TOGGLE CLK ' CLK =
NEXT I
RETURN
END ' End of program
Figure 5.75 PicBasic program of Project 16
PicBasic Pro
Figure 5.76 shows the PicBasic Pro program listing which is again smaller
and also more efficient than the PicBasic program. Leading zero digits are
cleared by checking each leading digit before sending data to it. Leading
zero checking is performed as follows:
The bit pattern for all the digit segments are found and if a leading digit is
zero and the digit to its left is also zero (variable First is 1), then variable
Pattern is cleared to zero. Byte array "T[ ]" stores the bit patterns of all the
digits. A "FOR" loop is formed to shift out the segment data of each digit,
with digit 1 bits shifted out first.
PicBasic and PicBasic Pro projects 233
4-DIGIT 7-SEGMENT COUNTER WITH BLANKING DISPLAY
In this project a B08M04 type 4-digit 7-segment LED displays is used.
The program counts up by one every second. LED 1 and LED 2 are turned
off in this example.
The display digits are organised as follows:
D4 D3 D2 Dl
Data is sent: Dl first, then D2, then D3 and finally D4
A PIC16F627 type microcontroller is used in the project with 4MHz
internal clock and internal reset.
The connection between the display and the microcontroller is as follows:
(display CE pin is connected to ground permanently)
RB6 Display DATA
RB7 Display CLOCK
In this program the leftmost LEDs which are zero are blanked so that for example
number 25 is displayed as "25" and not as "0025"
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED29.BAS
Modifications
DEFINITIONS
Pattern VAR Byte ' Pattern is a byte variable
I VAR Byte ' Loop counter variable
Digit VAR Byte ' Digit is a byte
Figure 5.76 (Continued)
234 PIC BASIC projects
First VAR Byte
' Blanking checking variable
T VAR Byte[4]
' Digit segment bit patterns
LED1 VAR Bit
' Display LED 1 data
LED2 VAR Bit
' Display LED 2 data
Cnt VAR Word
' Cnt is a word variable
Symbol DATA_PIN =
PORTB.6
' Display Data is RB6
Symbol CLK_PIN = PORTB.7
' Display CLOCK is RB7
' START OF MAIN PROGRAM
TRISB =
LED1 =0
LED2 =
Cnt =
NXT: GOSUB DISPLAY
PAUSE 1000
Cnt = Cnt + 1
GOTO NXT
' Set PORTB as output
' LED 1 is to be off
' LED 2 is to be off
' Number to display in Cnt
' Display number in Cnt
' Wait 1 second
' Increment count
' Continue counting and displaying
SUBROUTINES
DISPLAY:
This subroutine displays the number in variable Cnt on the 4-digit 7-segment display
Send START bit
DATA_PIN = 1
PULSOUT CLK_PIN, 1
' Data = 1
' Send a clock
Find out if blanking of leading digits are required or not. Since digit 1 is sent first, we
have to find all the digits and determine if blanking of any digit is required. Array T[I]
stores the bit pattern of each digit
First = 1 ' First time round the loop
FORI = 3TO0STEP-l
Digit = Cnt DIG I ' Get digits of variable Cnt
LOOKUP Digit, [$FC, $60, $DA, $F2, $66, $B6, $BE, $E0, $FE, $F6], Pattern
IF (Digit = 0) AND (First = 1) THEN
Pattern =
ELSE
First =
ENDIF
Figure 5.76 (Continued)
PicBasic and PicBasic Pro projects 235
T[I] = Pattern
NEXT I
IF Cnt = THEN T[0] = $FC ' If Cnt = display in Dl
' Display each digit with blanking leading zeroes. Digit 1 is sent first
FOR I = To 3
SHIFTOUT DATA_PIN, CLK_PIN, 1, [ T[I] ]
NEXT I
' Send LED1 and LED 2 bits
DATA_PIN = LED1
PULSOUTCLK_PIN,l
DATA_PIN = LED2
PULSOUTCLK_PIN,l
' Send TERMINATOR bit
DATA_PIN =
PULSOUTCLK_PIN,l
RETURN
Data = LED 1
Send clock
Data = LED 2
Send clock
Data =
Send clock
END ' End of program
Figure 5.76 PicBasic Pro program of Project 16
236 PIC BASIC projects
Project 17
Project title:
Project description:
Hardware:
4-digit external interrupt- driven event counter
This project can be used to count external events and to display the event
count on a 4-digit display. An event can be an object on a conveyor belt,
number of people entering a building, number of cars entering and leav-
ing a car park, etc. External interrupt input of the microcontroller is used
to detect events. An event is detected when the external interrupt pin
changes state from logic 1 to logic 0. This project shows how the external
interrupt pin of a PIC microcontroller can be used.
The circuit diagram of the project is shown in Figure 5.77. Display is con-
nected to bit 6 and bit 7 of PORTB as in Project 16. Interrupt input of the
microcontroller (INT) is connected to a switch which simulates the
occurrence of an event. The switch is normally at logic 1 and goes to logic
when an external event occurs (i.e. when the switch is pressed).
9V
Battery
0.33 uFd=
78L05
t:
+5V
i
=^0,01mF
10K
14
Push to
Interrupt M
Vdd
RBO/INT
RB6
RB7
PIC
16F627
Vss
12
13
Data
Clock
VDD
B08M04N-R
CE GND
8
4-Digit 7-Segment Display
1.
Figure 5.77 Circuit diagram of Project 17
Flow diagram:
The flow diagram of the project is given in Figure 5.78. At the beginning
of the program event counter variable Cnt is cleared and external inter-
rupts are enabled. The main program then goes into an endless loop
where the value of Cnt is displayed continuously. Whenever an external
interrupt occurs the value of event counter Cnt is incremented by one and
new value of Cnt is displayed by the main program.
PicBasic and PicBasic Pro projects 237
f BEGIN J
ir
CNT =
^
Display CNT
ISR
BEGIN
CNT = CNT + 1
Re-enable interrupts
RETURN
Figure 5.78 Flow diagram of Project 17
Software:
PicBasic
Interrupts are not directly supported from the PicBasic language and thus
only the PicBasic Pro program of this project is given.
PicBasic Pro
Figure 5.79 shows the PicBasic Pro program listing. At the beginning of the
program TRISB is set to 1 so that RBO is configured as input and other bits
of PORTB are configured as outputs. Register OPTION_REG is then con-
figured so that external interrupts are recognised on the falling edge (high
to low transition) of the interrupt input. Register INTCON is configured to
enable external interrupts and the routine starting with label ISR has been
assigned to be the interrupt service routine. Notice that the statement "ON
INTERRUPT GOTO ISR" assigns label ISR to be the starting address of
the interrupt service routine (any other label name can be used here).
Inside the main program variable Cnt is cleared and the program calls to
subroutine DISPLAY to show the value of variable Cnt continuously.
238 PIC BASIC projects
Inside the ISR variable Cnt is incremented by 1, external interrupts are
re-enabled, and the program returns to the main program. Notice that inter-
rupts are disabled just before entering the ISR, and they are re-enabled
just after leaving the ISR.
4-DIGIT INTERRUPT BASED EVENT COUNTER
In this project a B08M04 type 4-digit 7-segment LED displays is used.
A switch is connected to the external interrupt input of the microcontroller.
The program counts external interrupts (i.e. external events) and displays
the result on a 4-digit 7-segment display. Interrupts are detected on the
high to low transition of the interrupt pin (RBO/INT) of the microcontroller.
The display digits are organised as follows:
D4 D3 D2 Dl
Data is sent: Dl first, then D2, then D3 and finally D4
A PIC16F627 type microcontroller is used in the project with 4MHz
internal clock and internal reset.
The connection between the display and the microcontroller is as follows:
(display CE pin is connected to ground permanently)
RB6 Display DATA
RB7 Display CLOCK
In this program the leftmost LEDs which are zero are blanked so that for example
number 25 is displayed as " 25" and not as "0025"
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED30.BAS
Modifications
Figure 5.79 (Continued)
PicBasic and PicBasic Pro projects 239
' DEFINITIONS
Pattern VAR Byte
I VAR Byte
Digit VAR Byte
First VAR Byte
T VAR Byte[4]
LED1 VAR Bit
LED2 VAR Bit
Cnt VAR Word
Symbol DATA_PIN = PORTB.6
Symbol CLK_PIN = PORTB.7
' Pattern is a byte variable
' Loop counter variable
' Digit is a byte
' Blanking checking variable
' Digit segment bit patterns
' Display LED 1 data
' Display LED 2 data
' Cnt is a word variable
' Display Data is RB6
' Display CLOCK is RB7
' START OF MAIN PROGRAM
TRISB = 1
ON INTERRUPT GOTO ISR
OPTION_REG = %0 1000000
LED1 =0
LED2 =
Cnt =
INTCON = % 100 10000
NXT: GOSUB DISPLAY
GOTO NXT
' RB0 is input, others output
' Interrupt service routine
' External interrupt on falling edge of RB0
' LED 1 is to be off
' LED 2 is to be off
' Clear the event counter, Cnt
' Enable external interrupt RB0
' Display number in Cnt
' Continue counting and displaying
' This is the interrupt service routine, ISR. The program jumps here whenever an external
' interrupt (i.e. whenever an event occurs) occurs
DISABLE
ISR:
Cnt = Cnt +1
INTCON = % 10010000
RESUME
ENABLE
' Disable interrupts
' Entry point of the ISR
' Increment event counter, Cnt
' Enable external interrupts
' Resume main program
' Enable interrupts
SUBROUTINES
DISPLAY:
' This subroutine displays the number in variable Cnt on the 4-digit 7-segment display
Figure 5.79 (Continued)
240 PIC BASIC projects
' Send START bit
DATA_PIN = 1 ' Data = 1
PULSOUT CLK_PIN, 1 ' Send a clock
Find out if blanking of leading digits are required or not. Since digit 1 is sent first, we
have to find all the digits and determine if blanking of any digit is required. Array T[I]
stores the bit pattern of each digit
First = 1 ' First time round the loop
FORI = 3TO0STEP-l
Digit = Cnt DIG I ' Get digits of variable Cnt
LOOKUP Digit, [$FC, $60, $DA, $F2, $66, $B6, $BE, $E0, $FE, $F6], Pattern
IF (Digit = 0) AND (First = 1) THEN
Pattern =
ELSE
First =
ENDIF
T[I] = Pattern
NEXT I
IF Cnt = THEN T[0] = $FC ' If Cnt = display in Dl position
' Display each digit with blanking leading zeroes. Digit 1 is sent first
FOR I = To 3
SHIFTOUT DATA_PIN, CLK_PIN, 1, [ T[I] ]
NEXT I
' Send LED1 and LED 2 bits
DATA_PIN = LED 1 ' Data = LED 1
PULSOUT CLK_PIN,1 ' Send clock
DATA_PIN = LED2 ' Data = LED 2
PULSOUT CLK_PIN,1 ' Send clock
1 Send TERMINATOR bit
DATA_PIN = ' Data =
PULSOUT CLK_PIN, 1 ' Send clock
RETURN
END ' End of program
Figure 5.79 PicBasic Pro program of Project 17
PicBasic and PicBasic Pro projects 24 1
Project 18
Project title:
4-digit timer interrupt-driven chronograph
Project description: This project is a chronograph with three push-button switches labelled:
START, STOP, and CLEAR. The chronograph is configured to count up
accurately in 10 ms intervals using the timer interrupts of the microcon-
troller. The count is displayed continuously on a 4-digit 7-segment dis-
play. Counting starts when the START button is pressed, and stops when
the STOP button is pressed. When the counter is in stopped, pressing the
CLEAR button clears the display so that a new count can be started.
Hardware:
The circuit diagram of the project is shown in Figure 5.80. Display is con-
nected to bit 6 and bit 7 of PORTB as in Project 16. START, STOP, and
CLEAR buttons are connected to bit 0, bit 1, and bit 2 of PORTB, respect-
ively. A PIC16F627-type microcontroller is used in this project with
4 MHz internal clock and the internal master clear circuit of the micro-
controller is enabled to minimise external component count.
Flow diagram:
The flow diagram of the project is given in Figure 5.81. At the beginning
of the program event counter variable Cnt is cleared and the program waits
1
jy | 0.33 UF = =
Battery \ ^
78L05
^
+5V
q=0.0lMF
10K
14
START
STOP
°1
+5V,
10K
*1
CLEAR
+5V,
10K
Vdd
RBO
RB6
RB7
PIC
16F627
RB1
Vss
RB2
12
13
Data
Clock
VDD
B08M04N-R
CE GND
8
4-Digit 7-Segment Display
Figure 5.80 Circuit diagram of Project 18
242 PIC BASIC projects
until switch START is pressed. When START is pressed timer interrupt
TMRO is enabled and Cnt is incremented every 10 ms. Counting stops
when the STOP button is pressed. At this mode, pressing the CLEAR
switch clears the display and the process repeats from the beginning.
N
N
N
BEGIN
Configure TMRO
CNT =
Start TMRO and
enable interrupts
Display count
Stop count
ISR
BEGIN
1
-
CNT = CNT + 1
i
'
Re-enable interrupts
'
'
RETURN
Figure 5.81 Flow diagram of Project 18
PicBasic and PicBasic Pro projects 243
Software: PicBasic
Interrupts are not directly supported from the PicBasic language and thus
only the PicBasic Pro program of this project is given.
PicBasic Pro
Figure 5.82 shows the PicBasic Pro program listing. At the beginning of
the program TRISB is set to 7 so that RBO, RB 1, and RB2 are configured
as inputs and other pins of PORTB are configured as outputs. Then, the
ISR address is defined and OPTION_REG register is set so that the
TMRO pre-scaler is 64. The program then waits until the START button
(PSTART) is pressed. When the START button is pressed the timer inter-
rupt is enabled so that Cnt is incremented automatically every 10 ms. The
program also checks to see if the STOP button (PSTOP) is pressed and if
so, jumps to label STP to stop the timer interrupt. The final value of Cnt
can be seen on the display at this point. The BUTTON statement is used
with debouncing to check the state of the push-button switches.
The interrupt service routine starts with label ISR. Inside this routine Cnt
is incremented by 1, TMRO is re-loaded with 100 so that timer interrupts
are generated every 10 ms. Timer interrupt flag (bit 2 of INTCON) is also
cleared inside this routine so that further timer interrupts can be accepted
by the microcontroller. Assuming a 4-MHz clock is used, the timer inter-
rupt TMRO interval is given by
Interval (|jls) = pre-scaler X (256 - TMRO)
with a pre-scaler value of 64 and a TMRO value of 100 the TMRO inter-
val is given by
Interval = 64*(256 - 100) = 9.984 ms
which is close enough to 10ms ... .
4-DIGIT TIMER INTERRUPT BASED CHRONOGRAPH
In this project a B08M04 type 4-digit 7-segment LED display is used.
Three switches are connected to the microcontroller: START, STOP and
CLEAR. When START switch is pressed counting starts with
10ms intervals. When the STOP switch is pressed counting stops.
Figure 5.82 (Continued)
244 PIC BASIC projects
When the count stops, pressing the CLEAR button clears the display,
ready for the next count.
The display digits are organised as follows:
D4 D3 D2 Dl
Data is sent: Dl first, then D2, then D3 and finally D4
A PIC16F627 type microcontroller is used in the project with 4MHz
internal clock and internal reset.
The connection between the display and the microcontroller is as follows:
(display CE pin is connected to ground permanently)
RB6 Display DATA
RB7 Display CLOCK
The switches are connected as follows:
RBO START
RBI STOP
RB2 CLEAR
In this program the leftmost LEDs which are zero are blanked so that for example
number 25 is displayed as "25" and not as "0025"
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic Pro
File:
LED31.BAS
Modifications
DEFINITIONS
Pattern VAR Byte ' Pattern is a byte variable
I VAR Byte ' Loop counter variable
Figure 5.82 (Continued)
PicBasic and PicBasic Pro projects 245
Digit
VAR Byte
First
VAR Byte
temp
VAR Byte
T
VAR Byte[4]
LED1
VAR Bit
LED2
VAR Bit
Cnt
VAR Word
Symbol
DATA_PIN = PORTB.6
Symbol
CLK_PIN = PORTB.7
Symbol
PSTART = PORTB.O
Symbol
PSTOP = PORTB.l
Symbol
PCLEAR = PORTB.2
' Digit is a byte
' Blanking checking variable
' Temporary byte variable
' Digit segment bit patterns
' Display LED 1 data
' Display LED 2 data
' Cnt is a word variable
' Display Data is RB6
' Display CLOCK is RB7
' START button
' STOP button
' CLEAR button
' START OF MAIN PROGRAM
TRISB = 7
ON INTERRUPT GOTO ISR
OPTION_REG = %00000101
LED1 =0
LED2 =
BEGIN:
Cnt =
GOSUB DISPLAY
INTCON = % 100 10000
RB0, RBI, RB2 are inputs, others output
Interrupt service routine
Configure TMR0 for prescaler=64
LED 1 is to be off
LED 2 is to be off
Clear the event counter, Cnt
Display Cnt
Enable timer interrupt TMR0
' Wait until the START button is pressed
BT: temp =
BUTTON PSTART, 0, 255, 0, temp, 1, STRT
GOTO BT
' Goto STRT if START pressed
' START button is pressed. Start the counting
STRT:
TMR0 = 100
INTCON = % 10 100000
WT: GOSUB DISPLAY
IF PSTOP = THEN STP
GOTO WT
Figure 5.82 (Continued)
' count = 64*(256 - 100) = 9984us
' Enable TMR0 interrupts
' Display Cnt
' If STOP switch is pressed
' Repeat
246 PIC BASIC projects
' STOP button is pressed. Stop the counting
STP:
INTCON = ' Stop counting
ST: temp =
BUTTON PCLEAR, 0, 255, 0, temp, 1, BEGIN
GOTO ST
' This is the timer interrupt service routine, ISR. The program jumps here whenever a timer
' interrupt occurs (i.e. every 10ms)
DISABLE ' Disable interrupts
ISR: ' Entry point of the ISR
TMRO =100 ' TMR0 value for 10ms count
Cnt = Cnt + 1 ' Increment event counter, Cnt
INTCON.2 = ' Re-enable TMRO interrupts
RESUME ' Resume main program
ENABLE ' Enable interrupts
' ============================ SUBROUTINES
DISPLAY:
This subroutine displays the number in variable Cnt on the 4-digit 7-segment display
Send START bit
DATA_PIN = 1 ' Data = 1
PULSOUT CLK_PIN, 1 ' Send a clock
Find out if blanking of leading digits are required or not. Since digit 1 is sent first, we
have to find all the digits and determine if blanking of any digit is required. Array T[I]
stores the bit pattern of each digit
First = 1 ' First time round the loop
FORI = 3TO0STEP-l
Digit = Cnt DIG I ' Get digits of variable Cnt
LOOKUP Digit, [$FC, $60, $DA, $F2, $66, $B6, $BE, $E0, $FE, $F6], Pattern
IF (Digit = 0) AND (First = 1) THEN
Pattern =
Figure 5.82 (Continued)
PicBasic and PicBasic Pro projects 247
ELSE
First =
ENDIF
T[I] = Pattern
NEXT I
IF Cnt = THEN T[0] = $FC ' If Cnt = then display in Dl position
' Display each digit with blanking leading zeroes. Digit 1 is sent first
FOR I = To 3
SHIFTOUT DATA_PIN, CLK_PIN, 1, [ T[I] ]
NEXT I
' Send LED1 and LED 2 bits
DATA_PIN = LED1
PULSOUTCLK_PIN,l
DATA_PIN = LED2
PULSOUTCLK_PIN,l
' Send TERMINATOR bit
DATA_PIN =
PULSOUTCLK_PIN,l
RETURN
END
Figure 5.82 PicBasic Pro program of Project 18
Data = LED 1
Send clock
Data = LED 2
Send clock
Data =
Send clock
' End of program
248 PIC BASIC projects
Project 1 9
Project title:
Project description:
Car park control system
This project is a simple car park control system. Two barriers are used,
one at the entry and one at the exit of a car park. When a barrier is lifted
to allow a car to pass through, switches are activated which send logic
pulses to the microcontroller. A 4-digit 7-segment display is connected to
the output of the control system. The system counts the difference of the
number of cars entering and leaving the car park. If the count is less than
100 (assuming the car park can take up to 100 cars) the message SPCS
(i.e. spaces) will be displayed. When the car park is full, the message
FULL will be displayed. Assume that the barriers lift-up automatically
when a vehicle approaches them. Also assume that the entry barrier has a
locking mechanism and this mechanism is enabled to lock the barrier so
that it does not lift-up when the car park is full.
Figure 5.83 shows the block diagram of the car park control system.
ENTRY barrier
EXIT barrier
PIC
Microcontroller
ENTRY barrier
p
• LOCK
4-Digit 7-Segment
Display
fc
►
Figure 5.83 Block diagram of Project 19
Hardware:
The circuit diagram of the project is shown in Figure 5.84. Display is con-
nected to bit 6 and bit 7 of PORTB as in Project 16. ENTRY and EXIT
switches are connected to bit and bit 1 of PORTB, respectively. ENTRY
barrier lock output is connected to bit 2 of PORTB. In Figure 5.84, the
barrier switches are shown as simple push-button switches. Also, the
ENTRY lock mechanism is an output from RB2 and is shown as a small
circle.
In this project a PIC 16F627- type microcontroller is used and the micro-
controller is operated with its 4 MHz internal clock and internal master
clear circuit.
