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Chapter 1 - Introduction to Microprocessors

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CHAPTER 1

I ntroduction to Microcontrollers

Introduction

History

Microcontrollers versus microprocessors

1.1 Memory unit

1.2 Central processing unit

1.3 Buses

1.4 Input-output unit

1.5 Serial communication

1.6 Timer unit

1.7 Watchdog

1.8 Analog-digital converter

1.9 Program

I ntroduction

Circumstances that we find ourselves in today in the field of microcontrollers had their beginnings
in the development of technology of integrated circuits. This development has made it possible to
store hundreds of thousands of transistors into one chip. That was a prerequisite for production of
microprocessors , and the first computers were made by adding external peripherals such as
memory, input-output lines, timers and other. Further increasing of the volume of the package
resulted in creation of integrated circuits. These integrated circuits contained both processor and
peripherals. That is how the first chip containing a microcomputer , or what would later be known
as a microcontroller came about.

History

It is year 1969, and a team of Japanese engineers from the BUSICOM company arrives to United

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Chapter 1 - Introduction to Microprocessors

States with a request that a few integrated circuits for calculators be made using their projects.
The proposition was made to INTEL, and Marcian Hoff was responsible for the project. Since he
was the one who has had experience in working with a computer (PC) PDP8, it occured to him to
suggest a fundamentally different solution instead of the suggested construction. This solution
presumed that the function of the integrated circuit is determined by a program stored in it. That
meant that configuration would be more simple, but that it would require far more memory than
the project that was proposed by Japanese engineers would require. After a while, though
Japanese engineers tried finding an easier solution, Marcian's idea won, and the first
microprocessor was born. In transforming an idea into a ready made product , Frederico Faggin
was a major help to INTEL. He transferred to INTEL, and in only 9 months had succeeded in
making a product from its first conception. INTEL obtained the rights to sell this integral block in
1971. First, they bought the license from the BUSICOM company who had no idea what treasure
they had. During that year, there appeared on the market a microprocessor called 4004. That was
the first 4-bit microprocessor with the speed of 6 000 operations per second. Not long after that,
American company CTC requested from INTEL and Texas Instruments to make an 8- bit
microprocessor for use in terminals. Even though CTC gave up this idea in the end, Intel and
Texas Instruments kept working on the microprocessor and in April of 1972, first 8-bit
microprocessor appears on the market under a name 8008. It could address 16Kb of memory, and
it had 45 instructions and the speed of 300 000 operations per second. That microprocessor was
the predecessor of all today's microprocessors. Intel kept their developments up in April of 1974,
and they put on the market the 8-bit processor under a name 8080 which could address 64Kb of
memory, and which had 75 instructions, and the price began at $360.

In another American company Motorola, they realized quickly what was happening, so they put
out on the market an 8-bit microprocessor 6800. Chief constructor was Chuck Peddle, and along
with the processor itself, Motorola was the first company to make other peripherals such as 6820
and 6850. At that time many companies recognized greater importance of microprocessors and
began their own developments. Chuck Peddle leaves Motorola to join MOS Technology and keeps
working intensively on developing microprocessors.

At the WESCON exhibit in United States in 1975, a critical event took place in the history of
microprocessors. The MOS Technology announced it was marketing microprocessors 6501 and
6502 at $25 each, which buyers could purchase immediately. This was so sensational that many
thought it was some kind of a scam, considering that competitors were selling 8080 and 6800 at
$179 each. As an answer to its competitor, both Intel and Motorola lower their prices on the first
day of the exhibit down to $69.95 per microprocessor. Motorola quickly brings suit against MOS
Technology and Chuck Peddle for copying the protected 6800. MOS Technology stops making
6501, but keeps producing 6502. The 6502 is a 8-bit microprocessor with 56 instructions and a
capability of directly addressing 64Kb of memory. Due to low cost , 6502 becomes very popular,
so it is installed into computers such as: KIM-1, Apple I, Apple II, Atari, Comodore, Acorn, Oric,
Galeb, Orao, Ultra, and many others. Soon appear several makers of 6502 (Rockwell, Sznertek,
GTE, NCR, Ricoh, and Comodore takes over MOS Technology) which was at the time of its
prosperity sold at a rate of 15 million processors a year!

Others were not giving up though. Frederico Faggin leaves Intel, and starts his own Zilog Inc.
In 1976 Zilog announces the Z80. During the making of this microprocessor, Faggin makes a
pivotal decision. Knowing that a great deal of programs have been already developed for 8080,
Faggin realizes that many will stay faithful to that microprocessor because of great expenditure
which redoing of all of the programs would result in. Thus he decides that a new processor must
be compatible with 8080, or that it must be capable of performing all of the programs which had
already been written for 8080. Beside these characteristics, many new ones have been added, so

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Chapter 1 - Introduction to Microprocessors

that Z80 was a very powerful microprocessor in its time. It could address directly 64 Kb of
memory, it had 176 instructions, a large number of registers, a built in option for refreshing the
dynamic RAM memory, single-supply, greater speed of work etc. Z80 was a great success and
everybody converted from 8080 to Z80. It can be said that Z80 was without a doubt commercially
most successful 8-bit microprocessor of that time. Besides Zilog, other new manufacturers like
Mostek, NEC, SHARP, and SGS also appear. Z80 was the heart of many computers like Spectrum,
Partner, TRS703, Z-3 and Galaxy here at home.

In 1976, Intel comes up with an improved version of 8-bit microprocessor named 8085. However,
Z80 was so much better that Intel soon lost the battle. Even though a few more processors
appeared on the market (6809, 2650, SC/MP etc.), everything was actually already decided. There
weren't any more great improvements to make manufacturers convert to something new, so 6502
and Z80 along with 6800 remained as main representatives of the 8-bit microprocessors of that
time.

Microcontrollers versus Microprocessors

Microcontroller differs from a microprocessor in many ways. First and the most important is its
functionality. In order for a microprocessor to be used, other components such as memory, or
components for receiving and sending data must be added to it. In short that means that
microprocessor is the very heart of the computer. On the other hand, microcontroller is designed
to be all of that in one. No other external components are needed for its application because all
necessary peripherals are already built into it. Thus, we save the time and space needed to
construct devices.

1.1 Memory unit

Memory is part of the microcontroller whose function is to store data.

The easiest way to explain it is to describe it as one big closet with lots of drawers. If we suppose
that we marked the drawers is such a way that they can not be confused, any of their contents
will then be easily accessible. It is enough to know the designation of the drawer and so its
contents will be known to us for sure.

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mem. location

mem. location 1

mem. location 2

Addresses

Data

mem. location 14

mem. location 15

Example of a simplified model
of a memory unit. For a
specific input we get a
corresponding output. Line
R/W determines whether we
are reading from or writing to
memory.

R/W

Memory components are exactly like that. For a certain input we get the contents of a certain
addressed memory location and that's all. Two new concepts are brought to us: addressing and
memory location. Memory consists of all memory locations, and addressing is nothing but
selecting one of them. This means that we need to select the desired memory location on one end,
and on the other end we need to wait for the contents of that location. Beside reading from a
memory location, memory must also provide for writing onto it. This is done by supplying an
additional line called control line. We will designate this line as R/W (read/write). Control line is
used in the following way: if r/w=l, reading is done, and if opposite is true then writing is done on
the memory location. Memory is the first element, and we need a few others in order for our
microcontroller to work.

1.2 Central Processing Unit

Let's add 3 more memory locations to a specific block that will have a built in capability to
multiply, divide, subtract, and move its contents from one memory location onto another. The part
we just added in is called "central processing unit" (CPU). Its memory locations are called
registers.

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Chapter 1 - Introduction to Microprocessors

Addresses

Example of a simplified centra
processing unit with three
registers

Data

ines

CPU

Registers are therefore memory locations whose role is to help with performing various
mathematical operations or any other operations with data wherever data can be found. Lets look
at the current situation. We have two independent entities (memory and CPU) which are
interconnected, and thus any exchange of data is hindered, as well as its functionality. If, for
example, we wish to add the contents of two memory locations and return the result again back to
memory, we will need a connection between memory and CPU. Simply stated, we must have some
"way" through which data goes from one block to another.

1.3 Bus

That "way" is called "bus". Physically, it represents a group of 8, 16, or more wires
There are two types of buses: address and data bus. The first one consists of as many lines as the
amount of memory we wish to address, and the other one is as wide as data, in our case 8 bits or
the connection line. First one serves to transmit address from CPU memory, and the second to
connect all blocks inside the microcontroller.