Flow diagram:
The flow diagram of the project is given in Figure 5.85. At the beginning
of the program event counter variable Cnt is cleared and the program
checks the value of Cnt. If Cnt > 100 then the car park is assumed to be
full and message "FULL" is displayed. If on the other hand Cnt < 100
then it is assumed that there are spaces in the car park and message
1
9V ! 0.33 pFzz ;
Battery | H ^ l
78L05
m
+5V
=b0.01 MF
10K
14
ENTR
*
noi
EXIT
[
-°1
+5V
10K
-1
ENTRY
LOCK
a
Vdd
RBO
RB6
RB7
PIC
16F627
RB1
RB2
Figure 5.84 Circuit diagram of Project 19
Vss
12
13
Data
Clock
VDD
B08M04N-R
CE GND
T
4-Digit 7-Segment Display
BEGIN
CNT =
Display FULL
Display SPCS
CNT = CNT + 1
CNT = CNT - 1
Unlock ENTRY
barrier
Lock ENTRY
barrier
Figure 5.85 Flow diagram of Project 19
250 PIC BASIC projects
"SPCS" is displayed. The program then checks the ENTRY switch and
Cnt is incremented when a car enters the car park. Similarly, Cnt is decre-
mented when a car leaves the car park. When the car park is full, the lock
mechanism is activated which stops The ENTRY barrier to open when a
car approaches it. The lock mechanism is disabled as soon as spaces are
available in the car park.
Software: PicBasic
Figure 5.86 shows the PicBasic program listing of Project 19. At the
beginning of the program symbol CAPACITY is assigned to 100 and
TRISB is set to 3 so that bit and bit 1 of PORTB are inputs, other pins
outputs. The main program begins with label BEGIN. Here, if Cnt is
greater than or equal to the CAPACITY, the car park is assumed to be full
and subroutine DFULL is called to display the message FULL. If on the
other hand Cnt is less than the CAPACITY then the car park is assumed to
have spaces and subroutine DSPCS is called to display the message
SPCS. ENTRY and EXIT switches are checked inside the LOOP. When a
vehicle enters the car park, ENTRY switch is activated and program
jumps to label LENTRY Similarly, when a vehicle leaves the car park,
EXIT switch is activated and program jumps to label LEXIT.
Inside subroutine LENTRY, Cnt is incremented by 1 and LOCK is set to
1 if Cnt is greater than or equal to the CAPACITY. The program then
jumps to label BEGIN to repeat the process. Inside the LEXIT subrou-
tine, Cnt is decremented By 1 and LOCK is cleared. The program then
jumps to label BEGIN to repeat the process.
Characters FULL and SPCS are obtained by loading Dl - D4 with the
correct bit patterns for these characters. Table 5.9 shows how to obtain
characters FULL and SPCS by sending hexadecimal data to the display.
Thus, to FULL will be displayed if the following hexadecimal numbers
are sent to the display:
$1C $1C $7C $8E
Similarly, SPCS will be displayed if the following hexadecimal numbers
are sent to the display:
$B6 $9C $CE $B6
Bit patterns are sent to the display using subroutine SHIFTO which sends
out data bits in serial form with clock.
PicBasic and PicBasic Pro projects 25 1
d
FULL
SPCS
Table 5.9 Bit patterns for characters FULL and SPCS
Character
abcdefgdp
Hexadecimal
F
10001 1 10
$8E
U
01111100
$7C
L
0001 1 100
$1C
S
10 110 110
$B6
P
11001110
$CE
C
10011100
$9C
252 PIC BASIC projects
CAR PARK CONTROL SYSTEM
In this project a B08M04 type 4-digit 7-segment LED display is used.
Two switches are connected to the microcontroller inputs: ENTRY switch
and EXIT switch. These switches are operated by the barriers at the
entrance and the exit of the car park. The switches are normally at logic
1 and they go to logic when a barrier is lifted up.
Assume that a barrier lifts up automatically when a vehicle approaches
a barrier. The ENTRY barrier also has a locking mechanism and is
used to lock the barrier when the car park is full. Assume that the lock
is activated when a logic 1 is sent to it.
Assume that the capacity of the car park is 100. If the number of vehicles
inside the car park is less than 100 the the message SPCS (i.e. spaces)
is displayed. If the car park is full (i.e. there are 100 cars inside the car
park), then the message FULL is displayed.
The display digits are organised as follows:
D4 D3 D2 Dl
Data is sent: Dl first, then D2, then D3 and finally D4
A PIC16F627 type microcontroller is used in the project with 4MHz
internal clock and internal reset.
The connection between the display and the microcontroller is as follows:
(display CE pin is connected to ground permanently)
RB6 Display DATA
RB7 Display CLOCK
The switches are connected as follows:
RB0 ENTRY
RBI EXIT
RB2 LOCK
Figure 5.86 (Continued)
PicBasic and PicBasic Pro projects 253
Author:
Dogan Ibrahim
Date:
October, 2005
Compiler:
PicBasic
File:
CAR_PRK1.BAS
Modifications
DEFINITIONS
Symbol TRISB = $86
Symbol PORTB = $06
Symbol
Symbol
Symbol
Symbol
Symbol
Symbol
Symbol
Symbol
Symbol
Symbol
Symbol
Symbol
Symbol
Symbol
Symbol
Pattern = BO
I = B1
temp = B2
LED1 = B3
LED2 = B4
Dl =B5
D2 = B6
D3 = B7
D4 = B8
Cnt = W5
DATA = Pin6
CLK = 7
PENTRY =
PEXIT = 1
LOCK = 2
Symbol CAPACITY = 100
' START OF MAIN PROGRAM
POKE TRISB, 3
LED1 =
LED2 =
Cnt =
BEGIN:
IF Cnt >= CAPACITY THEN LARGER
IF Cnt < CAPACITY THEN SMALLER
Figure 5.86 (Continued)
' TRISB address
' PORTB address
' Loop counter variable
' Temporary byte variable
' Display LED 1 data
' Display LED 2 data
' Digit 1 data
' Digit 2 data
' Digit 3 data
' Digit 4 data
' Display Data is RB6
' Display CLOCK is RB7
' START button
' STOP button
' LOCK output
' Car park capacity is 100 vehicles
' RB0, RB 1 are inputs, others output
' LED 1 is to be off
' LED 2 is to be off
' Clear the car park count
254 PIC BASIC projects
LARGER: GOSUB DFULL
GOTO LOOP
SMALLER: GOSUB DSPCS
' Check if ENTRY barrier is lifted up
LOOP:
temp =
BUTTON PENTRY, 0, 255, 0, temp, 1, LENTRY
temp =
BUTTON PEXIT, 0, 255, 0, temp, 1, LEXIT
GOTO LOOP
' Goto LENTRY if
' ENTRY switch =
' Goto LEXIT if EXIT switch =
' START button is pressed. Start the counting
LENTRY:
LEXIT:
Cnt = Cnt + 1
IF Cnt < CAPACITY THEN BEGIN
HIGH LOCK
GOTO BEGIN
Cnt = Cnt - 1
LOW LOCK
GOTO BEGIN
' A vehicle entered the car park
' Lock the ENTRY barrier
' A vehicle left the car park
' Unlock the ENTRY barrier
DFULL:
DSPCS:
D1=$1C: D2 = $1C:
GOSUB DISPLAY
RETURN
Dl = $B6: D2 = $9C:
GOSUB DISPLAY
RETURN
D3 = $7C:
D3 = $CE:
D4 = $8E
D4 = $B6
DISPLAY:
This subroutine displays the the 4 byte data in D1,D2,D3,D4.
Dl data is sent first to the display.
Send start bit
Figure 5.86 (Continued)
PicBasic and PicBasic Pro projects 255
DATA = 1
TOGGLE CLK
TOGGLE CLK
' Send segment data
B0 = D1
GOSUB SHIFTO
B0 = D2
GOSUB SHIFTO
B0 = D3
GOSUB SHIFTO
B0 = D4
GOSUB SHIFTO
' This subroutine sends the two LED data to the display
DATA = LED1
TOGGLE CLK
TOGGLE CLK
DATA = LED2
TOGGLE CLK
TOGGLE CLK
' Send terminator bit
DATA =
TOGGLE CLK
TOGGLE CLK
RETURN
SHIFTO:
' This subroutine shifts out data with clock
FOR I = 1 TO 8
DATA = Bit7
TOGGLE CLK
Pattern = Pattern * 2
TOGGLE CLK
NEXT I
RETURN
END
Figure 5.86 PicBasic program of Project 19
Data = 1
CLK= 1
CLK =
Display Dl
Display D2
Display D3
Display D4
Data =
CLK= 1
CLK =
' Get bit 7 of Pattern
' CLK = 1
' Shift left pattern 1 digit
' CLK =
' End of program
256 PIC BASIC projects
PicBasic Pro
Figure 5.87 shows the PicBasic Pro program listing. At the beginning of the
program, the capacity of the car park, symbol CAPACITY is assigned value
100. TRISB register is set to 3 so that bit and bit 1 of PORTB are inputs,
the other pins outputs. The main program loop begins with label BEGIN.
Here, if Cnt is greater than or equal to the CAPACITY, the car park is
assumed to be full and subroutine DFULL is called to display the message
FULL. If on the other hand Cnt is less than the CAPACITY then the car park
is assumed to have spaces and subroutine DSPCS is called to display the
message SPCS. The ENTRY and EXIT switches are checked inside the
LOOP. When a vehicle enters the car park, ENTRY switch is activated and
program jumps to label LENTRY Similarly, when a vehicle leaves the car
park, EXIT switch is activated and program jumps to label LEXIT
Inside subroutine LENTRY, Cnt is incremented by 1 and LOCK is set to
1 if Cnt is greater than or equal to the CAPACITY. The program then
jumps to label BEGIN to repeat the process. Inside the LEXIT subrou-
tine, Cnt is decremented By 1 and LOCK is cleared. The program then
jumps to label BEGIN to repeat the process. Data bits are sent out using
the SHIFTOUT command of PicBasic Pro.
CAR PARK CONTROL SYSTEM
In this project a B08M04 type 4-digit 7-segment LED display is used.
Two switches are connected to the microcontroller inputs: ENTRY switch
and EXIT switch. These switches are operated by the barriers at the
entrance and the exit of the car park. The switches are normally at logic
1 and they go to logic when a barrier is lifted up.
Assume that a barrier lifts up automatically when a vehicle approaches
a barrier. The ENTRY barrier also has a locking mechanism and is
used to lock the barrier when the car park is full. Assume that the lock
is activated when a logic 1 is sent to it.
Assume that the capacity of the car park is 100. If the number of vehicles
inside the car park is less than 100 the the message SPCS (i.e. spaces)
is displayed. If the car park is full (i.e. there are 100 cars inside the car
park), then the message FULL is displayed.
Figure 5.87 (Continued)
PicBasic and PicBasic Pro projects 257
The display digits are organised as follows:
D4 D3 D2 Dl
Data is sent: Dl first, then D2, then D3 and finally D4
A PIC16F627 type microcontroller is used in the project with 4MHz
internal clock and internal reset.
The connection between the display and the microcontroller is as follows:
(display CE pin is connected to ground permanently)
RB6 Display DATA
RB7 Display CLOCK
The switches are connected as follows:
RBO ENTRY
RBI EXIT
RB2 LOCK
Author: Dogan Ibrahim
Date: October, 2005
Compiler: PicBasic Pro
File: CAR_PRK2.BAS
Modifications
DEFINITIONS
I VAR Byte ' Loop counter variable
temp VAR Byte ' Temporary byte variable
T VAR Byte[4] ' Digit segment bit patterns
LED1 VAR Bit ' Display LED 1 data
LED2 VAR Bit ' Display LED 2 data
Cnt VAR Word ' Cnt is a word variable
Figure 5.87 (Continued)
258 PIC BASIC projects
Symbol DATA_PIN = PORTB.6
Symbol CLK_PIN = PORTB.7
Symbol PENTRY = PORTB.O
Symbol PEXIT = PORTB.l
Symbol LOCK = PORTB.2
Symbol CAPACITY = 100
' START OF MAIN PROGRAM
TRISB = 3
LED1 =
LED2 =
Cnt =
' Display Data is RB6
' Display CLOCK is RB7
' START button
' STOP button
' LOCK output
' Car park capacity is 100 vehicles
' RBO, RB 1 are inputs, others output
' LED 1 is to be off
' LED 2 is to be off
' Clear the car park count
BEGIN:
IF Cnt >= CAPACITY THEN
GOSUB DFULL
ELSE
GOSUB DSPCS
ENDIF
' Check if ENTRY barrier is lifted up
LOOP:
temp =
BUTTON PENTRY, 0, 255, 0, temp, 1, LENTRY
temp =
BUTTON PEXIT, 0, 255, 0, temp, 1, LEXIT
GOTO LOOP
' START button is pressed. Start the counting
' Goto LENTRY if ENTRY =
' Goto LEXIT if EXIT switch =
LENTRY:
Cnt = Cnt + 1
IF Cnt >= CAPACITY THEN LOCK = 1
GOTO BEGIN
' A vehicle entered the car park
' Lock the ENTRY barrier
LEXIT:
Cnt = Cnt - 1
LOCK =
Figure 5.87 (Continued)
' A vehicle left the car park
' Unlock the ENTRY barrier
PicBasic and PicBasic Pro projects 259
DFULL:
GOTO BEGIN
T[0] = $1C: T[l]
GOSUB DISPLAY
RETURN
= $1C: T[2] = $7C: T[3] = $8E
DSPCS:
T[0] = $B6: T[l]
GOSUB DISPLAY
RETURN
= $9C: T[2] = $CE: T[3] = $B6
' This subroutine displays the 4 byte data in array T[I]. T[0] is the
' first data sent to the display.
DISPLAY:
' Send START bit
DATA_PIN = 1
PULSOUT CLK_PIN, 1
' Data = 1
' Send a clock
' Display each digit. Digit 1 is sent first
FOR I = To 3
SHIFTOUT DATA_PIN, CLK_PIN, 1, [ T[I] ]
NEXT I
' Send LED1 and LED 2 bits
DATA_PIN = LED1
PULSOUT CLK_PIN,1
DATA_PIN = LED2
PULSOUT CLK_PIN,1
' Data = LED1
' Send clock
' Data = LED 2
' Send clock
' Send TERMINATOR bit
DATA_PIN =
PULSOUT CLK_PIN,1
RETURN
' Data =
' Send clock
END
Figure 5.87 PicBasic Pro program of Project 19
' End of program
260 PIC BASIC projects
Project 20
Project title:
Seconds counter with LCD display
Project description: In this project a seconds counter is used and the count is displayed on a
LCD display as follows:
CNT = nnn
Figure 5.88 shows the block diagram of the project. A PIC microcon-
troller is used with its outputs connected to a parallel LCD.
PIC
Microcontroller
LCD
Figure 5.88 Block diagram of Project 20
Hardware:
The circuit diagram of the project is shown in Figure 5.89. A PIC16F627
microcontroller is used in the project with a 4 MHz internal clock and the
internal master clear circuit enabled during programming of the chip. In
this project a 2 row LCD is used but any type LCD can be used as long as
it is compatible with the HD44780 chip. The LCD display is connected to
the microcontroller using the default connections described in Section
4.3, i.e. the following connections are made between the microcontroller
and the LCD display:
LCD
Microcontroller
D4
RAO
D5
RA1
D6
RA2
D7
RA3
E
RB3
RS
RA4
Notice that pin RA4 of the microcontroller is open-drain output and
should be connected to the +V supply with a 10 K resistor.
The project constructed on a breadboard is shown in Figure 5.90.
PicBasic and PicBasic Pro projects 26 1
9V
Battery
0.33 |jF=t
78L05
^
+5V
^0.01mF
14
Vdd
PIC
16F627
RAO
RA1
RA2
RA3
RB3
RA4
Vss
17
11
18
12
13
14
set brightness
[
5K
DB4
DB5
DB6
DB7
VDD VEE
LCD
ERS
VSS R/W
6 4
10K
X
+5V
X
Figure 5.89 Circuit diagram of Project 20
Figure 5.90 Project 20 constructed on a breadboard
Flow diagram:
The flow diagram of the project is given in Figure 5.91. At the beginning
of the program PORTA and PORTB directions are configured. The pro-
gram then waits for about 0.5 s for the LCD to initialise. Variable Cnt is
incremented every second and the result is displayed on the LCD in the
following format:
CNT = nnn
262 PIC BASIC projects
f BEGIN J
i'
Configure port
directions
v
Wait 0.5 second
■"■
Cnt =
v
Display Cnt on LCD
i
'
Increment Cnt
i
'
Wait 1 second
i
'
Figure 5.91 Flow diagram of Project 20
Software:
PicBasic Pro
Figure 5.92 shows the PicBasic Pro program listing of the project. At the
beginning of the program PORTA and PORTB are configured as outputs.
Register CMCO is set to 7 so that PORTA pins are configured as digital
I/O. Cnt is declared as a word variable and program waits 500 ms for the
initialisation of the LCD. The LCD is cleared and the cursor is set to the
home position using the $FE,1 and $FE,2 LCD commands, respectively.
Variable Cnt is then displayed on the LCD in decimal format using the
LCDOUT statement. The program waits for 1 s and the process is repeated
after Cnt is incremented by one.
LCD SECONDS COUNTER
In this project an LCD display is connected to a PIC16F627 microcontroller.
The microcontroller is configured to operate with a 4MHz internal clock.
Figure 5.92 (Continued)
PicBasic and PicBasic Pro projects 263
Variable Cnt is incremented by 1 every second and the result is displayed on
the LCD.
The connection between the LCD display and the microcontroller is as follows:
Display
Microcontroller pin
DB4
RAO
DB5
RA1
DB6
RA2
RB7
RA3
E
RB3
RS
RA4
A 10K resistor is used to pull-up pin RA4 of the microcontroller.
RW pin of the LCD is connected to ground. The brightness of the LCD is
controlled by connecting a 5K variable resistor to pin VEE of the display.
Author:
Dogan Ibrahim
Date:
November, 2005
Compiler:
PicBasic Pro
File:
LCD1.BAS
Modifications
' Cnt is a word variable
DEFINITIONS
Cnt VAR Word
START OF MAIN PROGRAM
CMCON = 7
TRISA =
TRISB =
PAUSE 500
Cnt =
LCDOUT$FE,l
Figure 5.92 (Continued)
' RA0-RA3 are digital I/O
' PORTA is output
' PORTB is output
' Wait 0.5 second to initialize LCD
' Clear Cnt to zero
' Clear LCD
264 PIC BASIC projects
RPT:
LCDOUT $FE,2 ' Home cursor
LCDOUT "CNT = ", DEC Cnt ' Display count
PAUSE 1000 ' Wait 1 second
Cnt = Cnt + 1 ' Increment Cnt
GOTO RPT ' Repeat
END ' End of program
Figure 5.92 PicBasic Pro program of Project 20
PicBasic
PicBasic language does not provide any instructions to drive an LCD
directly. It is however possible to develop low-level routines to initialise
and drive LCD displays. The details of these routines require a detailed
knowledge of the internal operations of the LCDs and are only described
here briefly.
The steps to initialise an LCD are given below. Here, we are assuming that
the LCD is connected to the microcontroller in the standard way as shown
in Figure 5.89.
• Wait 20 ms after power up
• DO 3 times
- Send 3 to LCD
- Wait 10 ms
- Toggle Enable line
• ENDDO
• Wait 10 ms
• Send 2 to LCD (LCD in 4-bit mode)
• Wait 1 ms
• Toggle Enable line
• Send $28 to LCD (4-bit, 2-lines, 5X7 font)
• Send $0C to LCD (display on, no cursor, no blink)
• Send $06 to LCD (LCD entry mode, no shift)
Figure 5.93 shows the PicBasic program listing of the project. The major-
ity of the code used is to initialise and drive the LCD. At the beginning of
the program the addresses of the SFR registers used in the program are
defined. Then, PORTA and PORTB ports are configured as outputs. The
program then jumps to subroutine INITLCD to initialise the LCD. The
initialisation is basically in three steps: resetting mode o/the LCD, func-
tion setting of the LCD, display on routine, and the entry mode. The LCD
can be operated in either 4-bit or 8-bit modes. Operating in 4-bit mode has
PicBasic and PicBasic Pro projects 265
the advantage that only 4 data lines and 2 control lines, i.e. a total of 6
lines are required to initialise and control the LCD. At the beginning of
the initialisation routine the program waits for 20 ms for the internal logic
of the LCD to be initialised. At this point the LCD is by default in 8-bit
mode. Then the resetting mode starts where a data byte 3 should be sent to
the LCD data lines with a delay between each data output, and the Enable
line of the LCD should be toggled after each output. The recommended
delay is at least 4.1 ms after the first output and at least 100 |xs after the
other two outputs. In this example, a 10 ms delay is used after each output
and the PULSOUT statement is used to toggle the Enable line (bit 3 of
PORTB - RB3) of the LCD.
LCD is then in function setting mode where the LCD is put into the 4-bit
mode and the character font is selected. In the display on mode the display
and the cursor are turned on. The final stage of the initialisation is the
entry mode where the cursor movement mode and cursor blinking are
specified.
Subroutine LCDDATA can be used to display the character in register B2
on the current cursor position. The high nibble is first obtained by shift-
ing the data right by 4 bits. This nibble is sent to the LCD and the Enable
line is toggled. The low nibble is then sent to the LCD. LCD pin RS is set
to logic 1 during the data mode.
Subroutine SENDCOM is used to send a command to the LCD. LCD pin
RS is cleared to logic during the command mode. The command in regis-
ter B2 is sent to the LCD. The Enable line is toggled after sending each
nibble of the command.
Subroutine CLRLCD is used to clear the LCD display. Similarly, subrou-
tine HOMELCD can be used to set the cursor to the home position. Other
LCD commands (e.g. to move the cursor left or right, to move to the second
line, etc.) can easily be added to the program.
Variable Cnt is declared as a word and initialised to zero. The FOR loop
after label RPT uses statement LOOKUP to extract the characters of the
string to be displayed ("CNT=" in this case) where the characters are
stored in register B2 and then displayed by calling subroutine LCDDATA.