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Chapter 1 - Introduction to Microprocessors

mem. location

mem. location 1

mem. location 2

MEMORY

mem. location 14

mem. location 15

Connecting memory and central unit
using busses in order to gain on
functionality

Addresses

CPU

As far as functionality, the situation has improved, but a new problem has also appeared: we have
a unit that's capable of working by itself, but which does not have any contact with the outside
world, or with us! In order to remove this deficiency, let's add a block which contains several
memory locations whose one end is connected to the data bus, and the other has connection with
the output lines on the microcontroller which can be seen with the naked eye as pins on the
electronic component.

1.4 I nput-output unit

Those locations we've just added are called "ports". There are several types of ports : input,
output or two-way ports. When working with ports, first of all it is necessary to choose which port
we need to work with, and then to send data to, or take it from the port.

Input
register

Output

Data

I/O Unit

Example of a simplified
input-output unit that
provides communication
with external world

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Chapter 1 - Introduction to Microprocessors

When working with it the port acts like a memory location. Something is simply being written into
or read from it, and it is possible to easily register that on the pins of the microcontroller.

1.5 Serial communication

With this we've added to the already existing unit the possibility of communication with an outside
world. However, this way of communicating has its drawbacks. One of the basic drawbacks is the
number of lines which need to be used in order to transfer data. What if it is being transferred to a
distance of several kilometers? The number of lines times number of kilometers doesn't promise
the economy of the project. It leaves us having to reduce the number of lines though in such a
way that we don't lessen its functionality. Suppose we are working with three lines only, and that
one line is used for sending data, other for receiving, and the third one is used as a reference line
for both the input and the output side. In order for this to work, we need to set the rules of
exchange of data. These rules are called protocol. Protocol is therefore defined in advance so there
wouldn't be any misunderstanding between the sides that are communicating with each other. For
example, if one man is speaking in French, and the other in English, it is highly unlikely that they
will quickly and effectively understand each other. Let's suppose we have the following protocol.
The logical unit "1" is set up on the transmitting line until transfer begins. Once the transfer starts,
we lower the transmission line to logical "0" for a period of time (which we will designate as T), so
the receiving side will know that it is receiving data, and so it will activate its mechanism for
reception. Let's go back now to the transmission side and start putting logic zeros and ones onto
the transmitter line in the order from a bit of the lowest value to a bit of the highest value. Let
each bit stay on line for a time period which is equal to T, and in the end, or after the 8th bit, let
us bring the logical unit "1" back on the line which will mark the end of the transmission of one
data. The protocol we've just described is called in professional literature NRZ (Non-Return to
Zero).

Receiving

transmitter

Data

Serial
unit

Receiver line
Transmitter

Reference line

Serial unit used to send
data, but only from
three lines

As we have separate lines for receiving and sending, it is possible to receive and send data (info.)
at the same time. Block which enables this way of communication is called a serial communication
block. Unlike the parallel transmission, data moves here bit by bit, or in a series of bits which is
where the name serial communication comes from. After the reception of data we need to read it
from the transmitting location and store it in memory as opposed to sending where the process is
reversed. Data goes from memory through the bus to the sending location, and from there to the
receiving unit according to the protocol.

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Chapter 1 - Introduction to Microprocessors

1.6 Timer unit

Now that we have the serial communication down, we can receive, send and process data

Free
counter-

Timer
unit

+- Signa

Timer unit generates signals
in regular time intervals

However, for us to be able to utilize it in industry we need a few more blocks. One of those is the
timer block which is significant to us because it can give us information about time, duration,
protocol etc. The basic unit of the timer is a free counter which is in fact a register whose numeric
value increases in even intervals, so that by taking its value during periods Tl and T2 and on the
basis of their difference we can determine how much time has elapsed. This is a very important
part of the microcontroller whose mastery requires most of our time.

1.7 Watchdog

One more thing requiring our attention is a flawless performance of the microcontroller

during its use. Suppose that as a result of some interference (which often does occur in industry)

our microcontroller stops executing the program, or worse, it starts working incorrectly.

reset

Free
counter

Watchdog

Of course, when this happens with a computer, we simply reset it and it will keep working.
However, there is no reset button we can push on the microcontroller and thus solve our problem
To overcome this obstacle, we need to introduce one more block called watchdog. This block is in
fact another free counter where our program needs to write a zero in every time it executes
correctly. In case that program gets "stuck", zero will not be written in, and counter alone will
reset the microcontroller upon obtaining its maximum value. This will result in running the
program again, and correctly this time around. That is an important element of every program
that needs to be reliable without man's supervision.

1.8 Analog-Digital Converter

As the peripheral signals are substantially different from the ones that microcontroller
can understand (zero and one), they have to be converted into a mode which can be

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comprehended by a microcontroller. This task is performed by a block for analog-digital
conversion or by an AD converter. This block is responsible for converting an information about
some analog value to a binary number and for follow it through to a CPU block so that CPU block
can further process it.

AD register

Data

A/D converter

Analog input

Block for converting
an analogue to a
digital dimension

Thus, the microcontroller is now finished, and all that is left now is to put it into an electronic
component where it will access inner blocks through the pins of this component. The picture below
shows what a microcontroller looks like inside.

Physical configuration of the interior of a microcontroller

Thin lines which lead from the center towards the sides of the microcontroller represent wires
connecting inner blocks with the pins on the housing of the microcontroller. Chart on the following
page represents the center section of a microcontroller.

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Input
Output

Reference

Serial
unit

mem. location

mem. location 1

mem. location 2

MEMORY

mem. location 14

mem. location IS

Free
counter

Timer
unit

it:

iT5
Ci

Addresses

R/W

A/D
converter

AD output

Data

I/O
unit

Control
nes

CPU

ndependent
counter

Watchdog
timer

Microcontroller outline with its basic elements and internal connections

For a real application, a microcontroller alone is not enough. Beside a microcontroller, we need a
program that will execute, and a few more elements which make up a interface logic towards the
elements of regulation (which will be discussed in later chapters).

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Chapter 1 - Introduction to Microprocessors

1.9 Program

Program writing is a special field of work with microcontrollers and is called "programming". Lets
try writing a small program in a language that we will make up ourselves and that everyone will
be able to understand.

START

REGISTERl = MEMORY LOCATION_A
REGISTER2 = MEMORY LOCATION_B
PORTA=REGISTERl + REGISTER2

END

The program adds up the contents of two memory locations, and views their total on port A. The
first line of the program stands for moving the contents of memory location "A" into one of the
registers of central processing unit. As we need the other data as well, we will also move it into
the other register of the central processing unit. The next instruction instructs the central
processing unit to add up the contents of those two registers and send a result obtained to port A,
so that sum of that addition would be visible to the outside world. For a more complex problem,
program that works on its solution will be bigger.

Programming can be done in several languages such as Assembler, C and Basic which are most
commonly used languages. Assembler belongs to lower level languages that are programmed
slowly, but take up the least amount of space in memory and gives the best results where the
speed of program execution is concerned. As it is the most commonly used language in
programming microcontrollers it will be discussed in a later chapter. Programs in C language are
easier to be written, easier to be understood, but are slower in executing from assembler
programs. Basic is the easiest one to learn, and its instructions are nearest a man's way of
reasoning, but like C programming language it is also slower than assembler. In any case, before
you make up your mind about one of these languages you need to consider carefully the demands
for execution speed, for the size of memory and for the amount of time available for its assembly.
After the program is written, we need to install the microcontroller into a device and let it work. In
order to do this we need to add a few more external components necessary for its work. First we
must give life to a microcontroller by connecting it to a supply (voltage needed for operation of all
electronic instruments) and oscillator whose role is similar to the role that heart plays in a human
body. Based on its clocks microcontroller executes instructions of a program. As it receives supply
microcontroller will perform a small check up on itself, look up the beginning of the program and
start executing it. How the device will work depends on many parameters, the most important of
which is the skillfulness of the developer of hardware, and on programmer's expertise in getting
the maximum out of the device with his program.

a Previous Table of Chapter npy1- nanp t

^ page contents overview '^ CAL ^y c r

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Chapter 1 - Introduction to Microprocessors

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PI C microcontroMers M beginne,s,too.>

Authors: Nebojsa Matic and Dragan Andric

fc.H*. J Paperback - 252 pages (May 15, 2000)
$10

Dimension(May. 75achs)s:)Tj /T40 1 Tf 9.871 9.871321.16 18 629.8597 1

*PIC

microcontroller

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Microcontrollers versus microprocessors

1.1 Memory unit

1.2 Central processing unit

1.3 Buses

1.4 Input-output unit

1.5 Serial communication

1.6 Timer unit

1.7 Watchdog

1.8 Analog-digital converter

1.9 Program

CHAPTER II MICROCONTROLLER PIC16F84

Introduction

CISC, RISC

Applications

Clock/ instruction cycle

Pipelining

Meaning of pins

2.1 Clock generator - oscillator

2.2 Reset

2.3 Central processing unit

2.4 Ports

2.5 Memory organization

2.6 Interrupts

2.7 Free timer TMRO

2.8 EEPROM Data memory

CHAPTER 1 1 1 I NSTRUCTI ON SET

Introduction

Instruction set in PIC16Cxx microcontroller family

Data Transfer

Arithmetic and logic

Bit operations

Directing the program flow

Instruction execution period

Word list

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CHAPTER IV ASSEMBLY LANGUAGE PROGRAMMI NG

Introduction

Sample of a written program

Control directives

4.1 define

4.2 include

4.3 constant

4.4 variable

q
q
q
q

4.5 set

4.6 equ

4.7 orq

4.8 end

Conditional instructions

4.9 if

4.10 else

4.11 endif

4.12 while

4.13 endw

4.14 ifdef

4.15 ifndef

Data directives

q 4.16 cblock

q 4.17 endc

q 4.18 db

q 4.19 de

q 4.20 dt

Configurating a directive

q 4.21 CONFIG
q 4.22 Processor

Assembler arithmetic operators

Files created as a result of program translation

Macros

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CHAPTER V MPLAB

Introduction

5.1 Installing the MPLAB program package

5.2 Introduction to MPLAB

5.3 Choosing the development mode

5.4 Designing a project

5.5 Designing new assembler file

5.6 Writing a program

5.7 MPSIM simulator

5.8 Toolbar

CHAPTER VI SAMPLES

Introduction

6.1 Supplying the microcontroller

6.2 Macros used in programs

q Macros WAIT, WAITX
q Macro PRINT

6.3 Samples

LED diodes

Keyboard

Optocoupler

r Optocouplering the input lines

r Optocouplering the output lines
Relays

Generating a sound
Shift registers

r Input shift register

r Output shift register
7-segment Displays (multiplexing)
LCD display
12-bit AD converter

q Serial communication

APPENDIXES

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APPENDI X A I NSTRUCTI ON SET

APPENDIX B NUMERIC SYSTEMS

Introduction

B.l Decimal numeric system

B.2 Binary numeric system

B.3 Hexadecimal numeric system

Conclusion

APPENDIX C GLOSSARY

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Chapter 2 - Microcontroller PIC16F84

Table of
contents

Chapter
overview

Next page ►

CHAPTER 2

Microcontroller PIC16F84

Introduction

CISC, RISC

Applications

Clock/ instruction cycle

Pipelining

Meaning of pins

2.1 Clock generator - oscillator

2.2 Reset

2.3 Central processing unit

2.4 Ports

2.5 Memory organization

2.6 Interrupts

2.7 Free timer TMRO

2.8 EEPROM Data memory

PIC16F84 belongs to a class of 8-bit microcontrollers of RISC architecture. Its general structure
is shown on the following map representing basic blocks.

Program memory (FLASH)- for storing a written program.

Since memory that's made in FLASH technology can be programmed and cleared more than once,

it makes this microcontroller suitable for device development.

EEPROM - data memory that needs to be saved when there is no supply.
It is usually used for storing important data that must not be lost if supply suddenly stops. For
instance, one such data is an assigned temperature in temperature regulators. If during a loss of
supply this data is lost, we would have to make the adjustment once again upon return of supply.
Thus our device looses on self-reliance.

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Chapter 2 - Microcontroller PIC16F84

RAM - data memory used by a program during its execution.

In RAM are stored all inter- results or temporary data that are not crucial to running a device

during a loss of supply.

PORTA and PORTB are physical connections between the microcontroller and the outside world.
Port A has five, and port B eight pins.

FREE Tl MER is an 8-bit register inside a microcontroller that works independently of the
program. On every fourth clock of the oscillator it increments its value until it reaches the
maximum (255), and then it starts counting over again from zero. As we know the exact timing
between each two increments of the timer contents, timer can be used for measuring time which
is very useful with some devices.

CENTRAL PROCESSI NG UNIT has a role of connective element between other blocks in the
microcontroller. It coordinates the work of other blocks and executes the user program.

Free

Data
memory
RAM

counter

Data
memory
EEPROM

CPU

v. J

^ fe.

Program

memon/

FLASH

*. F

^ ^

PORTA

PORTB

PIC16F84 microcontroller outline

Harvard

von-Neumann

d y hi

ri ^ fc

E
m

E
E

O
D.

Data
memory

CPU

*i *

Harvard vs. von Neumann Block Architectures

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Chapter 2 - Microcontroller PIC16F84

CISC, RISC

It has already been said that PIC16F84 has a RISC architecture. This term is often found in
computer literature, and it needs to be explained here in more detail. Harvard architecture is a
newer concept than von-Neumann's. It rose out of the need to speed up the work of a
microcontroller. In Harvard architecture, data bus and address bus are separate. Thus a greater
flow of data is possible through the central processing unit, and of course, a greater speed of
work. Separating a program from data memory makes it further possible for instructions not to
have to be 8-bit words. PIC16F84 uses 14 bits for instructions which allows for all instructions to
be one word instructions. It is also typical for Harvard architecture to have fewer instructions than
von-Neumann's, and to have instructions usually executed in one cycle.

Microcontrollers with Harvard architecture are also called "RISC microcontrollers". RISC stands for
Reduced Instruction Set Computer. Microcontrollers with von-Neumann's architecture are called
'CISC microcontrollers'. Title CISC stands for Complex Instruction Set Computer.
Since PIC16F84 is a RISC microcontroller, that means that it has a reduced set of instructions,
more precisely 35 instructions . (ex. Intel's and Motorola's microcontrollers have over hundred
instructions) All of these instructions are executed in one cycle except for jump and branch
instructions. According to what its maker says, PIC16F84 usually reaches results of 2:1 in code
compression and 4:1 in speed in relation to other 8-bit microcontrollers in its class.

Applications

PIC16F84 perfectly fits many uses, from automotive industries and controlling home appliances to
industrial instruments, remote sensors, electrical doorknobs and safety devices. It is also ideal for
smart cards as well as for battery supplied devices because of its low consumption.
EEPROM memory makes it easier to apply microcontrollers to devices where permanent storage of
various parameters is needed (codes for transmitters, motor speed, receiver frequencies, etc.).
Low cost, low consumption, easy handling and flexibility make PIC16F84 applicable even in areas
where microcontrollers had not previously been considered (example: timer functions, interface
replacement in larger systems, coprocessor applications, etc.).

In System Programmability of this chip (along with using only two pins in data transfer) makes
possible the flexibility of a product, after assembly and testing have been completed. This
capability can be used to create assembly-line production, to store calibration data available only
after final testing, or it can be used to improve programs on finished products.

Clock / instruction cycle

Clock is microcontroller's main starter, and is obtained from an external memory component called
an "oscillator". If we were to compare a microcontroller with a time clock, our "clock" would then
be a ticking sound we hear from the time clock. In that case, oscillator could be compared to a
spring that is wound so time clock can run. Also, force used to wind the time clock can be
compared to an electrical supply.

Clock from the oscillator enters a microcontroller via OSC1 pin where internal circuit of a
microcontroller divides the clock into four even clocks Ql, Q2, Q3, and Q4 which do not overlap.
These four clocks make up one instruction cycle (also called machine cycle) during which one
instruction is executed.

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Execution of instruction starts by calling an instruction that is next in line. Instruction is called
from program memory on every Ql and is written in instruction register on Q4. Decoding and
execution of instruction are done between the next Ql and Q4 cycles. On the following diagram
we can see the relationship between instruction cycle and clock of the oscillator (OSC1) as well as
that of internal clocks Q1-Q4. Program counter (PC) holds information about the address of the
next instruction.

TCYl

TCY2

TCV3

OSC1

Fetch INST (PC)

Ewecute INST(PC-l)

Fetch INST(PC+1)

Execute INST (PC)

Interna
phase
clock

Fetch INST(PC + 2)

Enecute INSTfPC+l)

Clock/ I nstruction Cycle

Pipelining

Instruction cycle consists of cycles Ql, Q2, Q3 and Q4. Cycles of calling and executing instructions
are connected in such a way that in order to make a call, one instruction cycle is needed, and one
more is needed for decoding and execution. However, due to pipelining, each instruction is
effectively executed in one cycle. If instruction causes a change on program counter, and PC
doesn't point to the following but to some other address (which can be the case with jumps or
with calling subprograms), two cycles are needed for executing an instruction. This is so because
instruction must be processed again, but this time from the right address. Cycle of calling begins
with Ql clock, by writing into instruction register (IR). Decoding and executing begins with Q2, Q3
and Q4 clocks.