The 100 s, 10 s, and 1 s digits of variable Cnt are then extracted and stored
in registers B4, B5, and B6, respectively. For example, if Cnt = 573, then
B4 = 5, B5 = 7, and B6 = 3. Leading zeroes are suppressed by not dis-
playing them. The extracted numbers are then converted into ASCII by
adding 48 (ASCII "0") to each digit. The digits are assigned to register B2
266 PIC BASIC projects
and displayed on the LCD by calling subroutine LCDDATA. The maximum
value of Cut that can be displayed is 999 (this value can be increased by
extracting the 1000s digit of Cnt).
The program then waits for 1 s, variable Cnt is incremented by one and the
program repeats.
LCD SECONDS COUNTER
In this project an LCD display is connected to a PIC16F627 microcontroller.
The microcontroller is configured to operate with a 4MHz internal clock.
Variable Cnt is incremented by 1 every second and the result is displayed on
the LCD.
The connection between the LCD display and the microcontroller is as follows:
Display
Microcontroller pin
DB4
RAO
DB5
RA1
DB6
RA2
RB7
RA3
E
RB3
RS
RA4
A 10K resistor is used to pull-up pin RA4 of the microcontroller.
RW pin of the LCD is connected to ground. The brightness of the LCD is
controlled by connecting a 5K variable resistor to pin VEE of the display.
LCD is initialized and controlled by using low-level LCD routines.
Author: Dogan Ibrahim
Date: November, 2005
Compiler: PicBasic
File: LCD2.BAS
Figure 5.93 (Continued)
PicBasic and PicBasic Pro projects 267
Modifications
DEFINITIONS
Symbol PORTA = 5
Symbol TRISA = $85
Symbol PORTB = 6
Symbol CMCON = $ IF
Symbol TRISB = $86
Symbol Cnt = WO
' PORTA address
' TRISA address
' PORTB address
' CMCON address
' PORTB address
' Cnt is a word variable
' START OF MAIN PROGRAM
POKE CMCON, 7
POKE TRISA,
POKE TRISB,
GOSUB INITLCD
Cnt =
GOSUB CLRLCD
RPT:
GOSUB HOMELCD
' RA0-RA3 are digital I/O
' PORTA is output
' PORTB is output
' Initialize LCD
' Clear Cnt to zero
' Clear LCD
' Home cursor
FOR B4 = TO 3
LOOKUP B4, ("CNT = "), B2
GOSUB LCDDATA
NEXT B4
' Display CNT =
Find the 100s, 10s, and 10s digits and store in registers B4, B5, B6 respectively.
For example, if the number (Cnt) is 234, then B4 = 2, B5 = 3 and B6 = 4. Numbers
up to 999 can be displayed, i.e. maximum value of Cnt is 999. The program also blanks
zeroes from the beginning, e.g. if Cnt = 5, then only 5 is displayed, i.e.
005 is not displayed.
B4 = Cnt/100
B6 = Cnt//100
B5=B6/10
Figure 5.93 (Continued)
' B4 = leftmost digit
' B5 = middle digit
268 PIC BASIC projects
B6 = B6//10
IFB4 = OTHENN01
B2 = B4 + 48
GOSUB LCDDATA
CONT:
B2 = B5 + 48
GOSUB LCDDATA
B2 = B6 + 48
GOSUB LCDDATA
GOTO NXT
NOl:
IFB5 = 0THENNO2
GOTO CONT
N02:
B2 = B6 + 48
GOSUB LCDDATA
' B6 = rightmost digit
' Display top digit
' Display middle digit
' Display rightmost digit
' Wait 1 second, increment Cnt and repeat
NXT: PAUSE 1000
Cnt = Cnt +1
GOTO RPT
' Wait 1 second
' Increment Cnt
' Repeat
SUBROUTINES
This subroutine initializes the LCD
INITLCD:
PAUSE 20
FOR B2 = 1 TO 3
POKE PORTA, 3
PULSOUT 3, 100
PAUSE 10
NEXT B2
PAUSE 10
POKE PORTA, 2
PULSOUT 3, 100
B2 = $28
GOSUB SENDCOM
Figure 5.93 (Continued)
' Wait 20ms
' Do 3 times
' Toggle Enable line
' Wait 10ms
' Wait 10ms
' Send 2 to LCD
' Toggle Enable line
' Send $28 to LCD
PicBasic and PicBasic Pro projects 269
B2 = $0C ' Send $0C to LCD
GOSUB SENDCOM
B2 = $06 ' Send $06 to LCD
GOSUB SENDCOM
RETURN
' This subroutine clears the LCD
CLRLCD:
B2=l
GOSUB SENDCOM
PAUSE 2
RETURN
' This subroutine homes the cursor
HOMELCD:
B2 = 2
GOSUB SENDCOM
PAUSE 5
RETURN
' This subroutine sends data to the LCD. Data to be output is assumed to be
' in register B2.
LCDDATA:
B3 = B2 / 16 ' Shift B2 right 4 times
B3 = B3 + 16 ' Add the LCD RS bit
POKE PORTA, B3 ' Send to LCD
PULSOUT 3, 100 ' Toggle Enable line
B3 = B2 & $0F ' Extract 4 low order bits
B3 = B3 + 16 ' Add the LCD RS bit
POKE PORTA, B3 ' Send to LCD
PULSOUT 3, 100 ' Toggle Enable line
PAUSE 2 ' Wait 2ms to complete
RETURN
Figure 5.93 (Continued)
270 PIC BASIC projects
' This subroutine sends a command to the LCD. The comamnd is in B2.
' We have to shift top 4 bits down to the bottom 4 bits.
SENDCOM:
B3 = B2 / 16 ' Shift B2 right 4 times
B3 = B3 & $EF ' Clear RS =
POKE PORTA, B3 ' Send B3 to LCD
PULSOUT 3, 100 ' Toggle Enable line
B3 = B2 & $0F ' Get 4 low order bits
POKE PORTA, B3 ' Send B3 to LCD
PULSOUT 3, 100 ' Toggle Enable line
PAUSE 2 ' Wait 2ms to complete
POKE PORTA, $10 ' Set RS = 1
RETURN
END ' End of program
Figure 5.93 PicBasic program listing of Project 20
PicBasic and PicBasic Pro projects 27 1
Project 21
Project title:
Project description:
LCD-based clock with hours-minutes-seconds display
In this project an LCD-based digital clock is designed. Hours, minutes, and
seconds are displayed on the LCD in the following format:
HH:MM:SS
Two push-button switches are used to set the hours and minutes. Pressing the
hours button increments the hours between 00 and 23. Similarly, pressing the
minutes button increments the minutes between 00 and 59 so that the time
can be set.
Figure 5.94 shows the block diagram of the project.
Hours
Minutes
PIC
Microcontroller
HH:MM:SS
LOU
Figure 5.94 Block diagram of Project 2 1
Hardware:
The circuit diagram of the project is shown in Figure 5.95.
A PIC16F627 microcontroller is used in the project with a 4 MHz internal
clock and its master clear circuit is enabled during programming of the
chip. The LCD is connected in the default mode as described in project
20. Hours and minutes buttons are connected to RB0 and RBI pins of
PORTB, respectively.
The I/O connections are summarised below:
PORT pin
Mode
Connection
RAO
Output
LCDD4
RA1
Output
LCDD5
RA2
Output
LCDD6
RA3
Output
LCDD7
RB3
Output
LCDE
RA4
Output
LCDRS
RB0
Input
Hours button
RBI
Input
Minutes button
272 PIC BASIC Projects
1
r
9 V | 0.33 uF=b
Battery ,
78L05
t:
0.01 mf
10K
14
HOURS
K
16
MINUTES
^
+5VA
10K
O
ii
°i
Vdd
RBO
RAO
RA1
RA2
RA3
RB3
RA4
RB1
PIC
16F627
Vss
Figure 5.95 Circuit diagram of Project 21
17
18
11
12
13
14
set brightness
[
5K
DB4
DBS
DB6
DB7
VDD VEE
LCD
ER s vss R/w
6 4
10K
X
+5V
X
Flow diagram:
Software:
Notice that pin RA4 of the microcontroller is open-drain output and
should be connected to the + V supply with a 10K resistor.
The flow diagram of the project is given in Figure 5.96. The operation of
the project is based on a timer interrupt. The timer interrupt is set to gen-
erate an interrupt every second. Inside the ISR the time is advanced by 1 s
and the minutes and hours are adjusted if necessary and the hours, min-
utes, and seconds are displayed every second on the LCD.
In addition to displaying the time, the hours and minutes buttons can be
used to set the time at the beginning of a session. Pressing the hours but-
ton advances the hours display by 1 h. Similarly, pressing the minutes but-
ton advances the minutes display by 1 min.
PicBasic
The program in this project is based on the timer interrupt. PicBasic lan-
guage does not support interrupts from high-level language and therefore
only the PicBasic Pro program of this project is given.
PicBasic Pro
Figure 5.97 shows the PicBasic Pro program listing of the project. At the
beginning of the program Hrsjbutton and Minsjbutton are assigned to
RBO and RBI, respectively. The following variables are then declared:
Hour Stores the hours field of time
Minute Stores the minutes field of time
PicBasic and PicBasic Pro projects 273
BEGIN
ISR
Configure I/O ports
Configure timer
interrupt for 1 sec
interrupts
Display time
Hours button^
. Y
Increment hours
.pressed? ^
N
'
Figure 5.96 Flow diagram of Project 21
BEGIN
Increment
seconds count
Seconds =
Increment minutes
Minutes =
Increment hours
Set display flag
Re-enable
timer interrupt
RETURN
Second Stores the seconds field of time
Ticks This variable stores the tick number. It is incremented
by one whenever a timer interrupt occurs. A second
consists of 61 Ticks
Disp This variable controls writing to the LCD.
When Disp = 1 , the LCD is updated
Delay This variable is used in the delay loop of the contact
debouncing subroutine
Initially the Hour, Minute, Second, and Ticks are all cleared to zero. Timer
pre-scaler is set to 64 by loading the OPTION_REG to bit pattern
"00000101" (hexadecimal $05). Timer interrupt register TMR0 is then left
274 PIC BASIC Projects
to count from to 255 so that the timer interrupts occur at 16.384 ms inter-
vals (64 X 256 = 16.384 ms). Interrupt service routine starting address is
named as ISR and global and timer interrupts are enabled by setting the
INTCON register to bit pattern "10100000" (i.e. hexadecimal $A0).
Inside the main program the hours and minutes buttons are checked con-
tinuously so that the time can be set at the beginning of the program. If the
hour button is pressed, variable Hour is incremented by 1 . When Hour is
equal to 24 it is cleared to zero. Similarly, when the minute button is
pressed, variable Minute is incremented by 1 . When Minute reached to 60
it is cleared to zero.
The LCD is updated whenever any of the buttons are pressed or when the
seconds field is updated inside the ISR.
Subroutine Debounce is used to debounce the switch contacts. A 200 ms
delay is inserted after a button is pressed. This delay debounces the con-
tacts and also gives time to the user to set the time correctly. Notice that
the delay loop consists of a FOR loop which is repeated 200 times and the
actual delay is 1 ms inside the loop. The reason for doing it this way and
not using the PAUSE 200 statement is because we want the timer inter-
rupts to be accepted during the waiting period. If PAUSE 200 is used then
interrupts will not be checked for 200 ms and we may get wrong counts.
The interrupt service routine starts with label ISR. Inside this routine
variable Ticks is incremented by 1. When Ticks reaches 61 then it is
assumed that Is has elapsed (61 X 16.384ms = 999.424ms) and vari-
able Second is incremented by 1 . When Second reaches 60 it is cleared to
zero and Minute is incremented by 1 . Similarly, when Minute reaches 60
it is cleared to zero and Hour is incremented by 1 . At the end of the ISR
variable Disp is set to 1 if the time has been updated and timer interrupts
are re-enabled by clearing bit 2 of register INTCON.
Notice that the actual timer interrupt interval is 999.424 ms which is
576 ms short of a second. If we take into account the delay caused by the
operations inside the ISR our timer intervals are probably very close to 1 s
(it is not possible to calculate the exact delay when using a high-level lan-
guage since the exact execution times of the instructions are not known).
In this project the internal clock of the microcontroller is used as the clock
source. This clock is not accurate and for more accurate results, use of an
external crystal clock source is recommended.
PicBasic and PicBasic Pro projects 275
LCD BASED CLOCK
In this project an LCD display is connected to a PIC16F627 microcontroller.
The microcontroller is configured to operate with a 4MHz internal clock.
The project is a clock, showing the hours, minutes, and seconds in the
following format:
HH:MM:SS
The connection between the LCD display and the microcontroller is as follows:
Display
Microcontroller pin
DB4
RAO
DB5
RA1
DB6
RA2
RB7
RA3
E
RB3
RS
RA4
Hrs button
RBO
Mins button
RBI
Two push-button switches are connected to RBO and RB 1 pins of PORTB
in order to set the time (hours and minutes fileds of the time).
The hours button is connected to RBO and pressing this button increments
hours by 1 . When hours reaches 24, it is reset back to 0. Similarly, the
minutes button is connected to RB 1 and pressing this button increments
the minutes by 1. When minutes reached 60, it is reset back to 0.
The timer interrupt TMRO is used to update the time. The timer is configured
to interrupt at every 16.384ms. When the count is 61, one second is elapsed
and the seconds variable is incremented by 1 . The minutes or the hours
variables are incremented if necessary.
A 10K resistor is used to pull-up pin RA4 of the microcontroller.
RW pin of the LCD is connected to ground. The brightness of the LCD is
controlled by connecting a 5K variable resistor to pin VEE of the display.
Figure 5.97 (Continued)
276 PIC BASIC Projects
Author:
Dogan Ibrahim
Date:
November, 2005
Compiler:
PicBasic Pro
File:
LCD3.BAS
Modifications
DEFINITIONS
Symbol Hrs_button = PORTB.O
Symbol Mins_button = PORTB.l
Ticks
VAR
byte
Hour
VAR
byte
Minute
VAR
byte
Second VAR
byte
Disp
VAR
byte
Delay
VAR
byte
TRISA
=
TRISB
= 3
CMCON = 7
PAUSE 500
' Hour setting button
' Minute setting button
' Tick count (61 ticks = 1 sec)
' Hour variable
' Minute variable
' Second variable
' Disp = 1 to update display
' Used to Debounce button
' PORTA is output
'RB0,RB1 are inputs
' PORTA digital I/O
' Wait 0.5 sec for LCD to initialize
' Clear Hour, Minute, Second and Ticks to zero
Hour =
Minute =
Second =
Ticks =
' Initialize timer interrupt. The prescaler is set to 64 and the
' TMR0 is left to run from to 255. With a clock frequency of 4MHz,
' The timer interrupt is generated at every 256 * 64 = 16.384ms.
Figure 5.97 (Continued)
PicBasic and PicBasic Pro projects 277
' Inside the ISR, variable ticks is incremented by 1. When Ticks = 61
' then time for a timer interrupt is: 61*16.384 = 999.424ms and variable
' Second is then updated, i.e. Second is updated nearly every second.
OPTION_REG = $05 ' Set prescaler = 64
ON INTERRUPT GOTO ISR ' ISR routine
INTCON = $A0 ' Enable TMRO interrupt and global interrupts
LCDOUT $FE, 1 ' Clear LCD
' Beginning of MAIN program loop
LOOP:
.
' Check Hour button and if pressed increment variable Hour
IF Hrs_button = THEN
Hour = Hour + 1
IF Hour = 24 THEN Hour =
Gosub Debounce
ENDIF
' Check Minute button and if pressed increment variable Minute
IF Mins_button = THEN
Minute = Minute +1
IF Minute = 60 THEN Minute =
Gosub Debounce
ENDIF
Display update section. The display is updated when variable
Disp is 1 . This variable is set to 1 inside the ISR when the
seconds changes. The cursor is set to home position and the
time is displayed on the LCD
IF Disp = 1 THEN
LCDOUT $FE, 2
LCDOUT DEC2 Hour, ":",DEC2 Minute, ":",DEC2 Second
Disp =
ENDIF
GOTO LOOP
Figure 5.97 (Continued)
278 PIC BASIC Projects
This subroutine Debounces the buttons. Also, a delay is introduced when
a button is pressed so that the variable attached to the button (Hour or Second)
can be incremented after a small delay.
Debounce:
FOR Delay = 1 To 200
Pause 1
NEXT Delay
Disp = 1
RETURN
' Delay 1ms inside a loop. This way,
' timer interrupts are not stopped
' Set display flag to 1
This is the Timer interrupt Service Routine. The program jumps to this code
whenever the timer overflows from 255 to 0. i.e. every 256 count. The prescaler
is set to 64 and the clock frequency is 4MHz. i.e. the basic instruction cycle
time is 1 microsecond. Thus, timer interrupts occur at every 64*256 = 16.384ms.
Variable Ticks is incremented by 1 each time a timer interrupt occurs. When Ticks
is equal to 61, then one second has elapsed (16.384*61 = 999.424ms) and then
variable Second is incremented by 1 . When Second is 60, variable Minute is
incremented by 1 . When Minute is 60, variable Hour is incremented by 1 .
Timer TMR0 interrupts are re-enabled just before the program exits this routine.
DISABLE
ISR:
Ticks = Ticks + 1
IF Ticks < 61 THENNoUpdate
' 1 second has elapsed, now update seconds and if necessary minutes and hours.
Figure 5.97 (Continued)
PicBasic and PicBasic Pro projects 279
Ticks =
Second = Second + 1
IF Second = 60 THEN
Second =
Minute = Minute + 1
IF Minute = 60 THEN
Minute =
Hour = Hour + 1
IF Hour = 24 THEN
Hour =
ENDIF
ENDIF
ENDIF
Disp = 1
' End of time update
' Update second
' Update Minute
' Update Hour
' Set to update display
NoUpdate:
INTCON.2 =
Resume
ENABLE
' Re-enable TMRO interrupts
' Re-enable interrupts
END
END
Figure 5.97 PicBasic Pro program of Project 21
' End of program
280 PIC BASIC Projects
Project 22
Project title:
Project description:
LCD-based chronometer
In this project an LCD-based chronometer is designed. The chronometer
counts the elapsed time in seconds and displays in hours, minutes, and
seconds in the following format:
HH:MM:SS
Three push-button switches are used to start, stop, and clear the chronom-
eter. Pressing button START starts the chronometer which counts in sec-
onds. Pressing button STOP stops the counting. Pressing button CLEAR
clears the display so that the chronometer is ready for the next count.
Figure 5.98 shows the block diagram of the project.
START
STOP
CLEAR
PIC
Microcontroller
HH:MM:SS
LOU
Figure 5.98 Block diagram of Project 22
Hardware:
The circuit diagram of the project is shown in Figure 5.99.
A PIC16F627 microcontroller is used in the project with a 4 MHz internal
clock. The LCD is connected in the default mode as described in project
21. START, STOP, and CLEAR buttons are connected to RBO, RBI, and
RB2 pins of PORTB, respectively.
The I/O connections are summarised below:
PORT pin
Mode
Connection
RAO
Output
LCDD4
RA1
Output
LCDD5
RA2
Output
LCDD6
RA3
Output
LCDD7
RB3
Output
LCDE
RA4
Output
LCDRS
RBO
Input
START button
RBI
Input
STOP button
RB2
Input
CLEAR button
PicBasic and PicBasic Pro projects 28 1
9V
Battery
0.33 pF=b
78L05
X
+5V
— 1—0.01 pF
START
^
10K
14
°i
STOP
^
+5VA
10K
CLEAR
W
%
+5VA
10K
O
h
1
Vdd
RBO
RAO
RA1
RA2
RA3
RB3
RA4
RB1
PIC
16F627
Vss
RB2
Figure 5.99 Circuit diagram of Project 22
17
11
18
12
13
14
set brightness
— r=n—
5K
DB4
DBS
DB6
DB7
VDD VEE
LCD
ERS
VSS R/W
6 4
10K
X
+5V
X
Notice that pin RA4 of the microcontroller is open-drain output and
should be connected to the + V supply with a 10K resistor.
Flow diagram:
The flow diagram of the project is given in Figure 5. 100. The operation of
the project is based on a timer interrupt. The timer interrupt is set to gen-
erate an interrupt every second when the chronometer is started. Pressing
the START button clears the timer register TMR0 and enables interrupts.
Pressing STOP button disables interrupts so that the final count can be
displayed and viewed on the LCD. Pressing the CLEAR button clears the
hours, minutes, seconds, and ticks so that a new count can start.
Software:
PicBasic
The program in this project is based on the timer interrupt. PicBasic lan-
guage does not support interrupts from high-level language and therefore
only the PicBasic Pro program of this project is given.
PicBasic Pro
Figure 5.101 shows the PicBasic Pro program listing of the project. At the
beginning of the program START _button, STOP_button, and CLEARJbutton
282 PIC BASIC Projects
BEGIN
Configure I/O ports
Configure timer
interrupt for 1 sec
interrupts
Display HH:MM:SS
TMRO =
Enable interrupts
Stop interrupts
CLEAR buttorT
pressed ?
N v
Clear Hour, Minute,
Second, Ticks
Figure 5.100 Flow diagram of Project 22
ISR
BEGIN
Increment
seconds count
Seconds =
Increment minutes
Minutes =
Increment hours
Set display flag
Re-enable
timer interrupt
RETURN
are assigned to RBO, RBI, and RB2, respectively. The following variables
are then declared:
Hour
Minute
Second
Ticks
Disp
Stores the hours field of time
Stores the minutes field of time
Stores the seconds field of time
This variable stores the tick number. It is incremented
by one whenever a timer interrupt occurs. A second
consists of 6 1 Ticks
This variable controls writing to the LCD When
Disp = 1, the LCD is updated
PicBasic and PicBasic Pro projects 283
Initially the Hour, Minute, Second, and Ticks are all cleared to zero. Timer
pre-scaler is set to 64 by loading the OPTION_REG to bit pattern
"00000101" (hexadecimal $05). Timer interrupt register TMR0 is then
left to count from to 255 so that the timer interrupts occur at 16.384 ms
intervals (64 X 256 = 16.384 ms).
When the START button is pressed, timer register TMR0 is reset to zero
and timer interrupts are enabled. Thus, an interrupt is generated every
second and the display shows the elapsed time in HH:MM:SS. When the
STOP button is pressed timer interrupts are disabled and the final count is
displayed on the LCD. Pressing the CLEAR button clears the time vari-
ables so that the chronometer is ready for the next count.
The interrupt service routine starts with label ISR. Inside this routine
variable Ticks is incremented by 1. When Ticks reaches 61 then it is
assumed that Is has elapsed (61 X 16.384ms = 999.424ms) and vari-
able Second is incremented by 1. When Second reaches 60 it is cleared to
zero and Minute is incremented by 1 . Similarly, when Minute reaches 60
it is cleared to zero and Hour is incremented by 1 . At the end of the ISR
variable Disp is set to 1 if the time has been updated and timer interrupts
are re-enabled by clearing bit 2 of register INTCON.
Notice that the actual timer interrupt interval is 999.424 ms which is
576 ms short of a second. If we take into account the delay caused by the
operations inside the ISR our timer intervals are probably very close to 1 s
(it is not possible to calculate the exact delay when using a high-level lan-
guage since the exact execution times of the instructions are not known).
In this project the internal clock of the microcontroller is used as the clock
source. The internal clock is not accurate and for more accurate results,
use of an external crystal clock source is recommended.
LCD BASED CHRONOMETER
In this project an LCD display is connected to a PIC16F627 microcontroller.
The microcontroller is configured to operate with a 4MHz internal clock. For
more accurate results, an external crystal clock source should be used.
The project is a chronometer, counting in seconds and displaying the hours,
minutes, and seconds in the following format:
HH:MM:SS
Figure 5.101 (Continued)
284 PIC BASIC Projects
The connection between the LCD display and the microcontroller is as follows:
Display
Microcontroller pin
DB4
RAO
DB5
RA1
DB6
RA2
RB7
RA3
E
RB3
RS
RA4
START button
RBO
STOP button
RBI
CLEAR button
RB2
Three push-button switches are connected to RBO, RBI and RB2 pins of
PORTB. Pressing START starts the chronometer counting in seconds. Pressing
STOP button stops the chronometer and displays the elapsed time in HH:MM:SS
format. Pressing the CLEAR button clears the chronometer so that it is ready for
the next count.
The timer interrupt TMRO is used to update the time. The timer is configured
to interrupt at every 16.384ms. When the count is 61, one second is elapsed
and the seconds variable is incremented by 1 . The minutes or the hours
variables are incremented if necessary.
A 10K resistor is used to pull-up pin RA4 of the microcontroller.
RW pin of the LCD is connected to ground. The brightness of the LCD is
controlled by connecting a 5K variable resistor to pin VEE of the display.
Author:
Dogan Ibrahim
Date:
November, 2005
Compiler:
PicBasic Pro
File:
LCD4.BAS
Modifications
Figure 5.101 (Continued)
PicBasic and PicBasic Pro projects 285
' DEFINITIONS
Symbol START_button = PORTB.O
Symbol STOP_button = PORTB.l
Symbol CLEAR_button = PORTB.2
' START button
' STOP button
' CLEAR button
Ticks
VAR byte
Hour
VAR byte
Minute
VAR byte
Second
VAR byte
Disp
VAR byte
Delay
VAR byte
TRISA =
TRISB = 7
CMCON = 7
PAUSE 500
' Tick count (6 1 ticks = 1 sec)
' Hour variable
' Minute variable
' Second variable
' Disp = 1 to update display
' Used to Debounce button
' PORTA is output
' RB0,RB1,RB2 are inputs
' PORTA digital I/O
' Wait 0.5 sec for LCD to initialize
' Clear Hour, Minute, Second and Ticks to zero
Hour =
Minute =
Second =
Ticks =
Disp = 1
Clear hours
Clear minutes
Clear seconds
Clear ticks
Force to display 00:00:00 at startup
Initialize timer interrupt. The prescaler is set to 64 and the
TMR0 is left to run from to 255. With a clock frequency of 4MHz,
The timer interrupt is generated at every 256 * 64 = 16.384ms.
Inside the ISR, variable ticks is incremented by 1 . When Ticks = 61
then time for a timer interrupt is: 61*16.384 = 999.424ms and variable
Second is then updated, i.e. Second is updated nearly every second.
OPTION_REG = $05
ON INTERRUPT GOTO ISR
LCDOUT $FE, 1
' Set prescaler = 64
' ISR routine
' Clear LCD
' Beginning of MAIN program loop
Figure 5.101 (Continued)
286 PIC BASIC Projects
LOOP:
' Check if START button is pressed and enable timer interrupts so that
' counting starts if this button is pressed
IF START_button = THEN
TMRO = ' Initialize TMRO register
INTCON = $A0 ' Enable timer interrupt
Disp = 1 ' Enable display
ENDIF
' Check if STOP button is pressed and disable timer interrupt so that
' counting stops and displays the elapsed time in HH:MM:SS format
IF STOP_button = THEN
INTCON = ' Disable timer interrupt
Disp = 1 ' Enable display
ENDIF
' Check if CLEAR button is pressed and clear the display and time variables
' so that a new count can start.
IF CLEAR_button = THEN
Hour =
Minute =
Second =
Ticks =
Disp = 1
ENDIF
Display update section. The display is updated when variable Disp = 1 .
This variable is set to 1 inside the ISR when the seconds changes.
The cursor is set to home position and the time is displayed on the LCD.
IF Disp = 1 THEN
LCDOUT $FE, 2
LCDOUT DEC2 Hour, ":",DEC2 Minute, ":",DEC2 Second
Disp =
ENDIF
GOTO LOOP
' This is the Timer interrupt Service Routine. The program jumps to this code
Figure 5.101 (Continued)
PicBasic and PicBasic Pro projects 287
' whenever the timer overflows from 255 to 0. i.e. every 256 count. The prescaler
' is set to 64 and the clock frequency is 4MHz. i.e. the basic instruction cycle
' time is 1 microsecond. Thus, timer interrupts occur at every 64*256 = 16.384ms.
' Variable Ticks is incremented by 1 each time a timer interrupt occurs. When Ticks
' is equal to 61, then one second has elapsed (16.384*61 = 999.424ms) and then
' variable Second is incremented by 1. When Second is 60, variable Minute is
' incremented by 1. When Minute is 60, variable Hour is incremented by 1.
' Timer TMRO interrupts are re-enabled just before the program exits this routine.
DISABLE
ISR:
Ticks = Ticks + 1
IF Ticks < 61 THEN NoUpdate
' 1 second has elapsed, now update seconds and if necessary minutes and hours.
Ticks =
Second = Second + 1
IF Second = 60 THEN
Second =
Minute = Minute + 1
IF Minute = 60 THEN
Minute =
Hour = Hour + 1
IF Hour = 24 THEN
Hour =
ENDIF
ENDIF
ENDIF
Disp = 1 ' Set to update display
' End of time update
NoUpdate:
INTCON.2 = ' Re-enable TMRO interrupts
Resume
ENABLE ' Re-enable interrupts
END
END ' End of program
Figure 5.101 PicBasic Pro program of Project 22
288 PIC BASIC Projects
Project 23
Project title:
LCD-based voltmeter using A/D converter
Project description: In this project an LCD-based voltmeter is designed. The project can be
used to measure and display analog voltages to up to +5 V. The voltage is
displayed in millivolts in the following format:
V = nnnn
where nnnn is the measured voltage. Figure 5.102 shows the block dia-
gram of the project where the voltage to be measured is applied to one of
the analog-to-digital converter (A/D) channels of a PIC microcontroller
having built-in A/D converters.
Voltage to be
measured
(Oto +5V)
Figure 5.102 Block diagram of Project 23
PIC
Microcontroller
V = nnnn
LCD
Hardware:
The circuit diagram of the project is shown in Figure 5. 103. In this project
a PIC16F73-type microcontroller is used. This is a 28-pin microcontroller
with built-in 5 channel A/D converters, each having 8-bits of resolution.
Other PIC microcontrollers such as PIC16F630 or PIC16F877, or others
with built-in A/D converters can easily be used in this project.
PIC16F73 is a 28-pin microcontroller with the following features:
8 K flash program memory
368 bytes RAM memory
Up to 20 MHz operation
3 timer circuits
Analog capture, compare and PWM circuits
8-bit 5 channel A/D converter
Built-in USART
SPI and I 2 C bus compatibility.
In this project, the microcontroller is operated from a 4 MHz resonator
and the voltage to be measured is applied to analog input ANO of the
PicBasic and PicBasic Pro projects 289
microcontroller. The analog channels are named ANO to AN4 and they
correspond to the following PORTA names:
Pin
Channel
RAO
ANO
RA1
AN1
RA2
AN2
RA3
AN3
RA4
AN4
The default LCD connections also use pins RAO to RA4. In order to
reserve pins RAO to RA4 for analog channels, the LCD is connected to
PORTB as shown below.
PORTB
LCD pin
RBO
D4
RBI
D5
RB2
D6
RB3
D7
RB4
E
RB5
RS
9V
Battery
0.33 pFd=
78L05
t:
+5V
-7-0.01MF
4.7K
Voltage to be
Measured
20
Vdd
MCLR
RBO
RB1
RB2
RB3
RB4
RB5
ANO
PIC
16F73
Vss
OSC1
Vss
OSC2
X
21
22
23
24
25
26
19
10
11
12
13
14
set brightness
c=D—
5K
DB4
DB5
DB6
DB7
VDD
VEE
LCD
ERS
6 4
4 MHz resonator
VSS R/W
X
Figure 5.103 Circuit diagram of Project 23
290 PIC BASIC Projects
Flow diagram:
Software:
The new LCD connection is defined using a set of DEFINE statements as
described in the programming section. The operation of the project is sim-
ple: Analog voltage is sampled every second and converted into digital
form. The voltage is then scaled and displayed on the LCD.
The flow diagram of the project is given in Figure 5.104. At the beginning of
the program, LCD connections, port directions, and the AID converter are
configured. The voltage to be measured is then converted into digital form,
scaled and displayed on the LCD. After 1 s delay this process is repeated.
PicBasic
The PicBasic program of this project is complex since LCDs are not sup-
ported directly and the LCD routines developed in Project 20 use the
default LCD connections. Only the PicBasic Pro program listing of this
project is given.
N
BEGIN
Configure LCD
connections
Configure port
directions
Configure A/D
converter
Start conversion
Convert to mV
Display result on
the LCD
Wait 1 second
Figure 5.104 Flow diagram of Project 23
PicBasic and PicBasic Pro projects 29 1
PicBasic Pro
The PicBasic Pro program listing of the project is given in Figure 5.105.
At the beginning of the program a set of DEFINE statements are used to
define the connections between the LCD and the microcontroller.
Variable Res stores the converted digital data. Variable Volts stores the result
of conversion in millivolts. In order to convert the measured voltage to mil-
livolts, it is necessary to multiply the result of the conversion with 19.53 (256
steps correspond to 5000 mV, thus, each step is 5000mV/256 = 19.53 mV).
But since the PicBasic Pro language does not support floating point
arithmetic, an approximation is made here and the result is multiplied
with 19 only.
The steps for an A/D conversion using the PIC16F73 microcontroller are
as follows (assuming that the A/D conversion interrupt is not used):
• Configure the A/D module
- Configure analog pins, reference voltage, and digital I/O (register
ADCON1)
- Select A/D conversion clock (register ADCON0)
- Turn on A/D module (register ADCON0)
• Select an A/D input channel
• Start A/D conversion
- Set GO/DONE bit of register ADCON0
• Wait for the conversion to complete
- Wait until GO/DONE bit of register ADCON0 is cleared
• Read the A/D result register (ADRES)
• Go to step 2 or 3 for next conversion.
In Figure 5. 105, register ADCON1 is initially cleared so that AN0 to AN4
are analog inputs and the A/D converter reference is the supply voltage,
VDD. Register ADCON0 is then set to bit pattern "11000001" to select
the internal RC oscillator as the source of clock for the A/D. Analog chan-
nel AN0 is also selected and the A/D module is turned on.
A/D conversion is started by setting the GO/DONE bit of register
ADCON0, i.e. ADCON0.2 = 1. The program then waits until the conver-
sion is complete which is indicated by the GO/DONE bit going to logic 0,
i.e. ADCON0.2 = 0. The result of the conversion is then read from regis-
ter ADRES and is stored as a digital value between and 255 in variable
Res. Res is multiplied with 19 (it should be 19.53 for an exact result) and
stored in variable Volts. Volts stores the measured voltage in millivolts.
This voltage is then displayed on the LCD as a 4-digit decimal number.
The program repeats after a one-second delay.
292 PIC BASIC Projects
LCD BASED VOLTMETER
In this project an LCD display is connected to a PIC16F73 microcontroller.
The microcontroller is configured to operate with a 4MHz external resonator.
The project is a voltmeter, which can measure the voltage applied to the analog
input ANO. The voltage to be measured must be between V and +5V.
The connection between the LCD display and the microcontroller is as follows:
Display
Microcontroller pin
DB4
RBO
DB5
RBI
DB6
RB2
RB7
RB3
E
RB4
RS
RB5
Analog input ANO (RAO)
RW pin of the LCD is connected to ground. The brightness of the LCD is
controlled by connecting a 5K variable resistor to pin VEE of the display.
The PIC16F73 microcontroller has built in 8-bit 5 channel A/D converters.
The A/D reference voltage is set to +5V. With 8-bit converters, operating with
a reference voltage of +5V, the bit resolution is 5000/256 = 19.53mV
The result is displayed in mV in the following format:
v =
nnnn
Author:
Dogan Ibrahim
Date:
November, 2005
Compiler:
PicBasic Pro
File:
LCD5.BAS
Modifications
Figure 5.105 (Continued)
PicBasic and PicBasic Pro projects 293
DEFINITIONS
Define LCD connections
DEFINE LCD_DREG PORTB
DEFINE LCD_DBIT
DEFINE LCD_RSREG PORTB
DEFINE LCD_RSBIT 5
DEFINE LCD_EREG PORTB
DEFINE LCD_EBIT 4
DEFINE LCD_BITS 4
DEFINE LCD_LINES 2
Res Var Word
Volts Var Word
Conv Con 19
TRISA = 1
TRISB =
PAUSE 500
' Initialize the A/D converter
ADCON1 =
ADCONO = %1 1000001
LCDOUT $FE, 1
AGAIN:
' Start A/D conversion
ADCON0.2 = 1
' Wait until conversion is complete
WT: PAUSE 1
IF ADCON0.2 = 1 THEN WT
Res = ADRES
Volts = Res * Conv
Figure 5.105 (Continued)
' LCD Data bits on PORTB
' PORTB starting address
' LCD RS bit on PORTB
' LCD RS bit address
' LCD E bit on PORTB
' LCD E bit address
' LCD in 4-bit mode
' LCD has 2 rows
' A/D converter result
' Result of conversion in mV
'5000/256 =19.53, take 19
' RAO (AN0) is input
' PORTB is output
' Wait 0.5sec for LCD to initialize
' Make AN0 to AN4 as analog inputs,
' make reference voltage = VDD
' A/D clock is internal RC, select AN0
' Turn on A/D converter
' Clear LCD
' Get result of conversion
' Result in mV
294 PIC BASIC Projects
LCDOUT $FE,2,"V = ",DEC4 Volts ' Display result
PAUSE 1000 ' Wait 1 second
GOTO AGAIN ' Repeat
END ' End of program
Figure 5.105 PicBasic Pro listing of Project 23
The displayed voltage by the program in Figure 5.105 is not accurate
since the converted signal is multiplied by 19 and not by 19.53. The rea-
son for this was because the PicBasic Pro language does not support float-
ing point arithmetic. The result could however be made more accurate by
performing the multiplication with 19.53 as follows:
• Consider 19.53 as 19 + 0.53
• Read the A/D result into variable Res
• Multiply Res with 19 and store in Volts 1
• Multiply Res with 53 and store in Volts!
• Divide Volts! to VoltslOO
• Add Volts! to Volts 1. Volts 1 now contains a number which is more
closely related to Res* 19. 53
The program given in Figure 5.106 implements the changes described
above. In this program variable Volts 1 stores the measured voltage in milli-
volts and this variable is displayed as a 4 digit decimal number.
LCD BASED VOLTMETER
In this project an LCD display is connected to a PIC16F73 microcontroller.
The microcontroller is configured to operate with a 4MHz external resonator.
The project is a voltmeter, which can measure the voltage applied to the analog
input AN0. The voltage to be measured must be between V and +5 V
The connection between the LCD display and the microcontroller is as follows:
Display Microcontroller pin
DB4 RB0
Figure 5.106 (Continued)
PicBasic and PicBasic Pro projects 295
DB5
RBI
DB6
RB2
RB7
RB3
E
RB4
RS
RB5
Analog input ANO (RAO)
RW pin of the LCD is connected to ground. The brightness of the LCD is
controlled by connecting a 5K variable resistor to pin VEE of the display.
The PIC16F73 microcontrolelr has built in 8-bit 5 channel A/D converters.
The A/D reference voltage is set to +5 V. With 8-bit converters, operating with
a reference voltage of +5 V, the bit resolution is 5000/256 = 19.53 mV.
The result is displayed in mV in the following format:
V = nnnn
This program is similar to LCD5.BAS, but here the result is more accurate since
the conversion factor is taken as 19.53 and not just 19.
Author:
Dogan Ibrahim
Date:
November, 2005
Compiler:
PicBasic Pro
File:
LCD5-1.BAS
Modifications
DEFINITIONS
Define LCD connections
DEFINE LCD_DREG PORTB
DEFINE LCD_DBIT
DEFINE LCD_RSREG PORTB
DEFINE LCD_RSBIT 5
DEFINE LCD_EREG PORTB
DEFINE LCD EBIT 4
' LCD Data bits on PORTB
' PORTB starting address
' LCD RS bit on PORTB
' LCD RS bit address
' LCD E bit on PORTB
' LCD E bit address
Figure 5.106 (Continued)
296 PIC BASIC Projects
DEFINE LCD_BITS 4
DEFINE LCD_LINES 2
Res Var Word
Volts 1 Var Word
Volts2 Var Word
Convl Con 19
Conv2 Con 53
TRISA = 1
TRISB =
PAUSE 500
' Initialize the A/D converter
ADCON1=0
ADCON0 = %l 1000001
LCDOUT $FE, 1
AGAIN:
c
' Start A/D conversion
ADCON0.2 = 1
' Wait until conversion is complete
WT: PAUSE 1
IF ADCON0.2 = 1 THEN WT
Res = ADRES
Volts 1 =Res * Convl
Volts2 = Res * Conv2
Volts2 = Volts2 / 100
Volts 1 = Volts 1 + Volts2
LCDOUT $FE,2,"V = ",DEC4 Volts 1
PAUSE 1000
GOTO AGAIN
END
' LCD in 4-bit mode
' LCD has 2 rows
' A/D converter result
' First part of result in mV
' Second part of result in mV
' 5000/256 = 19.53, this is the decimal part
' This is the fractional part
' RAO (AN0) is input
' PORTB is output
' Wait 0.5 sec for LCD to initialize
' Make AN0 to AN4 as analog inputs,
' make reference voltage = VDD
' A/D clock is internal RC, select AN0
' Turn on A/D converter
' Clear LCD
' Get result of conversion
' Multiply by 19
' Multiply by 53
' Result in mV
' Display result
' Wait 1 second
' Repeat
' End of program
Figure 5.106 More accurate PicBasic Pro program
PicBasic and PicBasic Pro projects 297
PicBasic Pro language provides a high-level instruction called ADCIN for
starting an A/D conversion and reading the result of the conversion. The
format of this instruction is
ADCIN channel, var
Where channel is the A/D channel used, and var is the variable which is
to store the result of the conversion. Using this instruction, simplifies the
programming of an A/D converter channel. Figure 5.107 gives the pro-
gram listing which makes use of the ADCIN instruction.
Notice that the width of the A/D is defined with ADC_BITS, the A/D clock
is defined with ADC_CLOCK (3 corresponds to the internal RC clock), and
the A/D sampling time is defined with ADC_SAMPLEUS. Although we are
using the ADCIN statement to read the analog input, we still have to config-
ure the ADCON0 and ADCON1 registers before starting a conversion.
LCD BASED VOLTMETER
In this project an LCD display is connected to a PIC16F73 microcontroller.
The microcontroller is configured to operate with a 4MHz external resonator.
The project is a voltmeter, which can measure the voltage applied to the analog
input ANO. The voltage to be measured must be between 0V and +5 V
The connection between the LCD display and the microcontroller is as follows:
Display
Microcontroller pin
DB4
RBO
DB5
RBI
DB6
RB2
RB7
RB3
E
RB4
RS
RB5
Analog input ANO (RAO)
RW pin of the LCD is connected to ground. The brightness of the LCD is
controlled by connecting a 5K variable resistor to pin VEE of the display.
Figure 5.107 (Continued)
298 PIC BASIC Projects
The PIC16F73 microcontroller has built in 8-bit 5 channel A/D converters.
The A/D reference voltage is set to +5 V With 8-bit converters, operating with
a reference voltage of +5V, the bit resolution is 5000/256 = 19.53mV.
The result is displayed in mV in the following format:
V = nnnn
This program is similar to LCD5.BAS, but here the result is more accurate since
the conversion factor is taken as 19.53 and not just 19.