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Chapter 2 - Microcontroller PIC16F84

I. MOVLW 55h
2- MOVWF PORTB

3. CALL SUB_1

4. BSF PORTA p BIT3(l

5. Instruction @ address SUB 1

TCYO

TOY I

TCY2

TCY3

TCY4

TCYE

Fetch 1

Execute 1

Fetch 2

Execute 2

Fetch 3

Execute 3

ced NOP)

Fetch 4

Flush

UB_1

Fetch SUB_1

Execute SUB_1

Fetch SUB_1 + 1

All instructions are single cycle^ except for any program branches. These take two cycles since the fetch
instructions is "flushed" from the pipeline while the new instruction is being fetched and then executed,

Instruction Pipeline Flow

TCYO reads in instruction MOVLW 55h (it doesn't matter to us what instruction was then

executed, which is why there is no rectangle pictured on the bottom).

TCY1 executes instruction MOVLW 55h and reads in MOVWF PORTB.

TCY2 executes MOVWF PORTB and reads in CALL SUB_1.

TCY3 executes a call of a subprogram CALL SUB_1, and reads in instruction BSF PORTA, BIT3. As

this instruction is not the one we need, or is not the first instruction of a subprogram SUB_1

whose execution is next in order, instruction must be read in again. This is a good example of an

instruction needing more than one cycle.

TCY4 instruction cycle is totally used up for reading in the first instruction from a subprogram at

address SUB_1.

TCY5 executes the first instruction from a subprogram SUB_1 and reads in the next one.

Meaning of pins

PIC16F84 has a total of 18 pins. It is most frequently found in a DIP18 type of housing but can
also be found in SMD housing which is smaller from a DIP. DIP is short for Dual In Package. SMD
is short for Surface Mount Devices suggesting that holes for pins to go through when mounting,
aren't necessary in soldering this type of a component.

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Chapter 2 - Microcontroller PIC16F84

[

RA2
RA3
RA4/T0CKI

MCLR

RA1

RAO

OSC1

OSC2

PIC
V55 16F84 ™

RBOAWT
RBI
RB2
RB3

RB7
RBG
RB5
RB4

□

]

1t-

1-E-

]■

]

Pins on PIC16F84 microcontroller have the following meaning:

P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P

n no.l RA2 Second pin on port A. Has no additional function

n no. 2 RA3 Third pin on port A. Has no additional function.

n no. 3 RA4 Fourth pin on port A. TOCK1 which functions as a timer is also found on this pin

n no. 4 MCLR Reset input and Vpp programming voltage of a microcontroller

n no. 5 Vss Supply, mass.

n no. 6 RBO Zero pin on port B. Interrupt input is an additional function.

n no. 7 RBI First pin on port B. No additional function.

n no. 8 RB2 Second pin on port B. No additional function.

n no. 9 RB3 Third pin on port B. No additional function.

n no. 10 RB4 Fourth pin on port B. No additional function.

n no. 11 RB5 Fifth pin on port B. No additional function.

n no. 12 RB6 Sixth pin on port B. 'Clock' line in program mode.

n no. 13 RB7 Seventh pin on port B. 'Given' line in program mode.

n no. 14 Vdd Positive supply pole.

n no. 15 OSC2 Pin assigned for connecting with an oscillator

n no. 16 OSC1 Pin assigned for connecting with an oscillator

n no. 17 RA2 Second pin on port A. No additional function

n no. 18 RA1 First pin on port A. No additional function.

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2.1 Clock generator - oscillator

Oscillator circuit is used for providing a microcontroller with a clock. Clock is needed so that
microcontroller could execute a program or program instructions.

Types of oscillators

PIC16F84 can work with four different configurations of an oscillator. Since configurations with
crystal oscillator and resistor-condenser (RC) are the ones that are used most frequently, these
are the only ones we will mention here. Microcontroller type with a crystal oscillator has in its
designation XT, and a microcontroller with resistor-condenser pair has a designation RC. This is
important because you need to mention the type of oscillator when buying a microcontroller.

XT Oscillator

Crystal oscillator is kept in metal housing with
two pins where you have written down the
frequency at which crystal oscillates. One
ceramic condenser of 30pF whose other end is
connected to the mass needs to be connected
with each pin.

Oscillator and condensers can be packed in joint
housing with three pins. Such element is called
ceramic resonator and is represented in charts
like the one below. Center pins of the element is
the mass, while end pins are connected with
OSC1 and OSC2 pins on the microcontroller.
When designing a device, the rule is to place an
oscillator nearer a microcontroller, so as to avoid
any interference on lines on which
microcontroller is receiving a clock.

RC Oscillator

[

RA2
RA3
FWWTOCKI

HCLR

RA1

RAO

0SC1

0SC2

PIC

Vss 16F84 Vdd
RBO-ir-TT

]

]■

OSC1

1-E-

}

]

KTALCH

OSC2

Connecting the quartz oscillator to give
clock to a microcontroller

Connecting a resonator onto a
microcontroller

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Chapter 2 - Microcontroller PIC16F84

In applications where great time precision is not necessary, RC oscillator offers additional savings
during purchase. Resonant frequency of RC oscillator depends on supply voltage rate, resistance
R, capacity C and working temperature. It should be mentioned here that resonant frequency is
also influenced by normal variations in process parameters, by tolerance of external R and C
components, etc.

Vdd

Tact/4

-p^Tact

PIC16F84

OSC2/CLKOUT

Note: This pin can be configured as an input ouput pin

Above diagram shows how RC oscillator is connected with PIC16F84. With value of resistor R being
below 2.2k, oscillator can become unstable, or it can even stop the oscillation. With very high
value of R (ex.lM) oscillator becomes very sensitive to noise and humidity. It is recommended
that value of resistor R should be between 3 and 100k. Even though oscillator will work without an
external condenser (C=0pF), condenser above 20pF should still be used for noise and stability. No
matter which oscillator is being used, in order to get a clock that microcontroller works upon, a
clock of the oscillator must be divided by 4. Oscillator clock divided by 4 can also be obtained on
OSC2/CLKOUT pin, and can be used for testing or synchronizing other logical circuits.

Tosc

34!

■ ■ ■ ■ I ■ ■ ■ ■ ■ ■ 1

TCY 1

TCY 2

Tcr 3

Relationship between a clock and a number of instruction cycles

Following a supply, oscillator starts oscillating. Oscillation at first has an uneven period and
amplitude, but after some period of time it becomes stabilized.

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Chapter 2 - Microcontroller PIC16F84

+5V

Voltage

Crystal star up time

Time

Signal of an oscillator clock after receiving the supply on the microcontroller

To prevent such inaccurate clock from influencing microcontroller's performance, we need to keep
the microcontroller in reset state during stabilization of oscillator's clock. Above diagram shows a
typical shape of a signal which microcontroller gets from the quartz oscillator following a supply.

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Chapter 2 - Microcontroller PIC16F84

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Chapter 2 - Microcontroller PIC16F84

Impulse for resetting during supply (power-up) is generated by microcontroller itself when it
detects an increase in supply Vdd (in a range from 1.2V to 1.8V). That impulse lasts 72ms which
is enough time for an oscillator to get stabilized. These 72ms are provided by an internal PWRT
timer which has its own RC oscillator. Microcontroller is in a reset mode as long as PWRT is active,
However, as device is working, problem arises when supply doesn't drop to zero but falls below
the limit that guarantees microcontroller's proper functioning. This is a likely case in practice,
especially in industrial environment where disturbances and instability of supply are an everyday
occurrence. To solve this problem we need to make sure that microcontroller is in a reset state
each time supply falls below the approved limit.

'..'[Ci

Reset signal

72 ms

'..'[Ci

Reset signal

<?2 ms

72 ms

Vffi

Reset signal

72 ms

Examples of supply drop below the limit

If, according to electrical specification, internal reset circuit of a microcontroller can not satisfy the
needs, special electronic components can be used which are capable of generating the desired
reset signal. Beside this function, they can also function in watching over supply voltage. If
voltage drops below specified level, a logical zero appears on MCLR pin which holds the
microcontroller in reset state until voltage is not within limits that guarantee correct performance.

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2.3 Central Processing Unit

Central processing unit (CPU) is the brain of a microcontroller. That part is responsible for finding
and obtaining the right instruction which needs to be executed, for decoding that instruction, and
finally for its execution.

Data Bus

H-l-

>z.

RAM

File registers (f)

zrz

RAM Addr

Instruction reg

Direct Addr

Addr Mux
77 ?"£

Indirect
Addr

FSR re_.

W reg. £

Outline of the central processing unit - CPU

Central processing unit connects all parts of the microcontroller into one whole. Surely, its most
important function is to decode program instructions. When programmer writes a program,
instructions have a clear form like MOVLW 0x20. However, in order for a microcontroller to
understand that, this letter' form of an instruction must be translated into a series of zeros and
ones which is called an 'opcode'. This transition from a letter to binary form is done by translators
such as assembler translator (also known as an assembler). Instruction thus derived from
program memory must be decoded by a central processing unit. We can then select from the table
of all the instructions a set of actions which execute a needed assignment defined in that
instruction. As instructions may within themselves contain assignments which require different
transfers of data from one memory into another, from memory onto ports, or some other
calculations, CPU must be connected with all parts of the microcontroller. This is made possible
through a data bus and an address bus.

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Chapter 2 - Microcontroller PIC16F84

Arithmetic Logic Unit (ALU)

Arithmetic logic unit is responsible for performing operations of adding, subtracting, moving (left
or right within a register) and logic operations. Moving data inside a register is also known as
'shifting'. PIC16F84 contains an 8-bit arithmetic logic unit and 8-bit work registers.

Induction reg

£ STATUS reg. ^

CLP

Arithmetic- logic unit and how it works

In instructions with two operands, ordinarily one operand is in work register (W register), and the
other is one of the registers or a constant. By operand we mean the contents on which some
operation is being done, and a register is any one of the GPR or SFR registers. GPR is short for
'General Purposes Registers', and SFR for 'Special Function Registers'. In instructions with one
operand, an operand is either W register or one of the registers. As an addition in doing operations
in arithmetic and logic, ALU controls status bits (bits found in STATUS register). Execution of some
instructions affects status bits, which depends on the result itself. Depending on which instruction
is being executed, ALU can affect values of Carry (C), Digit Carry (DC), and Zero (Z) bits in
STATUS register.

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Chapter 2 - Microcontroller PIC16F84

ROM

Program
memory

_z_

Program Counter

:_:

8 level stack
(13 bit)

Program Bus

Instruction reg

Instruction
Decoded
Control

LA.
■■T

Timing
Generation

-■L

■■r

OSC2/CLKOUT
OSC1/CLKIN

Direct Addr

Power-up
Timer

Oscillator
Start-up timer

Power-on
Reset

Watchdog
Timer

m m

MCLR Vdd.V:

Data Bus

h-L-

Iz.

RAM

File Registers (f)
7^

RAM Addr

Addr Mux
7T

Indirect
Addr

FSR reg

5 STATUS reg £

MUX

ALU

:_:

W reg

More detailed block outline of PIC16F84 microcontroller

STATUS Register

R/'/V-O

FWW-0

R-1

R/'/V-x

R/W-x

R/'/V-x

| IRP

RP1

RPO

"PD

bit 7

bit o

Legend:

R = Reada

ble

bit

= Writable

bit

U = Unimp

emented bitj

read

as '0'

-n =

at POR

reset

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bit C (Carry) Transfer

Bit that is affected by operations of addition, subtraction and shifting. This bit is set when a

smaller value is being subtracted from a larger one, and is reset when a larger one is subtracted

from a smaller one.

1= transfer occured from the highest resulting bit

0=transfer did not occur

C bit is affected by ADDWF, ADDLW, SUBLW, SUBWF instructions.

bit 1 DC (Digit Carry) DC Transfer

Bit affected by operations of addition and subtraction. Unlike C bit, this bit represents transfer

from the fourth resulting place. It is set when smaller value is subtracted from a larger one, and is

reset when a larger one is subtracted from a smaller one.

l=transfer occured on the fourth bit according to the order of the result

0=transfer did not occur

DC bit is affected by ADDWF, ADDLW, SUBLW, SUBWF instructions.

bit 2 Z (Zero bit) Indication of a zero result

This bit is set when the result of an executed arithmetic logic operation is zero.

l=result equals zero

0=result does not equal zero

bit 3 PD (Power-down bit)

Bit which is set whenever supply is brought to a microcontroller as it starts running, after each
regular reset and after execution of instruction CLRWDT. Instruction SLEEP resets it when
microcontroller falls into low spending/usage regime. Its repeated setting is possible via reset or
by turning the supply on, or off . Setting can be triggered also by a signal on RBO/INT pin, change
on RB port, completion of writing in internal DATA EEPROM, and by a watchdog, too.
l=after supply has been turned on
0= executing SLEEP instruction

bit 4 TO Time-out ; Watchdog overflow.

Bit is set after turning on the supply and execution of CLRWDT and SLEEP instructions. Bit is reset

when watchdog gets to the end signaling that something is not right.

l=overflow did not occur

0=overflow did occur

bit6:5 RPl:RPO (Register Bank Select bits)

These two bits are upper part of the address for direct addressing. Since instructions which

address the memory directly have only seven bits, they need one more bit in order to address all

256 bytes which is how many bytes PIC16F84 has. RP1 bit is not used, but is left for some future

expansions of this microcontroller.

01=first bank

00=zero bank

bit 7 I RP (Register Bank Select bit)

Bit whose role is to be an eighth bit for indirect addressing of internal RAM.

l=bank 2 and 3

0=bank and 1 (from OOh to FFh)

STATUS register contains arithmetic status ALU (C, DC, Z), RESET status (TO, PD) and bits for
selecting of memory bank (IRP, RP1, RPO). Considering that selection of memory bank is
controlled through this register, it has to be present in each bank. Memory bank will be discussed

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in more detail in Memory organization chapter. STATUS register can be a destination for any
instruction, with any other register. If STATUS register is a destination for instructions which affect
Z, DC or C bits, then writing to these three bits is not possible.

OPTION register

R/-/V-1

R/W-1

R/'/V-1

RWV-1

R/W-1

R/'/V-1

RM/-1

R/W-1

RBPU |1J

INTEDG

TOCS

TOSE

PSA

PS2

PS1

PSO

bit 7

bit

Legend:

R = Reada

ble

bit

= Writable

bit

U = Unimp

emented bit^

read

as '0'

-n =

at POR

res

bit 0:2 PSO, PS1, PS2 (Prescaler Rate Select bit)

These three bits define prescaler rate select bit. What a prescaler is and how these bits can affect

the work of a microcontroller will be dealt with in section on TMRO.

Bits

TMRO

W DT

000

ooi

010

Oil

100

101

110

128

256

128

bit 3 PSA (Prescaler Assignment bit)

Bit which assigns prescaler between TMRO and watchdog.

l=prescaler is assigned to watchdog

0=prescaler is assigned to a free timer TMRO

bit 4 TOSE (TMRO Source Edge Select bit)

If it is allowed to trigger TMRO by impulses from the pin RA4/T0CKI, this bit determines whether

this will be to the falling or rising edge of a signal.

l=falling edge

0=rising edge

bit 5 TOCS (TMRO Clock Source Select bit)

This pin enables free timer to increase its state either from internal oscillator on every X A of

oscillator clock, or through external impulses on RA4/T0CKI pin.

l=external impulses

0=1/4 internal clock

bit 6 INTEDG (Interrupt Edge Select bit)

If interrupt is made possible this bit will determine the edge at which an interrupt wi

on pin RBO/INT.

l=rising edge

be activated

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Chapter 2 - Microcontroller PIC16F84

0=falling edge

bit 7 RBPU (PORTB Pull-up Enable bit)

This bit turns on and off internal 'pull-up' resistors on port B

1= "pull-up" resistors turned off

0= "pull-up" resistors turned on

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2.4 Ports

Port refers to a group of pins on a microcontroller which can be accessed simultaneously, or on
which we can set the desired combination of zeros and ones, or read from them an existing status
Physically, port is a register inside a microcontroller which is connected by wires to the pins of a
microcontroller. Ports represent physical connection of Central Processing Unit with an outside
world. Microcontroller uses them in order to watch over or direct other components or devices.
Due to functionality, some pins have twofold roles like PA4/TOCKI for instance, which is
simultaneously the fourth bit of port A and an external input for free counter. Selection of one of
these two pin functions is done in one of the configurational registers. An illustration of this is the
fifth bit TOCS in OPTION register. By selecting one of the functions the other one is disabled.