In this program PicBasic statement ADCIN is used to read analog data
Author:
Dogan Ibrahim
Date:
November, 2005
Compiler:
PicBasic Pro
File:
LCD5-2.BAS
Modifications
DEFINITIONS
Define LCD connections
DEFINE LCD_DREG
PORTB
DEFINE LCD_DBIT
DEFINE LCD_RSREG PORTB
DEFINE LCD_RSBIT
5
DEFINE LCD_EREG
PORTB
DEFINE LCD_EBIT
4
DEFINE LCD_BITS
4
DEFINE LCD LINES
2
' LCD Data bits on PORTB
' PORTB starting address
' LCD RS bit on PORTB
' LCD RS bit address
' LCD E bit on PORTB
' LCD E bit address
' LCD in 4-bit mode
' LCD has 2 rows
' Define A/D converter parameters
DEFINE ADC_BITS 8
DEFINE ADC_CLOCK 3
DEFINE ADC_SAMPLEUS 50
Figure 5.107 (Continued)
' A/D number of bits
' Use A/D internal RC clock
' Set sampling time in us
PicBasic and PicBasic Pro projects 299
' Variables
Res Var Word
Volts 1 Var Word
Volts2 Var Word
' A/D converter result
' First part of result in mV
' Second part of result in mV
' Constants
Convl Con 19
Conv2 Con 53
TRISA = 1
TRISB =
PAUSE 500
' Initialize the A/D converter
ADCON1=0
ADCONO = %1 1000001
LCDOUT $FE, 1
AGAIN:
' Start A/D conversion
ADCIN 0, Res
Volts 1 =Res * Convl
Volts2 = Res * Conv2
Volts2 = Volts2/100
Volts 1 = Volts l+Volts2
LCDOUT $FE,2,"V = ",DEC4 Volts 1
PAUSE 1000
GOTO AGAIN
' 5000/256 = 19.53, this is the decimal part
' This is the fractional part
' RAO (AN0) is input
' PORTB is output
' Wait 0.5sec for LCD to initialize
' Make AN0 to AN4 as analog inputs,
' make reference voltage = VDD
' A/D clock is internal RC, select channel AN0
' Turn on A/D converter
' Clear LCD
' Read Channel data
' Multiply by 19
' Multiply by 53
' Result in mV
' Display result
' Wait 1 second
' Repeat
END ' End of program
Figure 5.107 PicBasic program using the ADCIN instruction
300 PIC BASIC Projects
Project 24
Project title:
LCD-based thermometer using A/D converter
Project description: In this project an LCD-based thermometer is designed. The project can be
used to display the temperature in degrees centigrade every second in the
following format:
Temp = nnC
Where nn is the measured temperature. Figure 5.108 shows the block dia-
gram of the project where the temperature sensor is connected to one of
the analog-to-digital converter (A/D) channels of a PIC microcontroller.
Temperature
sensor
Figure 5.108 Block diagram of Project 24
PIC
Microcontroller
Temp = nnC
LCD
Hardware:
The circuit diagram of the project is shown in Figure 5. 109.
In this project a PIC16F73-type microcontroller is used. This is a 28-pin
microcontroller with built-in 5 channel A/D converters, each having 8-
bits of resolution. The microcontroller is operated from a 4 MHz res-
onator. The temperature sensor used is the LM35DZ (see Figure 5.110)
3-pin analog sensor with a range of 0°C to + 100°C. LM35DZ provides
an analog output voltage which is proportional to the measured tempera-
ture. The device has 3 pins: Vs, Gnd, and Vo. Vs and Gnd are connected to
the supply voltage and the ground, respectively. It is recommended by the
manufacturers to use a 10 O resistor and a 1 |xF capacitor filter at the out-
put of the sensor to minimise electrical noise. Vo is the analog output volt-
age given by
Vo = 10mV/°C
For example, at a temperature of 20°C the output voltage is 200 mV. In
this project LM35DZ is connected to analog input AN0 of the PIC16F73
microcontroller.
PicBasic and PicBasic Pro projects 301
+
1
78L05
3
+5V
0.33 mFz
i
r- 0.01 [if
9V
Battery
i
2
1
A.IK
20
Temperature
Sensor
+5V
LM35DZ
1 —
10
Vdd
MCLR
RBO
RB1
RB2
RB3
RB4
RB5
ANO
PIC
16F73
Vss
OSC1
Vss
OSC2
9
T
21
11
22
12
23
13
24
14
25
set brightness
— c=i—
5K
DB4
DB5
DB6
DB7
VDD VEE
LCD
ERS VSS R/W
6 4
26
X
19
10
4 MHz resonator
Figure 5.109 Circuit diagram of Project 24
Figure 5.110 LM35DZ temperature sensor
Flow diagram:
The operation of the project is very simple: the output of the temperature
sensor is converted into digital, scaled, and then displayed on the LCD.
This process is repeated after one-second delay.
The flow diagram of the project is given in Figure 5.1 1 1. At the beginning
of the program LCD connections, port directions and the A/D converter are
configured. Analog temperature is then read and converted into digital. The
302 PIC BASIC Projects
reading is scaled, converted into true degrees centigrade temperature and
then displayed on the LCD. This process is repeated after one-second delay.
BEGIN
Configure LCD
connections
Configure port
directions
Configure A/D
converter
Start conversion
N /^ End of
* conversion ?
Read temperature
Scale and display
temperature
Wait 1 second
Figure 5.111 Flow diagram of Project 24
Software:
PicBasic
The PicBasic program of this project is complex since LCDs are not sup-
ported directly and the LCD routines developed in Project 20 use the
PicBasic and PicBasic Pro projects 303
default LCD connections. Only the PicBasic Pro program listing of this
project is given.
PicBasic Pro
The PicBasic Pro program listing of the project is given in Figure 5. 1 12. At
the beginning of the program LCD connections and the A/D parameters are
defined. Variable Res stores the converted data. A/D conversion is started
using the ADCIN statement. When the conversion is complete, the con-
verted data is available in register Res. The contents of Res can be converted
into millivolts by multiplying it by 19.53 as described in Project 23. But,
since the output of the sensor is 10mV/°C, it will be necessary to divide Res
by 10 in order to find the real absolute temperature in degrees centigrade.
Thus, the temperature can be obtained by the following operation:
Res * 19.53/10 = Res * 1.953 « 2 * Res
In the program, variable Res is multiplied by 2 to obtain the temperature
with a ±1°C accuracy (the resolution of the A/D converter is 19.53 mV
which is equivalent to nearly 2°C). The value of Res is then displayed on
the LCD as a two-digit decimal number. The above process is repeated
after one-second delay.
For more accurate temperature measurements an A/D converter with a
higher resolution will be required, e.g. 10-bit or higher.
LCD BASED THERMOMETER
In this project an LCD display is connected to a PIC16F73 microcontroller.
The microcontroller is configured to operate with a 4MHz external rezonator.
The project is a thermometer, which can measure the environmental
temperature and then display on the LCD.
A LM35DZ type analog output temperature sensor is used in this project.
LM35DZ provides an output voltage proportional to the measured temperature.
Figure 5.112 (Continued)
304 PIC BASIC Projects
The connection between the LCD display and the microcontroller is as follows:
Display
Microcontroller pin
DB4
RBO
DB5
RBI
DB6
RB2
RB7
RB3
E
RB4
RS
RB5
LM35DZ ANO (RAO)
RW pin of the LCD is connected to ground. The brightness of the LCD is
controlled by connecting a 5K variable resistor to pin VEE of the display.
The PIC16F73 microcontroller has built in 8-bit 5 channel A/D converters.
The A/D reference voltage is set to +5 V With 8-bit converters, operating with
a reference voltage of +5V, the bit resolution is 5000/256 = 19.53mV.
The temperature is displayed in degrees C in the following format:
TEMP = nnC
In this program PicBasic statement ADCIN is used to read analog data
Author: Dogan Ibrahim
Date: November, 2005
Compiler: PicBasic Pro
File: TEMPBAS
Modifications
DEFINITIONS
Define LCD connections
DEFINE LCD_DREG PORTB
DEFINE LCD_DBIT
Figure 5.112 (Continued)
' LCD Data bits on PORTB
' PORTB starting address
PicBasic and PicBasic Pro projects 305
DEFINE LCD_RSREG PORTB
DEFINE LCD_RSBIT 5
DEFINE LCD_EREG PORTB
DEFINE LCD_EBIT 4
DEFINE LCD_BITS 4
DEFINE LCD LINES 2
' LCD RS bit on PORTB
' LCD RS bit address
' LCD E bit on PORTB
' LCD E bit address
' LCD in 4-bit mode
' LCD has 2 rows
' Define A/D converter parameters
DEFINE ADC_BITS 8
DEFINE ADC_CLOCK 3
DEFINE ADC_SAMPLEUS 50
' Variables
' A/D number of bits
' Use A/D internal RC clock
' Set sampling time in us
Res Var Word
Tempi Var Byte
TRISA = 1
TRISB =
PAUSE 500
' Initialize the A/D converter
ADCON1=0
ADCONO = %1 1000001
LCDOUT $FE, 1
AGAIN:
' Start A/D conversion
' A/D converter result
' Temperature in degrees C
' RAO (AN0) is input
' PORTB is output
' Wait 0.5 sec for LCD to initialize
' Make AN0 to AN4 as analog inputs,
' make reference voltage = VDD
' A/D clock is internal RC, select AN0
' Turn on A/D converter
' Clear LCD
ADCIN 0, Res
Tempi = 2 * Res
LCDOUT $FE,2,"TEMP = ",DEC2 Tempi, "C"
PAUSE 1000
GOTO AGAIN
END
Figure 5.112 PicBasic Pro listing of Project 24
' Read Channel data
' Convert to degrees C
' Display decimal part
' Wait 1 second
' Repeat
' End of program
306 PIC BASIC Projects
Project 25
Project title:
Project description:
Serial LCD-based thermometer with external EEPROM memory
In this project an LCD-based thermometer is designed. The project con-
sists of a temperature sensor, a serial LCD display, a PIC microcontroller,
and an external I 2 C bus compatible EEPROM memory. Temperature is
measured every minute and stored in the EEPROM memory. During this
time the following message is displayed on the LCD:
COLLECTING DATA
After 1 h the measurement stops and the program reads from the EEPROM
memory to find the maximum temperature. The maximum temperature is
displayed on the LCD in the following format:
Max=nnC
where nn is the measured maximum temperature in 1 h. Figure 5.113
shows the block diagram of the project where the temperature sensor is
connected to one of the analog-to-digital converter (A/D) channels of a
PIC microcontroller.
Temperature
sensor
PIC
Microcontroller
serial
LCD
Serial EEPROM
Memory
Figure 5.113 Block diagram of Project 25
Hardware:
The circuit diagram of the project is shown in Figure 5.1 14. In this project
a PIC16F73-type microcontroller is used. This is a 28-pin microcontroller
with built-in 5 channel A/D converters, each having 8-bits of resolution.
The microcontroller is operated from a 4 MHz resonator. The temperature
sensor used is the LM35DZ 3-pin analog sensor (see Project 24) with a
range of 0°C to +100°C. LM35DZ provides an analog output voltage
which is proportional to the measured temperature. The device has 3 pins:
Vs, Gnd, and Vo. Vs and Gnd are connected to the supply voltage and the
PicBasic and PicBasic Pro projects 307
ground, respectively. It is recommended by the manufacturers to use a
1011 resistor and a 1 (jlF capacitor filter at the output of the sensor to min-
imise electrical noise. Vo is the analog output voltage given by
Vo = 10mV/°C
EEPROM Memory
Temperature is stored every minute in an ST24C04-type serial I 2 C bus
compatible EEPROM memory, having a capacity of 512 X 8 bits, organ-
ised as 2 blocks of 256 bytes each. The memory is connected to the micro-
controller as an I 2 C device where the clock input (SCL) is connected to
port RBO of the microcontroller and the data pin (SDA) is connected to
port RBI of the microcontroller. Although any value pull-up resistors
from 1.8 to 47K can be used, in this project 4.7K resistors are used
for the I 2 C bus. ST24C04 is an 8-pin device with the following pin
descriptions:
Pin 1 : No connection
Pin 2: Device address Al
Pin 3: Device address A2
Pin 4: Gnd
Pin 5: Data line
Pin 6: Clock line
Pin 7: Write protect pin
Pin 8: Vcc.
The device address on the I 2 C bus consists of 7 bits
4-bit control code
2-bit device address (Al and A2)
1-bit block select (if more than one block is used).
Address is sent on the bus as an 8 -bit byte where the eighth bit is the R/W
control bit. R/W = to write to a device, and R/W = 1 to read from a
device. The 8-bit address format for the ST24C04 consists of the follow-
ing bits (b is the block-select bit sent by the Master):
1
1
A2
Al
B
R/W
In this project Al and A2 inputs are connected to ground so that the
memory-select address is hexadecimal $A0 (bit pattern "10100000") for
the first block of memory (256 bytes) when B = 0, and $A2 (bit pattern
"10100010") for the other block of memory (256 bytes) when B = 1.
Note that A 1 and A2 are not used by this memory chip (i.e. there are no
308 PIC BASIC Projects
internal connections to these pins). Write protect pin should be connected
to ground to enable writing to the device.
After writing a byte to the memory it is recommended by the manufacturers
to wait for about 10 ms before another byte is written or read.
1
r
9V | 0.33 uFzz
Battery | p ^
78L05
^r
Temperature
Sensor
3 + 5V
-r-0.01|jF
4.7K
+5V
LM35DZ
10
20
Vdd
RB2
MCLR
PIC
16F73
AN0
OSC1
RB0
RB1
Vss
Vss
OSC2
X
23
RX
VDD
LCD
ILM-216
Serial LCD
+5V4^
n
4.7K
22
19
10
4 MHz resonator
4.7K
6
8
Vcc A0
SCL A1
SDA A2
Gnd
24C04
WP
Serial EEPROM
-±- Adress = $A0
Figure 5.114 Circuit diagram of Project 25
Pin layout of the ST24C04 serial EEPROM memory is shown in
Figure 5.115.
24C04
0AO Vcc |
A1 WPf]
A2 SCL S]
HVss SDA |
Figure 5.115 Pin layout of ST24C04 memory
PicBasic and PicBasic Pro projects 309
Serial LCD
An ILM-216-type serial LCD is used in this project where the serial input
of the LCD is connected directly to RB2 port of the microcontroller. The
operation of this serial LCD is described in detail in Section 4.3.2. The
communication parameters have been selected as: 2400 baud, 8 data bits,
and no parity bit.
The operation of the project is very simple: the output of the temperature
sensor is converted into digital format every minute and then stored in
the EEPROM memory. Data is collected for 1 h (60 samples) and at the
end of this time the maximum temperature is found and displayed on the
serial LCD.
Flow diagram: The flow diagram of the project is given in Figure 5. 1 16. At the beginning
of the program the A/D converter parameters are defined, and port direc-
tions are configured. A loop is used to read the temperature every minute,
convert into degrees centigrade and store in the EEPROM memory. The
values stored in the EEPROM memory are then read and the maximum
value is found and displayed on the LCD.
Software: PicBasic
I 2 C input and output commands by default use the RAO and RA1 pins for
data and clock, respectively. Looking at the A/D configuration of
PIC16F73, it is not possible to configure RAO and RA1 as digital pins and
any other pin of PORTA as an analog channel. As a result of this, it is not
possible to implement this project using the PicBasic language unless the
I 2 C routines are modified.
PicBasic Pro
PicBasic Pro program listing of the project is shown in Figure 5.1 17. At the
beginning of the program the A/D converter parameters are defined, and
port directions are configured. The A/D converter is then initialised and
configured. A FOR loop is used where inside this loop the temperature is
read from the sensor every minute using the ADCIN statement, it is then
converted into degrees centigrade and stored in successive locations of the
EEPROM memory using the I2CWRITE statement. The loop is repeated
60 times (i.e. for 1 h) and the loop index (variable Addr) is used to address
the EEPROM memory. After the data collection another FOR loop is used
to read the temperature values from the EEPROM (using the I2CREAD
statement) memory and then find the largest temperature during the hour.
The maximum temperature is stored in variable Maxone and is displayed
on the LCD in the following format:
Max = nnC
3 10 PIC BASIC Projects
BEGIN
Define A/D parameters,
configure I/O ports
Display
"COLLECTING DATA"
Configure A/D
converter
Cnt = 1
Get a temperature
value
Store in EEPROM
Wait 1 minute
Cnt = Cnt + 1
N
Find max temperature
Display max temperature
END
Figure 5.116 Flow diagram of Project 25
PicBasic and PicBasic Pro projects 311
Notice that the PicBasic Pro statement SEROUT is used to send serial
data to the LCD. RB2 is defined as the serial output port (Sout) and the
baud rate is chosen as 2400. The include file "modedefs.bas" contains the
definitions for the various PicBasic Pro baud rates. SEROUT command
assumes a 4 MHz oscillator when generating its serial bit timing.
Note that the serial data must be inverted before sending to the serial LCD.
Mode "N2400" defines the baud rate as 2400 and also inverts the serial
output data.
SERIAL LCD BASED THERMOMETER WITH SERIAL EEPROM
In this project an LCD display is connected to a PIC16F73 microcontroller.
The microcontroller is configured to operate with a 4 MHz external rezonator.
The project is a thermometer with an external serial EEPROM.
The temperature is measured every minute and is stored in the EEPROM
memory. After one hour the measurement stops and the maximum
temperature during this time is found and displayed on the serial LCD.
A LM35DZ type analog output temperature sensor is used in this project.
LM35DZ provides an output voltage proportional to the measured temperature.
A 24C04 type serial EEPROm is used in the project.
A serial LCD is used in this project. The Baud rate is selected as 2400.
The connection between the LCD and the microcontroller is as follows:
Display Microcontroller pin
RX RB2
The connection between the microcontroller and the serial EEPROM is as
follows:
EEPROM Microcontroller pin
SCL RB0
SDA RBI
Figure 5.117 (Continued)
312 PIC BASIC Projects
The temperature sensor is connected to the microcontroller as follows:
Sensor
LM35DZ
Microcontroller pin
ANO (RAO)
The PIC16F73 microcontroller has built in 8-bit 5 channel A/D converters.
The A/D reference voltage is set to +5V. With 8-bit converters, operating with
a reference voltage of +5V, the bit resolution is 5000/256 = 19.53mV
The maximum temperature is displayed in degrees C in the following format:
Max=nnC
In this program PicBasic statement ADCIN is used to read analog data
Author:
Dogan Ibrahim
Date:
November, 2005
Compiler:
PicBasic Pro
File:
SERIAL.BAS
Modifications
INCLUDE "modedefs.bas"
DEFINITIONS
Define A/D converter parameters
DEFINE ADC_BITS 8
DEFINE ADC_CLOCK 3
DEFINE ADC SAMPLEUS 50
' A/D number of bits
' Use A/D internal RC clock
' Set sampling time in us
' Variables used
Symbol Sout = 2
Symbol SDA = PORTB.l
Symbol SCL = PORTB.O
Figure 5.117 (Continued)
' RB2 is serial output
' EEPROM Data pin
' EEPROM clock pin
PicBasic and PicBasic Pro projects 313
' Variables
Res
Var
Byte
Tempi
Var
Byte
Maxone
Var
Byte
Addr
Var
Byte
' A/D converter result
' Temperature in degrees C
' Maximum temperature
'Address of EEPROM
' Start of Program
TRISA = 1
TRISB =
' RAO (ANO) is input
' PORTB is output
PAUSE 500 ' Wait 0.5sec for LCD to initialize
' Clear display and display message "COLLECTING DATA..."
SEROUT Sout, N2400, [12, "COLLECTING DATA..."]
' Initialize the A/D converter
ADCON1=0
ADCONO = %1 1000001
' Make ANO to AN4 as analog inputs,
' make reference voltage = VDD
' A/D clock is internal RC, select channel ANO
' Turn on A/D converter
' Start A/D conversion and get 60 samples for an hour
FOR Addr = TO 59
ADCIN 0, Res ' Read Channel data
Temp 1=2* Res ' Convert to degrees C
I2CWRITE SDA, SCL, % 10 100000, Addr, [Tempi]
PAUSE 60000 ' Wait 1 minute
NEXT Addr ' Repeat
' Read all collected data from EEPROM and find and display the largest one.
TRISB = 2
Maxone =
FOR Addr = TO 59
I2CRead SDA, SCL, % 10 10000, Addr, [Tempi]
IF Temp 1 > Maxone THEN Maxone = Temp 1
NEXT Addr
Figure 5.117 (Continued)
' RB 1 is input now
' Initially maximum =
3 14 PIC BASIC Projects
' Max temperature is in variable Maxone.
' Clear display and display the value of Maxone
SEROUT Sout, N2400, [12, "Max = ",#Maxone,"C"]
END ' End of program
Figure 5.117 PicBasic Pro listing of Project 25
PicBasic and PicBasic Pro projects 315
Project 26
Project title: Programmable thermometer with RS232 serial output
Project description: In this project a programmable digital thermometer is designed and the
temperature readings are sent out at required intervals through an RS232
serial line. The project consists of a temperature sensor, a PIC microcon-
troller and an RS232 line.
The temperature is sent out either in degrees centigrade or in degrees
Fahrenheit in the following format:
nnC
nnC
or,
nnF
nnF
The thermometer can be connected to a serial line such as the COM1 or
COM2 port on a PC. A terminal emulator program such as Hyperlink,
SmarTerm, etc. can be activated on the PC to communicate with the ther-
mometer. The communication parameters should be set to 2400 Baud, 8
data bit, 1 stop bit, and no parity bit. When the thermometer is connected
to the PC and the terminal emulation program is activated the following
messages will be displayed on the screen. The texts entered by the user are
in bold for clarity:
Digital Thermometer With RS232 Output
Enter sampling interval in seconds : 1
Output in degrees C (C) or degrees F (F) : C
Press ENTER to start data collection...
Data collection started:
nnC
nnC
nnC
316 PIC BASIC Projects
Figure 5.118 shows the block diagram of the project where the tempera-
ture sensor is connected to one of the analog-to-digital converter (A/D)
channels of a PIC microcontroller.
PIC
Microcontroller
RS232-
Level
Converter
Temperature
sensor
RS232
Figure 5.118 Block diagram of Project 26
Hardware:
The circuit diagram of the project is shown in Figure 5.119. Any type of
PIC microcontroller with a built-in A/D converter can be used. In this
project a PIC16F877-type microcontroller is used. This is a popular
microcontroller having 40-pins and 8 channel 10-bit multiplexed built-in
A/D converter. The reason for choosing this microcontroller is to make
your-self familiar with this popular microcontroller.