RA2

RA3

TRISA

PORTA

Relationship between TRI SA and PORTA register

All port pins can be defined as input or output, according to the needs of a device that's being
developed. In order to define a pin as input or output pin, the right combination of zeros and ones
must be written in TRIS register. If at the appropriate place in TRIS register a logical "1" is
written, then that pin is an input pin, and if the opposite is true, it's an output pin. Every port has
its proper TRI S register. Thus, port A has TRI SA at address 85h, and port B has TRI SB at address
86h.

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Chapter 2 - Microcontroller PIC16F84

PORTB

PORTB has 8 pins joined to it. The appropriate register for direction of data is TRISB at address
86h. Setting a bit in TRISB register defines the corresponding port pin as an input pin, and
resetting a bit in TRISB register defines the corresponding port pin as the output pin. Each pin on
PORTB has a weak internal pull-up resistor (resistor which defines a line to logic one) which can be
activated by resetting the seventh bit RBPU in OPTION register. These 'pull-up' resistors are
automatically being turned off when port pin is configured as an output. When a microcontroller is
started, pull-up's are disabled.

Four pins PORTB, RB7:RB4 can cause an interrupt which occurs when their status changes from
logical one into logical zero and the other way around. Only pins configured as input can cause
this interrupt to occur (if any RB7:RB4 pin is configured as an output, an interrupt won't be
generated at the change of status.) This interrupt option along with internal pull-up resistors
makes it easier to solve common problems we find in practice like for instance that of matrix
keyboard. If rows on the keyboard are connected to these pins, each push on a key will then
cause an interrupt. A microcontroller will determine which key is at hand while processing an
interrupt It is not recommended to refer to port B at the same time that interrupt is being
processed.

clrf STATUS ; BankO

clrf PORTB ;PORTB=0

bsf STATUS, RPO ;Bankl

movlu OxOF ; Defining input and output pins

movwf trisb ; Writing to TRISB register

The above example shows how pins 0, 1, 2, and 3 are declared for input, and pins 4, 5, 6, and 7
for output.

PORTA

PORTA has 5 pins joined to it. The corresponding register for data direction is TRISA at address
85h. Like with port B, setting a bit in TRISA register defines also the corresponding port pin as an
input pin, and resetting a bit in TRISA register defines the corresponding port pin as an output pin.
The fifth pin of port A has dual function. On that pin is also situated an external input for timer
TMRO. One of these two options is chosen by setting or resetting the TOCS bit (TMRO Clock Source
Select bit). This pin enables the timer TMRO to increase its status either from internal oscillator or
via external impulses on RA4/T0CKI pin.

bcf STATUS, RPO ; BankO
clrf PORTA ;PORTA=0
bsf STATUS, RPO ;Bankl

movlu OxlF ; Defining input and output pins pi nova

movuf trisa ; Writing to TRISA register

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Chapter 2 - Microcontroller PIC16F84

Example shows how pins 0, 1, 2, 3, and 4 are declared to be input, and pins 5, 6, and 7 to be
output pins.

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2.5 Memory organization

PIC16F84 has two separate memory blocks, one for data and the other for program. EEPROM
memory and GPR registers in RAM memory make up a block for data, and FLASH memory makes
up a program block.

Program memory

Program memory has been realized in FLASH technology which makes it possible to program a
microcontroller many times before it's installed into a device, and even after its installment if
eventual changes in program or process parameters should occur. The size of program memory is
1024 locations with 14 bits width where locations zero and four are reserved for reset and
interrupt vector.

Data memory

Data memory consists of EEPROM and RAM memories. EEPROM memory consists of 64 eight bit
locations whose contents is not lost during an interrupt in supply. EEPROM is not stored directly in
memory space, but is accessed indirectly through EEADR and EEDATA registers. As EEPROM
memory usually serves for storing important parameters (for example, of a given temperature in
temperature regulators) , there is a strict procedure for writing in EEPROM which must be followed
in order to avoid accidental writing. RAM memory for data takes up space on a memory map from
location OxOC to 0x4F which comes to 68 locations. Locations of RAM memory are also called GPR
registers which is short for General Purpose Registers. GPR registers can be accessed regardless of
which bank is selected at the moment.

SFR registers

Registers which take up first 12 locations in banks and 1 are registers of specialized function and
have to do with working with certain blocks of the microcontroller. These are called Special
Function Registers.

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Chapter 2 - Microcontroller PIC16F84

Stack level 1

Stack level 2

Address
bus

Stack level S

— 2; F

Program
counter

PC<12:0> K

z 1

Reset address

Interrupt vector address

Program memory

1024X14

000 Oh

0004h

1FFFh

EEDATA

LU
LU

Address

3Eh
3Fh

Data bus

Address

00h

01h

02h
03h

04h

05h
06h

07h

OSh
09h

OAh
OBh
OCh

4Fh

5 Oh

7Fh

Address

INDF

TMRfl

PCL

STATUS

F5R

PORTA

F-ORTB

EEDftTfl

E&JDR

PC LATH

INTCON

IHDF

OPTION

PCL

STATUS

FSR

TRISA

TRISB

EEGQNi

EECQN2

Ft LATH

INTCOH

68 bajta zajednicke
RAM memorije

GPR Registers

FFh

i"n

BankO
__ +

ankl

1 i

RP1

RPO

STATUS register

Memory organization of microcontroller 16F84

Memory Banks

EEPROM for
data 64XE

Accessing these
locations has the
same result
regardless of the
bank from which
we are making an
access

Unimplemented

memory

locations^

by reading them

we always get

"0"

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Chapter 2 - Microcontroller PIC16F84

Beside this 'linear' division to SFR and GPR registers, memory map is also divided in 'width' (see
preceding map) to two areas called 'banks'. Selecting one of the banks is done via RPO and RP1
bits in STATUS register.

Example:

bcf STATUS, RPO

Instruction BCF resets bit RPO (RP0=0) in STATUS register and thus sets up bank 0.

bsf STATUS, RPO

Instruction BSF sets the bit RPO (RP0=1) in STATUS register and thus sets up bankl.

Usually, groups of instructions that are often in use, are connected into one unit which can easily
be recalled in a program, and whose name has a clear meaning, so called Macros. With their use,
selection between two banks becomes more clear and the program itself more legible.

BANKO macro

Bcf STATUS, RPO /Select memory bank
Endm

BANK1 macro

Bsf STATUS, RPO /Select memory bank 1
Endm

Ik/ Locations OCh - 4Fh are general purpose registers (GPR) which are used as RAM memory.

_■ When locations 8Ch - CFh in Bank 1 are accessed, we actually access the exact same

n locations in Bank 0. In other words , whenever you wish to access one of the GPR

1 registers, there is no need to worry about which bank we are in!

Program Counter

Program counter (PC) is a 13 bit register that contains the address of the instruction being
executed. By its incrementing or change (ex. in case of jumps) microcontroller executes program
instructions one by one.

Stack

PIC16F84 has a 13-bit stack with 8 levels, or in other words, a group of 8 memory locations of 13
bits width with special function. Its basic role is to keep the value of program counter after a jump
from the main program to an address of a subprogram being executed has occured. In order for a
program to know how to go back to the point where it started from, it has to return the value of a
program counter from a stack. When moving from a program to a subprogram, program counter
is being pushed onto a stack (example of this is CALL instruction). When executing instructions
such as RETURN, RETLW or RETFIE which are executed at the end of a subprogram, program
counter is taken from a stack so that program could continue where it stopped before it was
interrupted. These operations of placing on and taking off from a program counter stack are called
PUSH and POP, and are named after instructions which exist on some bigger microcontrollers.

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In System Programming

In order to program a program memory, microcontroller must be set to special working regime by
bringing up MCLR pin to 13.5V, and supply voltage Vdd has to be stabilized between 4.5V to 5.5V.
Program memory can be programmed serially using two 'data/clock' pins which must previously
be separated from device lines, so that errors wouldn't come up during programming.

Addressing modes

RAM memory locations can be accessed directly or indirectly

Direct Addressing

Direct Addressing is done through a 9-bit address. This address is obtained by connecting 7th bit
of direct address of an instruction with two bits (RP1, RPO) from STATUS register as is shown on
the following picture. Any access to SFR registers can be an example of direct addressing.