LM35DZ analog temperature sensor is connected to bit of PORTA
(ANO). RBO and RBI are configured as RS232 serial output and input,
respectively. RS232 voltage levels are ± 12V where — 12V is called Mark
(logic 1) and + 12 V is called Space (or logic 0). Normally RS232 voltage
9V
Battery
0.33 pFd=
78L05
m
+5V
^0.01mF
4.7K
Temperature
Sensor
+5V
LM35DZ
10
^1mf
11
32
Vdd
MCLR
RBO
RB1
PIC
16F877
ANO
OSC1
Vss
Vss
OSC2
X
1uF
33tx11
16
34 r X 12
+
1MF
12
31
14
4 MHz resonator
MAX202
15
K
1uF
5i
4 s f a+ i
13
14
1uF
+
Q
O
Q
O
O
TO PC
RS232 Connector
Figure 5.119 Circuit diagram of Project 26
PicBasic and PicBasic Pro projects 317
levels are converted to CMOS levels using RS232-level converter chips,
such as the MAX202, MAX232, DS275, etc. An RS232-level converter
chip converts the to +5 V output from the microcontroller into ± 12 V
RS232 levels. Similarly, the RS232-level output from a device is con-
verted into to +5 V suitable for the microcontroller inputs.
MAX202 is a 16-pin IC having dual RS232 transmitters and receivers.
This IC requires external capacitors for its operation. Figure 5.120 shows
the connection diagram when one of the channels of MAX232 is used.
+5V
10mF
16^2
licrocontrollerTXo
licrocontroller RXo
9-pin RS232 Connector
Figure 5.120 MAX232 RS232-level converter
DS275 is a smaller chip with only 8-pins. This IC also includes a trans-
mitter and a receiver. The advantage of DS275 is there is no need to use
external capacitors. Figure 5.121 shows the connection diagram when the
DS275 is used.
Microcontroller TX o
licrocontroller RXo
Figure 5.121 DS275 RS232 level converter
9-pin RS232 Connector
318 PIC BASIC Projects
In an asynchronous RS232 communication, data is sent and received as
frames. A frame consists of a start bit, 7 or 8 data bits, an even or odd par-
ity bit, and a stop bit. In many applications a 10-bit frame is used to send
a data byte with the following characteristics:
• 1 start bit
• 8 data bits
• no parity bit
• 1 stop bit.
The data line is normally at logic 1 (MARK) and this is the idle state of
the line. Communication starts by sending the start bit which is a logic 0,
sent for the duration of the bit-time. Then the 8 data bits are sent, each
separated with the bit-time. Communication stops by sending the stop bit.
The bit-time depends on the Baud rate chosen. Typical baud rates are:
2400, 4800, 9600, 19,200, 38,400, etc. For example, when using a 9600
baud rate, 9600 bits of information are sent each second. The bit-time is
then 1000/9600 = 0.104 ms, or 104 ms. Since a data byte consists of 10
bits, this is equivalent to sending 960 characters per second.
RS232-level converter chips invert the data and as a result of this the
SEROUT command should be used in true mode (e.g. T2400 for 2400
baud).
As shown in Figure 5.122, two types of RS232 connector are available:
9-pin D-type, and 25 -pin D-type connector. Minimum signals required
for RS232 communication are: transmit (TX), receive (RX), and ground.
The pin numbers for both types of connectors are
Function
9-way
25 -way
TX
2
2
RX
3
3
GND
5
7
'O
C> CUX.0
o
o
o
a &
OJOJOJOJOJOJOJOJOJOJOJO
o
o
o
o
o
o
o
o
o
o
o
a
Figure 5.122 RS232 connectors
Flow diagram:
The flow diagram of the project is shown in Figure 5.123. At the begin-
ning of the program I/O ports and the A/D are configured. Then the head-
ing is displayed and the user is prompted to enter the sampling interval
PicBasic and PicBasic Pro projects 319
and the mode as either C (degrees C) or F (degrees F). The program then
enters a loop where the temperature is read from the sensor, converted
into digital, scaled and then sent to the RS232 port of the microcontroller.
The program then waits for the amount of sampling interval and the above
process is repeated.
f BEGIN J
t
Configure I/O ports
V
Configure A/D
converter
i
'
Display heading
i
r
Read sampling
interval
^
r
Read mode (degrees
C or degrees F)
i
'
Get temperature
i
'
Scale temperature
i
r
Send temperature
to RS232 port
i
'
Wait for
sampling interval
i
'
Figure 5.123 Flow diagram of Project 26
Software:
PicBasic
The PicBasic program listing of the project is shown in Figure 5.124.
At the beginning of the program addresses of SFR registers used in the
320 PIC BASIC Projects
program and the variables are defined. Symbols RS232_out and RS232_in
are assigned to and 1, respectively which denote RBO and RB 1. PORTA
and PORTB directions are then configured. Notice that when the micro-
controller is powered up the RS232 port output may be at logic and this
may cause some unwanted data to be sent to the receiving device. In order
to avoid this, RS232 port output (RBO) is set to logic 1 for about 100ms.
Then the heading is sent to the RS232 port and the user is prompted to
enter the sampling interval and the type of output requested, i.e. degrees
Centigrade or degrees Fahrenheit. Serial outputs are sent using the
SEROUT statements. Similarly, serial inputs are received using the SERIN
statements.
The A/D converter is then initialised and the conversion is started by set-
ting bit 2 of ADCON to logic 1 . When the conversion is complete the
upper two bits of the 10-bit result is available in register ADRESH and
this is copied to variable Resh. Similarly, low 8-bits are available in vari-
able ADRESL and is copied to variable Resl. Variable Res stores the 10-bit
result of the conversion.
The A/D converter has a resolution of 10-bits. Thus, it is required to mul-
tiply the value read from the A/D converter with 5000/1024 so that we
obtain the reading in millivolts. The temperature sensor output is
10 mV/°C and thus, it will be necessary to divide the result by 10 in
order to obtain the result in degrees Centigrade. Thus, the required oper-
ation is 5000/(1024 X 10) = 0.48. In the program, the A/D reading is
multiplied by 48 and then divided by 100 to have the final result as true
degrees centigrade of temperature.
In the final part of the program the temperature is converted into degrees
Fahrenheit if the mode has been selected as "F". The temperature is then
sent to the RS232 port. The process repeats after a delay of TSample
milliseconds.
PROGRAMMABLE THERMOMETER WITH RS232 OUTPUT
In this project an analog temperature sensor (LM35DZ) is connected to one of
the A/D channels of a PIC16F877 microcontroller. The microcontroller is
operated from a 4 MHz external rezonator.
Figure 5.124 (Continued)
PicBasic and PicBasic Pro projects 321
The thermometer is connected to either COM 1 or the COM2 serial port
of a PC. A terminal emulation program, such as the Hyperterminal is
activated on the PC to communicate with the thermometer. During this
communication the user is prompted to enter the sampling interval and the
mode of the output required (degrees C or degrees F).
A typical communication between the thermometer and the PC is as
follows (in this example the sampling interval is selected as 2 seconds, and
the output is requested in degrees C):
Digital Thermometer With RS232 Output
Enter sampling interval in seconds: 2
Output is degrees C (C) or degrees F (F) : C
Press ENTER to start data collection...
Data collection started:
nnC
nnC
PORTB pins RBO and RB 1 are configured as RS232 TX and RX lines respectively.
RBO is connected to pin 2 of the RS232 connector. Similarly, RB 1 is connected
to pin 3 of the RS232 connector. The communication parameters are selected as
follows:
2400 baud
1 start bit
8 data bits
No parity
1 stop bit
The temperature sensor is connected to the microcontroller as follows:
Sensor Microcontroller pin
LM35DZ ANO (RAO)
The PIC16F877 microcontroller has built in 10-bit 8 channel A/D converters.
The A/D reference voltage is set to +5V
Figure 5.124 (Continued)
322 PIC BASIC Projects
In this program PicBasic statement ADCIN is used to read analog data
Author:
Dogan Ibrahim
Date:
November, 2005
Compiler:
PicBasic
File:
RS232-1.BAS
Modifications
DEFINITIONS
Symbol ADCON0 = $ IF
Symbol ADCON1 = $9F
Symbol ADRESH = $ IE
Symbol ADRESL = $9E
Symbol TRISA = $85
Symbol TRISB = $86
Symbol PORTA = $05
Symbol PORTB = $06
' Address
' Address
' Address
' Address
' Address
' Address
' Address
' Address
ofADCONO
ofADCOnl
of ADRESH
of ADRESL
of TRISA
of TRISB
of PORTA
of PORTB
' VARIABLES
Symbol Mode = B1
Symbol D = B2
Symbol Dummy = B3
Symbol TSample = W2
Symbol Resl = W3
Symbol Resh = W4
Symbol Res = W5
Symbol Tempi = W6
' Mode (C or F)
' Sampling time (seconds)
' Temperature
' SYMBOLS
Symbol RS232_out =
Symbol RS232_in = 1
Figure 5.124 (Continued)
' RBO is RS232 output
'RBI is RS232 input
PicBasic and PicBasic Pro projects 323
' CONSTANTS
Symbol CR = 13
Symbol LF = 10
POKE TRIS A, 1
POKE TRISB, 2
POKE PORTB, 1
PAUSE 100
' Carriage-return character
' Line-feed character
' RAO (ANO) is input
' RB0=output, RBl=input
' Send Heading
Again:
SEROUT RS232_out, T2400, (LF,CR, "Digital Thermometer With RS232 Output")
SEROUT RS232_out, T2400, (LF,CR, " ==============================")
SEROUT RS232_out, T2400, (LF,LF,CR, "Enter sampling interval in seconds : ")
SERIN RS232_in, T2400, #TSample
SEROUT RS232_out, T2400, (#Tsample)
SEROUT RS232_out, T2400, (LF,CR, "Degrees C (C) or degrees F (F) : ")
SERIN RS232_in, T2400, Mode
SEROUT RS232_out, T2400, (Mode)
SEROUT RS232_out, T2400, (LF,CR, "Press ENTER to start...")
SERIN RS232_in, T2400, Dummy
SEROUT RS232_out, T2400, (LF,CR)
TSample = TSample*1000
' Initialize the A/D converter
POKEADCON1, %10001110
POKE ADCON0, %0 1000001
' Make ANO analog input,
' make reference voltage = VDD
' A/D clock is internal, select channel ANO
' Turn on A/D converter
More:
' Start A/D conversion and get 60 samples for an hour
Figure 5.124 (Continued)
324 PIC BASIC Projects
D = "C
PEEKADCONO, BO
Bit2 = 1
POKE ADCONO, BO
' Start A/D conversion
WT: Pause 1
PEEKADCONO, BO
IF Bit2 = 1 THEN WT
PEEKADRESH, Resh
PEEK ADRESL, Resl
Res = Resh*256 + Resl
' Get high byte
' Get low byte
Tempi =48 * Res
Tempi =Templ/100
IF Mode = "C" THEN Cent
Tempi = Tempi * 18
Tempi = Tempi +320
Tempi = Tempi / 10
D = "F"
' Convert to degrees C
' If Fahrenheit
Cent:
SEROUT RS232_out, T2400, (LF,CR, #Templ, D)
PAUSE TSample
GOTO More
END
Figure 5.124 PicBasic listing of Project 26
' End of program
PicBasic Pro
The PicBasic Pro program listing of the project is shown in Figure 5.125.
At the beginning of the program the A/D parameters are defined. Symbol
RS232_out and RS232_in are defined as the RS232 output and input
ports, respectively.
The main program starts with label Again where the heading text is sent to
the RS232 port. Then the user is requested to enter the sampling interval in
seconds. The received value is stored in variable TSample. If the user does
not enter any characters in 5 s (5000 ms), the SERIN input routine times
PicBasic and PicBasic Pro projects 325
out and program jumps to label ESample, where the input is requested
again. Similarly, the user is requested to enter the output mode as either
degrees C or as degrees F. The required mode of temperature is stored in
variable Mode. If the user does not enter any characters in 5 s, the SERIN
input routine times out and jumps to label EMode.
The AD converter is then initialised by configuring registers ADCON1
and ADCONO. A/D conversion is started by the ADCIN instruction. The
A/D converter has a resolution of 10-bits. Thus, it is required to multiply
the value read from the A/D converter with 5000/1024 so that we obtain
the reading in millivolts. The sensor output is 10mV/°C and thus, it
will be necessary to divide the result by 10 in order to obtain the
result in degrees Centigrade. Thus, the required operation is 5000/
(1024 X 10) = 0.48. In the program the A/D reading is multiplied by 48
and then divided by 100 to have the final result as true degrees centigrade
of temperature.
In the final part of the program the temperature is converted into degrees
Fahrenheit if the mode has been selected as "F". The temperature is then
sent to the RS232 port. The process repeats after a delay of TSample
milliseconds.
PROGRAMMABLE THERMOMETER WITH RS232 OUTPUT
In this project an analog temperature sensor (LM35DZ) is connected to one of
the A/D channels of a PIC16F877 microcontroller. The microcontroller is
operated from a 4 MHz external rezonator.
The thermometer is connected to either COM1 or the COM2 serial port
of a PC. A terminal emulation program, such as the Hyperterminal is
activated on the PC to communicate with the thermometer. During this
communication the user is prompted to enter the sampling interval and the
mode of the output required (degrees C or degrees F).
A typical communication between the thermometer and the PC is as
follows (in this example the sampling interval is selected as 2 seconds, and
the output is requested in degrees C):
Figure 5.125 (Continued)
326 PIC BASIC Projects
Digital Thermometer With RS232 Output
Enter sampling interval in seconds: 2
Output is degrees C (C) or degrees F (F) : C
Press ENTER to start data collection...
Data collection started:
nnC
nnC
PORTB pins RBO and RBI are configured as RS232 TX and RX lines respectively.
RBO is connected to pin 2 of the RS232 connector. Similarly, RB 1 is connected
to pin 3 of the RS232 connector. The communication parameters are selected as
follows:
2400 baud
1 start bit
8 data bits
No parity
1 stop bit
The temperature sensor is connected to the microcontroller as follows:
Sensor Microcontroller pin
LM35DZ ANO (RAO)
The PIC16F877 microcontroller has built in 10-bit 8 channel A/D converters.
The A/D reference voltage is set to +5V.
In this program PicBasic statement ADCIN is used to read analog data
Author:
Dogan Ibrahim
Date:
November, 2005
Compiler:
PicBasic Pro
File:
RS232-2.BAS
Figure 5.125 (Continued)
PicBasic and PicBasic Pro projects 327
Modifications
INCLUDE "modedefs.bas"
DEFINITIONS
Define A/D converter parameters
DEFINE ADC_BITS 10
DEFINE ADC_CLOCK 3
DEFINE ADC SAMPLEUS 50
' A/D number of bits
' Use A/D internal RC clock
' Set sampling time in us
' VARIABLES
Tsample VARWord
Mode VAR Byte
Dummy VAR Byte
D VAR Byte
' Sampling time (seconds)
' Mode (C or F)
' Temperature mode display
' SYMBOLS
Symbol
RS232_
out =
=
Symbol
RS232_
.in =
1
1 CONSTANTS
CR
CON
13
LF
CON
10
' Variables
' RBO is RS232 output
'RBI is RS232 input
' Carriage-return character
' Line-feed character
Res Var Word
Temp 1 Var Word
' A/D converter result
' Temperature in degrees C
TRISA = 1
TRISB = 2
PAUSE 1000
Figure 5.125 (Continued)
' RAO (AN0) is input
' RBO = output, RB 1 = input
328 PIC BASIC Projects
' Send Heading to RS232 port
Again:
Esample:
EMode:
Estart:
SEROUT RS232_out, T2400, [LF,CR, "Digital Thermometer With RS232 Output"]
SEROUT RS232_out, T2400, [LF,CR, " ================"]
SEROUT RS232_out, T2400, [LF,LF,CR, "Enter sampling interval in seconds : "]
SERIN RS232_in, T2400, 5000, ESample, #TSample
SEROUT RS232_out, T2400, [#Tsample]
SEROUT RS232_out, T2400, [LF,CR, "Degrees C (C) or degrees F (F) : "]
SERIN RS232_in, T2400, 5000, EMode, Mode
SEROUT RS232_out, T2400, [Mode]
SEROUT RS232_out, T2400, [LF,CR, "Press ENTER to start..."]
SERIN RS232_in, T2400, 5000, Estart, Dummy
SEROUT RS232_out, T2400, [LF,CR]
TSample = TSample*1000
' Initialize the A/D converter
ADCONl = % 10001 110
ADCON0 = %0 1000001
' Convert to ms
' Make AN0 analog inputs,
' Reference voltage = VDD
' A/D clock is internal, Select channel AN0
' Turn on A/D converter
More:
' Start A/D conversion and get 60 samples for an hour
D = "C"
ADCIN 0, Res
' Read Channel data
Scale the reading to obtain degrees C. This involves multiplying by
5000/1024 and then diviing to 10 since the sensor output is lOmV/C. i.e.
We have to multiply the A/D readings with 5000/(1024 X 10) which
is equal to 0.48. We thus multiply by 48 and then divide by 100
Tempi =48 * Res
Tempi =Templ/100
Figure 5.125 (Continued)
' Convert to degrees C
PicBasic and PicBasic Pro projects 329
If the required output is degrees Fahrenheit, we have to perform the
operation: 1.8C + 32. Here, we are multiplying by 10. ie. Multiply by 18 and
add 320. The final result is then divided by 10.
IF Mode = "F" THEN ' If Fahrenheit selected
Temp 1 = Temp 1*18
Tempi = Tempi +320
Tempi = Tempi / 10
D = "F"
ENDIF
' Send temperature to RS232 port, wait for sampling time and repeat
SEROUT RS232_out, T2400, [LF,CR, #Templ, D]
PAUSE Tsample
GOTO More
END ' End of program
Figure 5.125 PicBasic Pro listing of Project 26
Figure 5. 126 shows a sample output obtained when the SmartTerm terminal
emulation program is used (we can use any type of terminal emulation soft-
ware) to communicate with the thermometer. In this example, the sampling
interval is selected as 4 s and the output is requested as degrees C.
The project built on a breadboard is shown in Figure 5.127.
330 PIC BASIC Projects
q c? y a p e? e a §> ► © § ^ o ?
Digital Thermometer With RS232 Output
Enter sampling interval in seconds : 4
Degrees C (C) or degrees F (F) : C
Press ENTER to start. ..
Al.-n Vhimn ftapg j
Figure 5.126 Sample output taken from the PC screen
Figure 5.127 Project built on a breadboard
PicBasic and PicBasic Pro projects 331
Project 27
Project title:
Project description:
Electronic organ
This is a simple electronic organ project. A small speaker is connected to
PORTA of a PIC microcontroller. Eight push-button switches are con-
nected to PORTB to act as the keyboard for the electronic organ. Only one
octave (eight notes) is provided in this project.
Figure 5.128 shows the block diagram of the project.
PIC
Microcontroller
CDEF
G ABC
8 Keyboard switches
Figure 5.128 Block diagram of Project 27
Speaker
Hardware:
The circuit diagram of the project is shown in Figure 5.129. Although any
model of PIC microcontroller with at least 9 I/O pins can be used, a
PIC16F627 microcontroller is used in this project. The microcontroller is
operated from an external 4 MHz resonator. A small speaker is connected
to bit of PORTA (RAO) using a 10 (jlF electrolytic capacitor.
Keyboard switches are connected to PORTB. Bit is assigned to musical
note C, bit 1 is assigned to note D, bit 2 is assigned to note E, and so on.
The switches are normally held at logic HIGH using the internal PORTB
pull-up resistors. Pressing a switch sends a logic LOW to the correspon-
ding microcontroller input port pin.
In this project, the following octave of notes is used:
Switch
1
2
3
4
5
6
7
8
Note
C
D
E
F
G
A
B
C
Frequency
262
294
330
349
392
440
494
524
Flow diagram:
The program continuously checks the switches and if any switch is
pressed then the musical note corresponding to that switch position is sent
to the speaker.
The flow diagram of the project is shown in Figure 5.130. At the begin-
ning of the project PORTA and PORTB directions are configured and
332 PIC BASIC Projects
9V
Battery
0.33 uFdz
78L05
^
+5V
-i-0.01uF
Speaker
4 MHz resonator
Figure 5.129 Circuit diagram of the project
BEGIN
Configure PORTA
and PORTB
directions
Set PORTB pull-ups
Send musical note
for this key to the
speaker
Wait 5ms
Figure 5.130 Flow diagram of Project 27
PicBasic and PicBasic Pro projects 333
PORTB internal pull-up resistors are enabled. The program then enters an
endless loop where the switches are checked. If a switch is pressed, then the
musical note corresponding to that switch position is sent to the speaker.
The program waits for 5 ms and then the above process is repeated.
Software: PicBasic
PicBasic language does not have an instruction to generate a signal with
the required frequency. A signal with a required frequency can be gener-
ated using the timer interrupt. But unfortunately, PicBasic language does
not support the use of interrupts from a high-level language. As a result of
this, it is not very easy to generate musical notes from the PicBasic lan-
guage. Only the PicBasic Pro program of this project is given here.
PicBasic Pro
The PicBasic Pro program listing of the project is shown in Figure 5. 1 3 1 . At
the beginning of the program the frequencies of musical notes are stored in
an array called Notes. Then, PORTB is configured as input and PORTA
is configured as output. PORTB internal pull-up resistors are then enabled
so that the switches are normally held at logic HIGH. The statement IF
PORTB <> 255 is true if any switch is pressed. The status of PORTB is
then inverted and the bit which is is the bit position pressed by the user.
For example, if the user pressed switch 5, number 16 will be obtained.
Normal state of PORTB 11111111
State when key 4 is pressed 11101111
State when PORTB inverted 10
PicBasic Pro statement NCD is used to obtain the bit position of the
switch pressed. In the above example, if p is the state of PORTB when
inverted, then,
y = NCD p
will return 5 in variable y, i.e. bit position 5 is set in variable p. Thus, the
statement
Key_pressed = NCD Key
returns the switch number (1 to 8) pressed. This number is then used as an
index in array Notes and the PicBasic Pro statement FREQOUT is used to
send the frequency of the required note to the speaker. The note is sounded
for a duration of 5 ms.
334 PIC BASIC Projects
SIMPLE ELECTRONIC ORGAN
In this project a small speaker is connected to bit of PORTA of a PIC16F627
microcontroller. Also, 8 push-button switches are connected to PORTB
of the microcontroller. The switches are used to represent the musical notes
C to C (i.e. one octave). The switch assignments are as follows:
Switch
Musical note
RBO
C
RBI
D
RB2
E
RB3
F
RB4
G
RB5
A
RB6
B
RB7
C
The frequencies of the notes used are as follows:
Note
Frequency (Hz)
C
262
D
294
E
330
F
349
G
392
A
440
B
494
C
524
When a switch is pressed, the frequency of the musical note corresponding
to that switch is sent to the speaker.
The project can be used to play simple tunes.
Figure 5.131 (Continued)
PicBasic and PicBasic Pro projects 335
Author:
Dogan Ibrahim
Date:
December, 2005
Compiler:
PicBasic Pro
File:
SOUND LB AS
Modifications
' DEFINITIONS
Speaker
VAR
PORTA.O
Notes
VAR
Word[9]
Key
VAR
Byte
Key_pressed
VAR
Byte
' Speaker is connected to RAO
' Frequencies of musical notes
' Key pressed
' Define the frequencies of musical notes
Notes[l] = 262 : Notes[2] = 294
Notes[5] = 392 : Notes[6] = 440
' Configure PORT directions
TRISB = % 1 1 1 1 1 1 1 1
TRISA =
OPTION_REG.7 =
CMCON = 7
: Notes[3] = 330
: Notes [7] = 494
: Notes [4] = 349
: Notes[8] = 524
' PORTB is input (keys)
' PORTA (RAO) is output
' Enable internal PORTB pull-ups
' Make RAO digital I/O
' Check if any key is pressed, and if so, find the musical note corresponding
' to the pressed key and send the frequency of this note to the speaker.
Loop:
IF PORTB <> 255 THEN
Key = -PORTB
Key_pressed = NCD Key
FREQOUT Speaker,5,Notes [Key_pressed]
ENDIF
GOTO Loop
END
Figure 5.131 PicBasic Pro listing of the project
' Check if any key pressed
' Invert key pattern
' Get key pressed
' Send note to speaker
' Repeat
' End of program
336 PIC BASIC Projects
Improving the musical tones
The tones generated by the statement FREQOUT are square wave and
they are very noisy. One way to improve the quality of these tones is by
filtering the output of the microcontroller signal. Figure 5.132 shows a
simple filter that can be used to obtain a cleaner waveform when the FRE-
QOUT statement is used.
In many applications, the amplitude of the output signal may not be ade-
quate and it may be necessary to amplify this signal. Figure 5.133 shows
an amplifier circuit which can be used to increase the output signal level
of our electronic organ.
Microcontrollero
10mF
-ID-
1K
1K
i^rr
-O Speaker
0.1 uF
I I
0.1 uF
Figure 5.132 A simple filter
A+5V
Microcontrollero
Speaker
Figure 5.133 Amplifying the output signal
It is also recommended to use a higher oscillator frequency, e.g. 20 MHz
for an improved output response. This will require the use of a 20 MHz
crystal, and a PIC chip which can operate at 20 MHz. The following line
of code should also be added to the program to show that we are using a
20 MHz crystal, and not the default 4 MHz.
DEFINE OSC 20
PicBasic and PicBasic Pro projects 337
Project 28
Project title:
Unipolar stepping motor control
Project description: This project is about the control of an unipolar stepping motor using a PIC
microcontroller. The project shows how a stepping motor can be con-
trolled to rotate clockwise for the required number of revolutions.
In this project the stepping motor is controlled as follows:
Rotate 100 revolutions clockwise
Stop
Figure 5.134 shows the block diagram of the project. Four output ports of
the microcontroller are connected to MOSFET transistors which drive the
stepping motor.
PIC
Microcontroller
Driver
1
►/
►
►
Figure 5.134 Block diagram of Project 28
Hardware:
The circuit diagram of the project is shown in Figure 5.135. In this proj-
ect a PIC16F627-type microcontroller, operated with its internal 4 MHz
clock is used. The master clear circuit is enabled during programming of
the chip. The stepping motor used in the project is the model UAG2 (see
Figure 5.136), manufactured by SAIA Schrittmotoren. This stepping
motor operates with 12 V, has 6 leads, and a stepping angle of 18°. Thus,
20 steps are required for a complete revolution. The motor consists of two
windings and the pin connections are as follows:
Pin
1
2
3
4
5
6
Function
Start of first winding
Start of second winding
Common point of first winding
Common point of second winding
End of first winding
End of second winding
338 PIC BASIC Projects
PORTB pins RB0-RB3 are connected to Gate inputs of four IRL1520N
type MOSFET power transistors which are used as switches. The Drain
outputs of these transistors are connected to motor windings as shown in
Figure 5.135. Common points of both windings are connected to +12V
supply using 68 II current-limiting resistors.
i
+ 12
Figure 5.135 Circuit diagram of Project 28
Figure 5.136 UAG2 unipolar stepping motor
PicBasic and PicBasic Pro projects 339
Flow diagram:
The flow diagram of the project is shown in Figure 5.137. At the begin-
ning of the project PORTB pins are configures as output. Pulses are then
sent to PORTB to rotate the motor 100 steps clockwise. The motor is then
stopped.
BEGIN
Configure PORTB
as output
Send pulses for
100 revolutions
clockwise rotation
END
Figure 5.137 Flow diagram of Project 28
Software:
PicBasic
PicBasic program listing of the project is given in Figure 5.138. At the
beginning of the program PORTB pins are configured as output. Variable
Revolutions stores the required number of revolutions which is 100 in this
example. Variable Pulses stores the number of pulses to be sent to the
motor. This variable is divided by 4 so that it stores the number of times
the patterns of 1,2,4,8 are to be sent to the motor. A FOR loop is used to
send the pulses to the motor. Pulses are sent as in the following order:
0001
0010
0100
1000
0001
340 PIC BASIC Projects
Notice that a 3 ms delay is used between each step output to the motor.
The RPM (number of revolutions per minute) of the motor can be calcu-
lated as follows:
If Tis the time between the steps, and /3 is the step angle of the motor, then
the motor rotates (5IT steps in 1 s. Since one revolution is 360°, the num-
ber of revolutions in one second is {M360T. The RPM is then given by
RPM = 60/3/3607
or,
RPM = /3/6T
In this example, j8 = 18°, and T = 3 ms (0.003 s). Thus,
RPM = 18/6(0.003) = 1000
UNIPOLAR STEPPING MOTOR CONTROL
In this project an UAG2 type unipolar stepping motor is connected to pins
RB0-RB3 of PORTB of a PIC16F627 microcontroller. The microcontroller is
operated from its internal 4MHz clock.
The motor is operated as follows:
Turn motor 100 revolutions clockwise
Stop
Four IRL1520N type MOSFET power transistors are used as switches to
provide current to the motor.
Author: Dogan Ibrahim
Date: December, 2005
Compiler: PicBasic
File: MOTOR l.B AS
Modifications
Figure 5.138 (Continued)
PicBasic and PicBasic Pro projects 34 1
' Symbols
Symbol PORTB = $06
Symbol TRISB = $86
Symbol Revolutions = WO
Symbol Pulses =W1
Symbol J = B4
POKE TRISB,
Revolutions =100
Pulses = 20*Revolutions
Pulses = Pulses / 4
' PORTB address
' TRISB address
' Required number of revolutions
' Number of pulses to be sent
' Used in FOR loop
' PORTB is output
' Required number of revolutions
' Required number of pulses
' Required number of steps
' Send Pulses to the motor for clockwise rotation. The number of revolutions is equal
' to Revolutions (100 in this example)
FOR J = 1 TO Pulses
POKE PORTB, 1
Pause 3
POKE PORTB, 2
Pause 3
POKE PORTB, 4
Pause 3
POKE PORTB, 8
Pause 3
NEXT J
END
Figure 5.138 PicBasic listing of Project 28
' End of program
PicBasic Pro
PicBasic Pro program listing of the project is given in Figure 5. 139. At the
beginning of the program TRISB is cleared to zero so that all PORTB pins
are configured as outputs. Variable Steps is defined as a byte array and
this array stores the bit patterns to be sent to the motor for clockwise rota-
tion. For example, sending the bit pattern . . .,1,2,4,8, . . . rotates the motor
clockwise by 4 steps. Variable Revolutions stores the required
number of revolutions which is 100 in this example. Variable Pulses
stores the number of pulses to be sent to the motor. This variable is
divided by 4 so that it stores the number of times the patterns of 1,2,4,8
are to be sent to the motor so that the motor rotates clockwise required
342 PIC BASIC Projects
number of revolutions. Two FOR loops are used in the program. The outer
loop controls the number of steps to be sent, and the inner loop sends the
bit patterns of 1,2,4,8 to the motor, as in the PicBasic program, the motor
rotates with a speed of RPM = 1000.
UNIPOLAR STEPPING MOTOR CONTROL
In this project an UAG2 type unipolar stepping motor is connected to pins
RB0-RB3 of PORTB of a PIC16F627 microcontroller. The microcontroller is
operated from its internal 4MHz clock.
The motor is operated as follows:
Turn motor 100 revolutions clockwise
Stop
Four IRL1520N type MOSFET power transistors are used as switches to
provide current to the motor.
Author:
Dogan Ibrahim
Date:
December, 2005
Compiler:
PicBasic Pro
File:
MOTOR2.BAS
Modifications
' Variables
Steps
Var
Byte[4]
' Step bit patterns
Revolutions
Var
Word
' Required number of revolutions
Pulses
Var
Word
' Number of pulses to be sent
I
Var
Byte
' Used in FOR loop
J
Var
Word
' Used in FOR loop
TRISB =
Figure 5.139 (Continued)
' PORTB is output
PicBasic and PicBasic Pro projects 343
' Define data to be sent to the motor
Steps [0] = 1
Steps[l] = 2
Steps[2] = 4
Steps[3] = 8
Revolutions =100
Pulses = 20*Revolutions
Pulses = Pulses / 4
' Required number of revolutions
' Required number of pulses
' Required number of steps
' Send Pulses to the motor for clockwise rotation. The number of revolutions is equal
' to Revolutions (100 in this example)
FOR J = 1 TO Pulses
FOR I = TO 3
PORTB = Steps[I]
PAUSE 3
NEXT I
NEXT J
STOP
END
Figure 5.139 PicBasic Pro listing of Project 28
' End of program
344 PIC BASIC Projects
Project 29
Project title:
Project description:
Unipolar stepping motor control using UCN5804B
This project is similar to Project 28, but here the stepping motor is con-
trolled using a UCN5804B type motor controller IC. In this project the
motor is rotated continuously. Motor direction is controlled using a but-
ton. Normally the motor rotates in one direction, and when the button is
pressed the direction is reversed.
Figure 5.140 shows the block diagram of the project.
+
V
PIC
Microcontroller
Direction
UCN
5804B
J
*\
Motor
Figure 5.140 Block diagram of Project 29
Hardware:
Flow diagram:
Software:
The circuit diagram of the project is shown in Figure 5.141. In this pro-
ject a PIC16F627-type microcontroller, operated with its internal 4-MHz
clock is used. Same stepping motor as in Project 28 is used. RBO port of
the microcontroller is connected to STEP input of the UCN5804B.
Direction of the motor is controlled from a button connected to the DIR
input. OutA, OutB, OutC, and OutD outputs of the IC are connected to
the windings of the motor. KaC and KbD are the common outputs con-
nected to the common points of the motor windings. Motor is rotated by
one step each time a pulse is applied to the STEP input of the IC.
The flow diagram of the project is shown in Figure 5.142. The operation
of the project is very simple. After PORTB is configured as output, pulses
are sent to UCN5804B continuously with 3 ms delay between each out-
put. As in the previous project, the speed of rotation is 1000 RPM.
PicBasic
PicBasic program listing of the project is given in Figure 5.143. At the
beginning of the program PORTB is configured as output. Pulses are then
sent to RBO with 3ms delay between each output.
PicBasic and PicBasic Pro projects 345
Q+12V
Q+5V
16
VDD
DIR OutB
Kbd
UCN5804B OutD
OutC
Kac
OutA
STEP
6
7
8
M J Stepping motor
RAAAn
1514 1 5|12|13|9|10| 2p T T
1 1 1 1 I 1 I 1 ^— C I 1 1 I 4
Figure 5.141 Circuit diagram of Project 29
f BEGIN J
i
r
Configure PORTB
as output
i
r
Send pulses to
UCN5804B
i
f
3ms Delay
Figure 5.142 Flow diagram of Project 29
PicBasic Pro
PicBasic Pro program listing of the project is given in Figure 5.144. The
project is very simple. At the beginning of the Project PORTB is config-
ured as output. Pulses are then sent to port pin RBO with 3 ms delay
between each output.
346 PIC BASIC Projects
UNIPOLAR STEPPING MOTOR CONTROL
In this project an UAG2 type unipolar stepping motor is used.
A UCN5804B type motor controller IC is used to control the motor. This IC
is controlled using two of its inputs: STEP and DIR. DIR is a logical input and
controls the direction of rotation. The motor rotates a step each time a pulse
is applied to the STEP input.
The motor rotates continuosly.
There is a delay of 3ms between each step.
Author:
Dogan Ibrahim
Date:
January, 2005
Compiler:
PicBasic
File:
MOTOR3.BAS
Modifications
Symbols
Symbol PORTB = $06
Symbol TRISB = $86
' PORTB address
' TRISB address
POKE TRISB,
' PORTB is output
POKE PORTB,
' Clear STEP to start with
More:
POKE PORTB, 1
POKE PORTB,
PAUSE 3
GOTO More
' Set STEP = 1
' Set STEP =
' Wait 3ms
' Repeat
END ' End of program
Figure 5.143 PicBasic listing of Project 29
PicBasic and PicBasic Pro projects 347
UNIPOLAR STEPPING MOTOR CONTROL
In this project an UAG2 type unipolar stepping motor is used.
A UCN5804B type motor controller IC is used to control the motor. This IC
is controlled using two of its inputs: STEP and DIR. DIR is a logical input and
controls the direction of rotation. The motor rotates a step each time a pulse
is applied to the STEP input.
The motor rotates continuosly.
There is a delay of 3ms between each step.
Author:
Dogan Ibrahim
Date:
January, 2005
Compiler:
PicBasic Pro
File:
MOTOR4.BAS
Modifications
Variables
Step_input Var PORTB.O
' Assign Step_input to RBO
TRISB =
' PORTB is output
More:
Step_input =
Step_input = 1
Step_input =
Pause 3
GOTO More
' Clear STEP to start with
' Set STEP = 1
' Set STEP =
' Wait 3ms
' Repeat
END ' End of program
Figure 5.144 PicBasic Pro listing of Project 29
348 PIC BASIC Projects
Project 30
Project title:
Project description:
Servomotor-based mobile robot control
Mobile robots are used in many industrial, commercial, research, and
hobby applications. This project is about the control of a mobile robot using
servomotors. The robot used in this project is the base of a popular mobile
robot known as Boe Bot, developed by Parallax (www.parallax.com and
www.stampinclass.com). The basic robot is controlled from a Basic Stamp
controller (Trademark of Parallax Inc.). The robot base and electronic cir-
cuit have been modified by the author so that the robot can be used with
PIC microcontrollers (see Figure 5.145).
The robot consists of two side drive wheels and a caster wheel at the back.
The drive wheels are connected to servomotors. A breadboard is placed on
the robot base for the electronic control circuit. The robot is driven from a
9V battery, and a 78L05-type voltage regulator is used to obtain +5V to
supply power to the microcontroller circuit.
In this project programs are developed to move the robot forward, back-
ward, and to turn left and right.
Figure 5.145 Robot used in the project
Hardware:
The circuit diagram of the project is shown in Figure 5.146. In this proj-
ect a PIC16F84 microcontroller is used and the microcontroller is oper-
ated with a 4 MHz crystal.
PicBasic and PicBasic Pro projects 349
Servomotors are used to drive the left wheel and the right wheel. A ser-
vomotor has three leads: power supply, ground, and the signal pin. Left
servomotor is connected to bit of PORTB (RBO), and right servomotor
is connected to bit 1 of PORTB (RBI). Although some servomotors can
operate with +5V supply, most servomotors require 6-9 V to operate.
+6-9 V
Regulator
78L05
I6-9V
+5V
I
+ R1
C3^2.2 M F
4.7K
14
VDD
MCLR
RBO
PIC
16F84
RB1
Vss
OSC1 OSC2
LEFT
SERVO
RIGHT
SERVO
>fT 4 MHZ ~T:
C1->- I 1 - 1 ! ->- C2
22pFT 4 MHZ ~T 22 P F
Figure 5.146 Circuit diagram of Project 30
Operating the servomotor
As described in Section 4.7 the servomotors used in robotic applications are modified servos
where the motor can rotate in either direction continuously by applying pulses to the servomotor.
In a modified servomotor typically a pulse with a width of 1.3 ms rotates the motor clockwise at full
speed. A pulse with a width of 1 .7 ms rotates the motor anti-clockwise, and a pulse with a width of
1.5 ms stops the motor. Figure 5.147 shows typical pulses used to drive modified servomotors.
The pulse required to operate a servomotor can very easily be obtained using the PULSOUT
statement of the PicBasic and PicBasic Pro compilers. When a 4 MHz crystal is used, the time
interval of PULSOUT is in units of 10 |xs. For example, the following PicBasic statement gener-
ates a pulse with a width of 1.3 ms from bit of PortB (1.3 ms = 1300 |xs and 1300/10 = 130):
PULSOUT 0, 130
350 PIC BASIC Projects
1.3 ms
Clockwise
-20 ms-
1.5 ms
Stop
1.7 ms
Anti-clockwise
Figure 5.147 Pulses used to drive modified servomotors
Similarly, the following PicBasic statement generates a pulse with a width of 1.7 ms from bit 1 of
PORTB:
PULSOUT 1, 170
A single pulse rotates the servomotor by a small amount. For a continuous rotation we have to
apply the pulses continuously. In most applications a loop is formed in software and pulses are
sent to the servomotor continuously. A delay is inserted between each pulse. The duration of this
delay determines the speed of the motor and about 20 ms is most commonly used value.
The following PicBasic (or PicBasic Pro) code shows how a servomotor connected to port RBO
can be rotated clockwise continuously:
Loop:
PULSOUT 0, 130
PAUSE 20
GOTO Loop
' Send a pulse
'Wait 20 ms
' Repeat
Similarly, the following PicBasic (or PicBasic Pro) code shows how a servomotor connected to
port RBI can be rotated anti-clockwise continuously:
Loop:
PULSOUT 1, 170
PAUSE 20
GOTO Loop
' Send a pulse
'Wait 20 ms
' Repeat
PicBasic and PicBasic Pro projects 351
You can experiment by varying the pulse width and the delay to see how the speed of the motor
changes.
Forward movement
Assuming that two side wheels are connected to servomotors, the robot moves forward when
Left wheel rotates anti-clockwise
Right wheel rotates clockwise
In this project, the left servomotor is connected to port pin RBO and right servomotor is connected
to port pin RBI. The following PicBasic (or PicBasic Pro) code can then be used to move the
robot forward:
Forward:
PULSOUT 0, 170
PULSOUT 1, 130
PAUSE 20
GOTO Forward
' Left wheel anti-clockwise
' Right wheel clockwise
'Wait 20 ms
' Repeat
Backward movement
Assuming that the two side wheels are connected to servomotors, the robot moves backward when
Left wheel rotates clockwise
Right wheel rotates anti-clockwise
In this project, the left servomotor is connected to port pin RBO and right servomotor is connected
to port pin RBI. The following PicBasic (or PicBasic Pro) code can then be used to move the
robot backward:
Backward:
PULSOUT 0, 130
PULSOUT 1, 170
PAUSE 20
GOTO Backward
' Left wheel clockwise
' Right wheel anti-clockwise
'Wait 20 ms
' Repeat
Moving the robot for required amount of time
The code given above moves the robot forward or backward continuously. There are applications
where we may want to mode the robot only required amount of time. For example, we may want
to move the robot forward for 5 s, then stop for 3 s, and then move backward for 2 s.
352 PIC BASIC Projects
We can adjust the movement time by using a FOR loop. The following code shows how we can
move the robot forward using a FOR loop:
FOR J = 1 TO M
PULSOUT 0, 170
PULSOUT 1, 130
PULSOUT 20
NEXT/
In this code variable M determines the number of times the loop is executed. Ignoring the small
time taken by the FOR and the NEXT statements, the time taken to execute only one iteration of
the FOR loop can be determined approximately as
FOR J = 1 TO M
PULSOUT 0, 170 1.7 ms
PULSOUT 1, 130 1.3 ms
PULSOUT 20 20.0 ms
NEXT /
23.0 ms
Thus, if the robot is required to move for T seconds (1000 X Tins) forward or backward, the value
of M to be used in the FOR loop can be calculated as follows:
M = 1000 X 7723
An example is given below.
Example 1
A mobile robot is controlled with two servomotors as shown in Figure 5.146. Write a PicBasic
program which will perform the following operations:
Move the robot forward for 4 s
Wait for 5 s
Move the robot backward for 3 s
Stop
Solution 1
The first action is to move the robot forward for 4 s. Thus, the value of M is
M = 4000/23 = 174
PicBasic and PicBasic Pro projects 353
Then the robot is required to stop for 5 s and then move backward for 3 s. The value of M for this
movement is
M = 3000/23 = 130
The program is very simple and consists of only a few lines.