Bsf STATUS, RPO ; Bankl
movlw OxFF ;w=OxFF

movwf TRISA /address of TRISA register is taken from

/instruction movwf

5th and 6th bit of
STATUS register

RP1 RP2

Seven bits from instruction

Selected side

Selected location

0B
0C

BankO Bankl

Direct addressing

Indirect Addressing

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Indirect unlike direct addressing does not take an address from an instruction but makes it with
the help of IRP bit of STATUS and FSR registers. Addressed location is accessed via INDF register
which in fact holds the address indicated by a FSR. In other words, any instruction which uses
INDF as its register in reality accesses data indicated by a FSR register. Let's say, for instance,
that one general purpose register (GPR) at address OFh contains a value of 20. By writing a value
of OFh in FSR register we will get a register indicator at address OFh, and by reading from I NDF
register, we will get a value of 20, which means that we have read from the first register its value
without accessing it directly (but via FSR and I NDF). It appears that this type of addressing does
not have any advantages over direct addressing, but certain needs do exist during programming
which can be solved smoothly only through indirect addressing.

Seventh bit of
status register

FSR register

Selected side

selected location

BankO Bankl

I ndirect addressing

An example can be sending a set of data via serial communication, working with buffers and
indicators (which will be discussed further in a chapter with examples), or erasing a part of RAM
memory (16 locations) as in the following instance.

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Chapter 2 - Microcontroller PIC16F84

HovIxj OxOC
Hovuf FSR

LOOP cl_f INDF
incf FSR
btfss FSR, 4
goto loop

CONTINUE

initialisation of starting address

; FSR indicates address OxOC

; INDF =

; address = initial address + 1

;are all locations erased

;no, go through a loop again

; yes, continue uith program

Reading data from INDF register when the contents of FSR register is equal to zero returns the
value of zeros, and writing to it results in NOP operation (no operation).

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2.6 I nterrupts

Interrupts are a mechanism of a microcontroller which makes it possible to respond to some
events at the moment when they occur, regardless of what microcontroller is doing at the time.
This is a very important part, because it provides connection between a microcontroller and a real
world which surrounds us. Generally, each interrupt changes the flow of program execution,
interrupts it and after executing an interrupt subprogram (interrupt routine) it continues from that
same point on.

+5"-'

RBO/INT

[

RA2

RA3
RM/TOCKI

Program
execution flow

HCLR p|C

v* 16F84

RBOANT

RBI
RB2
RB3

Continuation
of the norma
program
execution

Point at which an
interrupt o ecu red

Subprogram

where interrupt

is processed

Return to the
main progranr

One of the possible sources of an interrupt and how it affects the main program

Control register of an interrupt is called INTCON and is found at OBh address. Its role is to allow or
disallowed interrupts, and in case they are not allowed, it registers specific interrupt requests
through its own bits.

INTCON Register

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R/'/V-O

RWV-0

R/'/V-O

R/W-0

R/'/V-O

R/W-0

GIE

PEE

TOIE

INTE

RBIE

TOIF

INTF

RBIF

bit 7

bit

Legend:

R = Readable bit W = Writable bit

U = Unimplemented bit, read as '0' -n = Value at POR reset

bit RBI F (RB Port Change Flag bit) Bit which informs about changes on pins 4, 5, 6 and 7 of port

l=at least one pin has changed its status

0=no change occured on any of the pins

bit 1 INTF (INT External Interrupt Flag bit) External interrupt occured.

l=interrupt occured

0=interrupt did not occur

If a rising or falling edge is detected on pin RBO/INT, (which is defined with bit INTEDG in OPTION

interrupt.

bit 2 TOI F (TMRO Overflow I nterrupt Flag bit) Overflow of counter TMRO.

1= counter changed its status with FFh OOh

0=overflow did not occur

Bit must be reset in program in order for an interrupt to be detected.

bit 3 RBIE (RB port change Interrupt Enable bit) Enables interrupts to occur at the change of

status of pins 4, 5, 6, and 7 of port B.

1= enables interrupts at the change of status

0=interrupts disabled at the change of status

If RBIE and RBIF are simultaneously set, an interrupt will occur.

bit 4 INTE (INT External Interrupt Enable bit) Bit which enables external interrupt from pin

RBO/INT.

l=external interrupt enabled

0=external interrupt disabled

If INTE and INTF are set simultaneously, an interrupt will occur.

bit 5 TOIE (TMRO Overflow Interrupt Enable bit) Bit which enables interrupts during counter TMRO

overflow.

l=interrupt enabled

0=interrupt disabled

If TOI E and TOI F are set simultaneously, interrupt will occur.

Bit 6 EEIE (EEPROM Write Complete Interrupt Enable bit) Bit which enables an interrupt at the

end of a writing routine to EEPROM

l=interrupt enabled

0=interrupt disabled

If EEIE and EEIF (which is in EECON1 register) are set simultaneously , an interrupt will occur.

Bit 7 Gl E (Global I nterrupt Enable bit) Bit which allows or disallows all interrupts.
l=all interrupts are enabled

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0=all interrupts are disabled

PIC16F84 has four interrupt sources:

1. Termination of writing data to EEPROM

2. TMRO interrupt caused by timer overflow

3. Interrupt during alteration on RB4, RB5, RB6 and RB7 pins of port B.

4. External interrupt from RBO/INT pin of microcontroller

Generally speaking, each interrupt source has two bits joined to it. One enables interrupts, and
the other detects when interrupts occur. There is one common bit called GIE which can be used to
disallow or enable all interrupts simultaneously. This bit is very useful when writing a program
because it allows for all interrupts to be disabled for a period of time, so that execution of some
important part of a program would not be interrupted. When instruction which resets GIE bit is
executed (GIE=0, all interrupts disallowed), any interrupt that remained unsolved should be
ignored.

EEIF

INTERRUPT

Outline of 16F84 microcontroller interrupt

Interrupts which remained unsolved and are ignored, are processed when GIE bit (GIE=1, all
interrupts allowed) is reset. When interrupt is answered, GIE bit is reset so that any additional
interrupts would be disabled, return address is pushed onto stack and address 0004h is written in
program counter - only after this does replying to an interrupt begin! After interrupt is processed,
bit whose setting caused an interrupt must be reset, or interrupt routine will automatically be
processed over again during a return to the main program.

Keeping the contents of important registers

Only return value of program counter is stored on a stack during an interrupt (by return value of
program counter we mean the address of the instruction which was to be executed, but wasn't
because interrupt occured). Keeping only the value of program counter is often not enough. Some
registers which are already in use in the main program can also be in use in interrupt routine. If

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Chapter 2 - Microcontroller PIC16F84

they were not retained, main program would during a return from an interrupt routine get
completely different values in those registers, which would cause an error in the program. One
example for such a case is contents of the work register W. If we suppose that main program was
using work register W for some of its operations, and if it had stored in it some value that's
important for the following instruction, then an interrupt which occurs before that instruction will
change the value of work register W which will directly influence the main program.

Procedure of recording important registers before going to an interrupt routine is called PUSH,
while the procedure which brings recorded values back, is called POP. PUSH and POP are
instructions with some other microcontrollers (Intel), but are so widely accepted that a whole
operation is named after them. PIC16F84 does not have instructions like PUSH and POP, and they
have to be programmed.

Instruction no. N

Following

instruction after an

interrupt checks

out the value of

work register W

Instruction no. N + 1

Before interrupt

occured, working

value V

W=X

Is W=X ?

Interrupt

subprogram

where interrupt

is processed

has changed

work register

W to Y

W=Y

Return to the
main program

One of the possible cases of errors if saving is not done when going to a subprogram of

an interrupt

Due to simplicity and frequent usage, these parts of the program can be made as macros. The
concept of a Macro is explained in "Program assembly language". In the following example,
contents of W and STATUS registers are stored in W_TEMP and STATUS_TEMP variables prior to
interrupt routine. At the beginning of PUSH routine we need to check presently selected bank
because W_TEMP and STATUS_TEMP are found in bank 0. For exchange of data between these
registers, SWAPF instruction is used instead of MOVF because it does not affect the status of
STATUS register bits.

Example is a program assembler for following steps:

1. Testing the current bank

2. Storing W register regardless of the current bank

3. Storing STATUS register in bank 0.

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4. Executing interrupt routine for interrupt processing (ISR)

5. Restores STATUS register

6. Restores W register

If there are some more variables or registers that need to be stored, then they need to be kept
after storing STATUS register (step 3), and brought back before STATUS register is restored (step
5).

Push

BTFSS STATUS, RPO
GOTO RPOCLEAR
BCF STATUS, RPO
MOVWF W_TEMP
SWAPF STATUS, W
MOVWF STATUS_TEMP
BSF STATU S_TEMP, 1
GOTO ISR_Cod8

RPOCLEAR

MOVWF W_TEMP
SWAPF STATUS, W
MOVWF STATUS TEMP

BankO
Yes

NO, go to BankO
Save W register
W <- STATUS
STATUS_TEMP <- W
RPO(STATUS_TEMP)= 1
Push completed

Save W register
W <- STATUS
STATUS TEMP <- W

ISR Code

(Interrupt subprogram )

Pop

wi-i;

■t- '.ViSGfc -ttHJS is: -ir t llD

■r^u. .-:::: r* (<£*•:,:*"■* r . .jwuiW" '. :ifi

ri'!" 7 ! ■-* ^''T. 1 -' F'"J 51 ( 1

ttjunm^flff*!