PicBasic program for this example is given in Figure 5. 148.
ROBOT CONTROL
In this project a mobile robot is controlled. The robot has two side wheels and
a back caster wheel. Side wheels are connected to servomotors as follows:
Left wheel RBO
Right wheel RBI
In this project the robot moves as follows:
Move the robot forward for 4 seconds
Wait for 5 seconds
Move the robot backward for 3 seconds
Stop
A PIC16F84 type microcontroller is used with a 4 MHz crystal
Author:
Dogan Ibrahim
Date:
January, 2005
Compiler:
PicBasic
File:
SERVO LB AS
Modifications
Figure 5.148 (Continued)
354 PIC BASIC Projects
' Symbols
Symbol PORTB = $06
Symbol TRISB = $86
Symbol J = BO
POKE TRISB,
' PORTB address
' TRISB address
' PORTB is output
' Move the robot forward for 4 seconds
FORJ= 1TO 174
PULSOUT 0, 170
PULSOUT 1, 130
PAUSE 20
NEXT
' Wait for 5 seconds
PAUSE 5000
' Move the robot backward for 3 seconds
FORJ = lTO 130
PULSOUT 0,130
PULSOUT 1, 170
PAUSE 20
NEXT J
END ' End of program
Figure 5.148 PicBasic program for Example 1
Measuring the speed of the robot
The speed of the robot can easily be measured by moving it for a known amount of time and meas-
uring the distance moved during this time. The speed is then given by
Speed = distance/time
In this project the robot moved forward for 10 s and the distance moved was 210 cm. Thus, the
speed of the robot is 210/10 = 21 cm/s.
PicBasic and PicBasic Pro projects 355
Once we know the speed, we can move the robot forward or backward by any required amount.
For example, to move the robot forward by 85 cm, the required time is approximately given by
Time = distance/speed = 85/21 = 4
Thus, the servomotors should be operated for 4 s. The value of loop-count M is then approxi-
mately given by
M = 4000/23 = 174
The required PicBasic code is
FOR J = 1 TO 174
PULSOUT 0, 170
PULSOUT 1, 130
PULSOUT 20
NEXT J
Turning left and right
Several techniques can be used to turn the robot left or right. One technique is to stop the servo-
motor on the side where we wish to turn. For example, we can turn right by stopping the right
servo and turning the left servo anti-clockwise.
Another technique of turning a robot smoothly involves rotating both servos in the same direction
and this is the technique we shall be using here. For example,
To turn RIGHT:
To turn LEFT:
Rotate left wheel anti-clockwise
Rotate right wheel anti-clockwise
Rotate left wheel clockwise
Rotate right wheel clockwise
The problem here is how many pulses to send to the servomotors so that the robot turns a com-
plete 90° angle. This is something which can be found by trial and error.
The following PicBasic code rotates the robot right where the angle of rotation depends on
variable R:
Turn_right:
FOR J = 1 TO R
PULSOUT 0, 170 ' Left wheel anti-clockwise
356 PIC BASIC Projects
PULSOUT 1, 170 ' Right wheel anti-clockwise
PAUSE 20 'Wait 20 ms
NEXT/
Similarly, the following code rotates the robot left where the angle of rotation depends on variable R:
Turn_left:
FOR J = ITOR
PULSOUT 0, 130 ' Left wheel clockwise
PULSOUT 1, 130 ' Right wheel clockwise
PAUSE 20 'Wait 20 ms
NEXT J
It was found by experimentation that when R [r5] is equal to 13 the robot turns by about 90°. An
example is given below.
Example 2
A mobile robot is controlled with two servomotors as shown in Figure 5. 146, and a pen is attached
to the front of the robot with the tip of the pen touching the floor. Write a PicBasic program which
will move the robot as follows:
Move the robot forward for 5 s
Wait for 2 s
Turn right
Move the robot forward for 3 s
Stop
Solution 2
The first action is to move the robot forward for 5 s. Thus, the value of M is
M= 5000/23 = 217
Then the robot is required to stop for 2 s and then turn right and move backward for 3 s. The value
of M for this movement is
M= 3000/23 = 130
PicBasic program for this example is given in Figure 5. 149.
PicBasic and PicBasic Pro projects 357
ROBOT CONTROL
In this project a mobile robot is controlled. The robot has two side wheels and
a back caster wheel. Side wheels are connected to servomotors as follows:
Left wheel RBO
Right wheel RBI
In this project the robot moves as follows:
Move the robot forward for 4 seconds
Wait for 2 seconds
Turn right
Move the robot forward for 3 seconds
Stop
A PIC16F84 type microcontroller is used with a 4 MHz crystal
Author:
Dogan Ibrahim
Date:
January, 2005
Compiler:
PicBasic
File:
SERV02.BAS
Modifications
Symbols
Symbol PORTB = $06 ' PORTB address
Symbol TRISB = $86 ' TRISB address
Symbol J = BO
POKE TRISB, ' PORTB is output
Figure 5.149 (Continued)
358 PIC BASIC Projects
' Move the robot forward for 4 seconds
FORJ= 1 TO 217
PULSOUT 0, 170
PULSOUT 1, 130
PAUSE 20
NEXT J
' Wait for 2 seconds
PAUSE 2000
' Turn right
FORJ= 1TO 13
PULSOUT 0, 170
PULSOUT 1, 170
PAUSE 20
NEXT J
' Move the robot forward for 3 seconds
FORJ= 1TO 130
PULSOUT 0, 170
PULSOUT 1, 130
PAUSE 20
NEXT J
END ' End of program
Figure 5.149 PicBasic program for Example 2
About the CDROM
The CDROM accompanying this book contains: the Demo version of the PicBasic Pro compiler,
source files (.BAS) and object files (.HEX) of all the projects in the book, all the figures and the
tables used in the book.
The files on the CDROM are organised in the following folders:
DEMO
PROJECT_SOURCES
PROJECT_OBJECTS
FIGURES
TABLES
PicBasic Pro Demo application
Project source files (.BAS)
Project object files (.HEX)
All the figures used in the book
All the tables used in the book
This page intentionally left blank
Index
Note: Page numbers in italics refer to figures and tables.
4-digit external interrupt- driven event
counter, 236^10
4-digit LED display with serial driver:
counter project, 210-26
counter project with leading zeroes
blanked, 227-35
4-digit timer interrupt-driven chronograph,
241-7
7-segment LED DICE, 182-8
7-segment LED display counter, 172-81
8-bit microcontroller, 22
12-bit instruction word:
PIC12C508, 15-16
PIC16C5X, 16
14-bit instruction word:
PIC16C554, 17
PIC16F73,20
PIC16F84, 17, 18
PIC16F627, 18,79
PIC16F676, 18,20
PIC16F877, 17-18,79
16-bit instruction word, 21
A/D converter registers, 30-4
ADCIN command, 108
ADCON0 register, 31-4
bit definition, 33
ADCON1 register, 31,34
bit definition, 35
Altair, 1
Analogue comparator, 10
Analogue-to-digital (A/D) converter, 8-9, 30
Arithmetic operators, in PicBasic Pro:
ABS, 106
COS, 106
DCD, 107
DIG, 107
NCD, 107
shift, 105-6
SIN, 107
SQR, 107
Asynchronous interrupts, 41
Binary counting LEDs, 148-51
Bit definition:
ADCON0 register, 33
ADCON1 register, 35
INTCON register, 32
OPTION_REG register, 24
T1CON register, 30
T2CON register, 31
Boe Bot, 348
BRANCH command, 87
BRANCHL command, 108
Brown-out detector, 8
Bundled development systems:
advantages, 69
developer's bundle, 69
LAB-X1 bundle, with serial
programmer, 70
PicBasic compiler bundle, 69-70
Busicom, 1
BUTTON command, 87-8
Button input, 46
active low-button input, 46
active high-button input, 46
transistor input, 47
CALL command, 88
Car park control system, 248-59
CLEAR command, 108
CLEARWDT command, 108
362 Index
Clock, 7
CodeDesigner Lite, 62-4
Complex flashing LED, 138-41
Complex Instruction Set Computer (CISC), 1 1
CON keyword, 103
Configuration word, 42
COUNT command, 108
Crystal oscillator, 36-7
Current sink/source capability, 10
DATA command, 108
Data memory, 4, 22
DEFINE command, 104
Developer's bundle, 69
Development tools, microcontroller project
development cycle:
ICE, 77-8
simulator, 77
DISABLE command, 124
DOS edit, 61
DTMFOUT command, 109
Dual 7-segment LED display, 189-97
Dual 7-segment LED display counter,
198-203
Dual 7-segment LED event counter, 204-9
EasyPIC 2 development system, 72-3
EEPROM, 6
flash, 6
data memory, 9
EEPROM command, 90-1
EEPROM data memory, 9
Electronic organ, 331-6
musical tones, improvement, 336
Embedded controller see Microcontroller
ENABLE command, 124
END command, 9 1
EPIC Plus programmer, 50-1, 57
EPROM, 6
Experimenter board:
EasyPIC 2 development system, 72-3
LAB -XI experimenter board, 71
PIC microcontroller training and
development kit, 72
FED programmer, 50, 57
Flash EEPROM, 6
Flashing LED warning lights, 142-3
FOR.. .NEXT command, 88-9
FREQOUT command, 109
Gang programmer, 51-2, 52
General Purpose Register (GPR), 22
GOSUB... RETURN command, 89
GOTO command, 89
Hardware tools, required:
minimum support components, in PIC
microcontroller, 53-7
PC, 49-50
PIC microcontroller, 53-7
PIC microcontroller programmer device,
50-2
power supply, in PIC microcontroller
circuit, 58-60
solderless breadboard, 52-3
Harvard architecture, 1 1
HD44780 LCD module, 1 15-16
pin configuration, 775
HIGH command, 91
High current load interface, 44
HPWM command, 109
HSERIN command, 110
HSERIN2 command, 1 10
HSEROUT command, 110
HSEROUT2 command, 110
I/O interface, 42
button input, 46-7
high current load interface, 44
LED interface, 43
relay interface, 44-5
I/O registers, 23-6
port data register, 23, 25
port direction control register, 23, 24, 25
I2CIN command, 91-2
I2COUT command, 93
IF... THEN command, 89-90
Index 363
IF... THEN... ELSE command, 110-11
conditional jump, 110
conditional statement, 110
multiple statements, 110
In Circuit Debugger (ICD), 64, 78
In Circuit Emulator (ICE), 77-8
In-circuit serial programming (ISP), 21
INPUT command, 93
Instruction cycle, 7
INTCON register, 29-30, 41
bit definition, 32
Internal oscillator, 38-9
Interrupt Service Routine (ISR), 8, 124, 125
Interrupt vector address, 8
Interrupts, 8, 41-2, 124-5
asynchronous, 41
Global Interrupt Enable (GIE), 32, 41
synchronous, 41
LAB-X1 bundle, with serial programmer, 70
LAB -XI experimenter board, 71
LCD commands, 118
LCD connection, to microcontroller, 1 16-19
LCD drivers, 9
LCD interface, 113
character table, 119
parallel LCDs, 114-20
serial LCDs, 120-4
LCD-based chronometer, 280-7
LCD-based clock:
with hours-minutes-seconds display,
271-9
LCD-based thermometer using A/D
converter, 300-5
LCD-based voltmeter using A/D converter,
288-99
LCDOUT command, 117-18
LED DICE, 165-71
LED interface, 43
Left scrolling LEDs, 152-5
LOOKDOWN command, 93
LOOKUP command, 93-4
LOW command, 94
Low power operation, 10
Mathematical and logical operations, in
PicBasic, 85-6
Memory, 4
Microcode Studio, 64-5
ICD, 64
Microcomputer, 1, 2
Microcomputer system, 1
see also microcontroller
Microcontroller, 1, 2, 4
architecture, 4, 5, 11
features, 6-10
PIC microcontroller project, steps, 2
systems, 1, 2-6
Microcontroller architecture, 4, 5, 11
CISC, 11
RISC, 11
Microcontroller features, 6
A/D converter, 8-9
analogue comparator, 10
brown-out detector, 8
clock, 7
current sink/source capability, 10
EEPROM data memory, 9
interrupts, 8
LCD drivers, 9
low power operation, 10
power-on reset, 10
real-time clock, 10
reset input, 8
serial I/O, 9
sleep mode, 10
supply voltage, 7
timers, 7
watchdog, 7-8
Microcontroller pin configuration, 16, 18,
19, 20
Microcontroller systems, 1, 2-6
EEPROM, 6
EPROM, 6
flash EEPROM, 6
RAM, 5
ROM, 6
Microprocessor, 1 , 2
comparison with microcontroller, 2
364 Index
Minimum support components, in PIC
microcontroller:
capacitor, 54
reset circuitry, 53, 55-7
resonator, 55, 56
timing components, 53-4, 54-5
NAP command, 94
ON INTERRUPT GOTO command, 124
One time programmable (OTP), 6
OPTION register, 23
OPTION_REG register, 23
OPTION_REG register, 23
bit definition, 24
ORG, 22
OSCCAL register, 38-9
Oscillator circuit, 34
crystal oscillator, 36-7
internal oscillator, 38-9
RC oscillator, 37-8
resonator oscillator, 37
OUTPUT command, 94
Parallel LCDs, 114
HD44780 LCD module, 1 15-16
LCD connection, to microcontroller,
116-19
PAUSE command, 95
PAUSES statement, 1 1 1
PC, 49-50
PEEK command, 25-6, 95
PIC microcontroller, 53
configuration word, 42
data memory, 22
factors, for microcontroller selection, 14-15
features, 14
I/O interface, 42-7
interrupts, 41-2
oscillator circuit, 34-9
program memory, 21-2
programmer device, 50-2
reset circuit, 40, 53, 55-7
RFM, 22
specifications, 13
timing components, 53-4, 54-5
training and development kit, 72
PIC microcontroller family, 13
12-bit instruction word, 15-16
14-bit instruction word, 17-20
16-bit instruction word, 21
microcontroller, features, 21
PIC microcontroller programmer device:
EPIC Plus programmer, 50-1, 57
FED programmer, 50, 57
gang programmer, 51-2, 52
PIC microcontroller project development:
bundled development system, 69-70
development tools, 77-8
example, 73-7
experimenter boards, 71-3
hardware tools, required, 49-60
software tools, required, 60-9
PIC microcontroller training and
development kit, 72
PIC microcontroller-based project
development:
OTP, 6
steps, 2
PIC microcontroller-based projects see
PicBasic projects; PicBasic Projects
PIC12C508, 15-16
pin configuration, 16
PIC16C554, 17
PIC16C5X, 16
PIC16C56 microcontroller, pin
configuration, 16
PIC16F73, 20
pin configuration, 20
PIC16F84, 17
pin configuration, 18
pin description, 18
PIC16F627, 18
pin configuration, 19
PIC 16F676, 18,20
pin configuration, 20
PIC16F877, 17-18
pin configuration, 19
Index 365
PicBasic compiler, 65-7
bundle, 69-70
PicBasic compiler bundle, 69-70
PicBasic language, 80
ASCII values, 84
comments, program, 84
line labels, 84
mathematical and logical operations, 85-6
multi- statement lines, 84-5
numerical values, specification, 84
program flow control commands, 86-90
string constants, 84
symbol, 83
variables, 80-3
PicBasic Pro compiler, 65-7
usage, in project development, 75-7
PicBasic Pro language, 101
arithmetic operators, 105-7
commands, 107-13
comments, 103
constants, 103
INCLUDE, 104
line extension, 104
multi- statement lines, 103
ports and registers, assessment, 104-5
variables, 102-3
PicBasic Pro project see PicBasic Pro
programs
PicBasic Pro programming, 80
language, 101-13
comparison with PicBasic, 81
structure, recommended, 125-6
using servomotors, in microcontroller-
based projects, 128-9
using stepping motors, in microcontroller-
based projects, 126-8
PicBasic programming, 80
language, 80
comparison with PicBasic Pro, 81
structure, recommended, 101
using servomotors, in microcontroller-
based projects, 128-9
using stepping motors, in microcontroller-
based projects, 126-8
PicBasic Pro programs:
4-digit external interrupt-driven event
counter, 237, 237-40
4-digit LED display with serial driver -
counter project, 275, 223-6
4-digit LED display with serial driver -
counter project with leading zeroes
blanked, 227, 232-5
4-digit timer interrupt-driven chronograph,
242, 243-7
7-segment LED DICE, 186-8
7-segment LED display counter, 179-81
binary counting LEDs, 150-1
car park control system, 249, 256-9
complex flashing LED, 138, 141
complex LED warning lights, 142
dual 7-segment LED display, 193, 195-7
dual 7-segment LED display counter, 799,
200-3
dual 7-segment LED event counter, 205,
206-9
electronic organ, 332, 333-5
LCD-based chronometer, 281-7
LCD-based clock with
hours-minutes-seconds display, 272-9
LCD-based thermometer using A/D
converter, 302, 303-5
LCD-based voltmeter using A/D converter,
290,291-9
LED DICE, 169-71
left scrolling LEDs, 154-5
programmable thermometer with RS232
serial output, 319, 324-9
right scrolling LEDs, 158-9
right-left scrolling LEDs, 163-4
seconds counter with LCD display, 262-4
serial LCD-based thermometer with
external EEPROM memory, 309-14
simple flashing LED, 135
turning on odd numbered LEDs, 146-7
unipolar stepping motor control, 339,
341-3
unipolar stepping motor control using
UCN5804C, 345, 347
366 Index
PicBasic programs:
4-digit LED display with serial driver -
counter project, 215-23
4-digit LED display with serial driver -
counter project with leading zeroes
blanked, 227, 228-32
7-segment LED DICE, 184-6
7-segment LED display counter, 111 -9
binary counting LEDs, 149-50
car park control system, 249, 250-5
complex flashing LED, 138, 139-40
dual 7-segment LED display, 191-5
flashing LED warning lights, 142
LED DICE, 166-9
left scrolling LEDs, 153-4
programmable thermometer with RS232
serial output, 319-24
right scrolling LEDs, 157-8
right-left scrolling LEDs, 161-3
seconds counter with LCD display, 262,
264-70
simple flashing LED, 133-4
turning on odd numbered LEDs, 145-6
unipolar stepping motor control, 339^-1
unipolar stepping motor control using
UCN5804C, 344, 346
PicBasic projects see PicBasic programs
PicBasic variables, 80
bit, 80-1
byte, 80
Dirs, 82-3, 83
Pins, 82, 83
Port, 83
word, 80
POKE command, 25-6, 95
Port data register, 23, 25
Port direction control register, 23, 24, 25
Ports and registers, assessment:
in PicBasic Pro, 104-5
POT command, 95-6
Power supply, in PIC microcontroller circuit,
58-60
Power-on reset, 10
Program memory, 4, 21-2
Programmable thermometer with RS232
serial output, 315-30
Programmer device software, 67-9
Project development, example:
circuit construction, 74-5
circuit design, 73
components, requirement, 73-4
PicBasic Pro compiler, 75-7
writing program, 75
PULSIN command, 96
PULSOUT command, 96
PWM command, 96-7
RAM, 5
see Data memory
RANDOM command, 97
RC oscillator, 37-8
READ command, 97
Real-time clock, 10
Reduced Instruction Set Computer (RISC),
11
Register File Map (RFM), 22
GPR, 22
SFR, 22, 23
Relay interface, 44-5
REM keyword, 84, 103
REPEAT... UNTIL command, 1 1 1
Reset circuit, 40
Reset input, 8
Resonator oscillator, 37
RESUME command, 124
REVERSE command, 97-8
Right scrolling LEDs, 156-9
Right-left scrolling LEDs, 160^1
ROM, 6
Seconds counter with LCD display, 260-70
SELECT. .CASE command, 111-12
Serial I/O, 9
Serial LCD-based thermometer:
with external EEPROM memory, 306-14
Serial LCDs, 114, 120
ILM-216 LCD control codes, 121-3
ILM-216 LCD pin configuration, 121
Index 367
SERIN command, 98-9
SEROUT command, 99-100
Servomotor, usage:
in microcontroller-based projects,
128-9
Servomotor-based mobile robot control,
348-58
backward movement, 351
forward movement, 35 1
left/right turning, 355-6
robot speed, measurement, 354-5
servomotor, operation, 349-51
time, for robot movement, 351-2
SHIFTIN command, 112
SHIFTOUT command, 113
Simple flashing LED, 132-7
microcontroller, usage, 136-7
Simulator:
disadvantage, 77
SLEEP command, 100
Sleep mode, 10
Software tools, required:
PicBasic compiler, 65-7
PicBasic Pro compiler, 65-7
programmer device software, 67-9
text editor, 60-5
Solderless breadboard, 52-3
SOUND command, 100
Special Function Register (SFR), 22
A/D converter register, 30-4
I/O register, 23-6
INTCON register, 29-30, 41
OPTION register, 23
timer register, 26-9
Stepping motor, usage:
in microcontroller-based projects, 126-8
Supply voltage, 7
SWAP command, 113
Symbol, 83
Synchronous interrupts, 41
T1CON register, 29
bit definition, 30
T2CON register, 29
bit definition, 31
Text editor, 60
CodeDesigner Lite, 62-4
DOS edit, 61
Microcode Studio, 64-5
WINDOWS notepad, 61-2
Timer registers, 26
TMR0, 26, 26-8
TMR1,29
TMR2, 29
watchdog, 26, 26-8
Timers, 7
TMR0 register, 26, 26-8
overflow time, 27-8, 28
TMR1 register, 29
TMR2 register, 29
TOGGLE command, 100-1
TRIS register, 24-5
Turning on odd numbered LEDs, 144-7
Unipolar stepping motor control, 337^-3
using UCN5804B, 344-7
Von Neumann architecture, 1 1
Watchdog, 7-8, 26, 26-8
Web sites, links, 78-9
WHILE... WEND command, 113
WINDOWS notepad, 61-2
WRITE command, 101
ZIF socket, 50, 51
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