^7\'vr\ * \ l ± irfr

; :ET^G"iiiirrrjJi_ffis

r rRiBi j rrg | 3?ff z p^:fffi WF^^s^

The same instance can be realized by using macros, thus getting a more legible program. Macros
that are already defined can be used for writing new macros. Macros BANK1 and BANKO which are
explained in "Memory organization" chapter are used with macros 'push' and 'pop'.

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push macro

movwf W_Temp

swapf W_Tennp J F

BANK1

swapf OPTION.REG.W

m ov wf Opti on_Tem p

BANKO

swapf STATUS.W

m ov wf Stat_Tem p

endm

W_Temp <- W

Swap them

Macro for switching to Bankl

Wo OPTION_REG

Opti on_Tem p <- W

macro for switching to BankO

Wo STATUS

Stat_Temp oW

End of push macro

pop macro

swapf StaLTempjW

movwf STATUS

BANK1

swapf 0|±ion_Temp J W

movwf OPTION_REG

BANKO

swapf W_Temp,W

endm

;W<- Stat_Temp

; STATUS <- W

; Macro for switching to Bankl

; W <- Option_Temp

;OPTION_REG <- W

; Macro for switching to BankO

;Wo W_Temp

; End of a pop macro

External interrupt on RBO/INT pin of microcontroller

External interrupt on RBO/INT pin is triggered by rising signal edge (if bit INTEDG=1 in
OPTION<6> register), or falling edge (if INTEDG=0). When correct signal appears on INT pin,
INTF bit is set in INTCON register. INTF bit (INTC0N<1>) must be reset in interrupt routine, so
that interrupt wouldn't occur again while going back to the main program. This is an important
part of the program which programmer must not forget, or program will constantly go into
interrupt routine. Interrupt can be turned off by resetting INTE control bit (INTCON<4>).

Interrupt during a TMRO counter overflow

Overflow of TMRO counter (with FFh on OOh) will setTOIF (INTCON<2>) bit. This is quite a
significant interrupt because many real problems can be solved using this interrupt. One of the
examples is time measurement. If we know how much time counter needs in order to complete
one cycle from OOh to FFh, then a number of interrupts multiplied by that amount of time will yield
the total of elapsed time. In interrupt routine some variable would be incremented in RAM
memory, value of that variable multiplied by the amount of time the counter needs to count
through a whole cycle, would yield total elapsed time. Interrupt can bi turned on/ off by
setting/ resetting TOIE (INTC0N<5>) bit.

Interrupt during a change on pins 4, 5, 6 and 7 of port B

Change of input signal on PORTB <7:4> sets RBIF (INTCON<0>) bit. Four pins RB7, RB6, RB5
and RB4 of port B, can trigger an interrupt which occurs when status on them changes from logic
one to logic zero, or vice versa. For pins to be sensitive to this change, they must be defined as
input. If any one of them is defined as output, interrupt will not be generated at the change of
status. If they are defined as input, their current state is compared to the old value which was
stored at the last reading from port B. Interrupt can be turned on/off by setting/resetting RBIE bit

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Chapter 2 - Microcontroller PIC16F84

in INTCON register.

Interrupt during

This interrupt is of practical nature only. Since writing to one EEPROM location takes about 10ms
(which is a long time in the notion of a microcontroller), it doesn't pay off to a microcontroller to
wait for writing to end. Thus interrupt mechanism is added which allows the microcontroller to
continue executing the main program, while writing in EEPROM is being done in the background.
When writing is completed, interrupt informs the microcontroller that writing has ended. EEIF bit,
through which this informing is done, is found in EECON1 register. Occurrence of an interrupt can
be disabled by resetting the EEIE bit in INTCON register.

Interrupt initialization

In order to use an interrupt mechanism of a microcontroller, some preparatory tasks need to be
performed. These procedures are in short called "initialization". By initialization we define to what
interrupts the microcontroller will respond, and which ones it will ignore. If we do not set the bit
that allows a certain interrupt, program will not execute an interrupt subprogram. Through this we
can obtain control over interrupt occurrence, which is very useful.

clrf INTCON ; all interrupts disabled

movlu B 1 00010000 ' ; external interrupt only is enabled

bsf INTCON, GIE ; occurrence of interrupts allowed

The above example shows initialization of external interrupt on RBO pin of a microcontroller.
Where we see one being set, that means that interrupt is enabled. Occurrence of other interrupts
is not allowed, and all interrupts together are disallowed until GIE bit is set to one.

The following example shows a typical way of handling interrupts. PIC16F84 has only one location
where the address of an interrupt subprogram is stored. This means that first we need to detect
which interrupt is at hand (if more than one interrupt source is available), and then we can
execute that part of a program which refers to that interrupt.

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Chapter 2 - Microcontroller PIC16F84

org ISR_ADDR

btfsc INTCON, GIE

goto ISR_ADR

PUSH

btfsc INTCON, RBIF

goto ISR_PORTB

btfsc INTCON, INTF

goto ISR_RBO

btfsc INTCON, TO IF

goto ISR_THRO

BANK1

Btfsc EECON1, EEIF

goto ISR_EEPROH

BANKO

I5R_ADDR is interrupt routine address

GIE bit turned off?

no, go back to the beginning

keep the contents of important registers

change on pins 4, 5, 6 and 7 of port B?

jump to that section

external interrupt occured?

jump to that part

overflow of timer THRO?

jump to that section

Bankl because of EECON1

writing to EEPROH completed?

jump to that section

BankO

ISR PORTB

goto END_ISR
ISR RBO

goto END_ISR
ISR THRO

goto END_ISR
ISR EEPROH

; section of code which is processed by an
; interrupt ?

;jump to the exit of an interrupt

; section of code processing an interrupt?

;jump to exit of an interrupt.

; section of code processing an interrupt

;jump to the exit of an interrupt

; section of code which processes an interrupt

goto END_ISR
END_ISR

POP

RETFIE

;jump to an exit from an interrupt.

■

;bringing back the contents of important

; registers

; return and setting of GIE bit

Return from interrupt routine can be accomplished with instructions RETURN, RETLW and
RETFIE. It is recommended that instruction RETFIE be used because that instruction is the
only one which automatically sets the GIE bit which bit allows new interrupts to occur.

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2.7 Free timer TMRO

Timers are ordinarily most complicated parts of a microcontroller, so it is necessary to set aside
more time for their mastering. With their application it is possible to create relations between a
real dimension such as "time" and a variable which represents status of a timer within a
microcontroller. Physically, timer is a register whose value is continually increasing to 255, and
then it starts all over again: 0, 1, 2, 3, 4. ..255 1, 2, 3 etc.

Data Bus

bit 7

TMRO

oooooooo

©®®©©®0®

INTCON

TOIF

...1 23...255...0...1 ...2...255...0...1

Oscillator clock

PS2 PS1 PSO

f Prescater 1:2 > _J

1 * Prescater 1:4 > _J

1 f Prescater 1:8 f _J

OPTION

PS2 PS1 PSO

Relation between the timer TMRO and prescaler

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Chapter 2 - Microcontroller PIC16F84

This incrementing is done in the background of everything a microcontroller does. It is up to
programmer to "think up a way" how he will take advantage of this characteristic for his needs.
One of the ways is increasing some variable on each timer overflow. If we know how much time a
timer needs to make one complete round, then multiplying the value of a variable by that time will
yield the total amount of elapsed time.

PIC16F84 has an 8-bit timer. Number of bits determines what value timer counts to before
starting to count from zero again. In the case of an 8-bit timer, that number is 256. A simplified
scheme of relation between a timer and a prescaler is represented on the previous diagram.
Prescaler is a name for the part of a microcontroller which divides oscillator clock before it will
reach logic that increases timer status. Number which divides a clock is defined through first three
bits in OPTION register. The highest divisor is 256. This actually means that only at every 256th
clock, timer status would increase by one. This provides us with the ability to measure longer
timer periods.

0SC1

u 1 1 \Ji 1 \

JO 1 i

Jt \m

1 1 U^ 1 \m

!■_' 1 \m

n: Ul

1 UI 1 WO 1 \m

IM-: W 1 1

Wi 1 UO 1 W-t : W 1

U^, 1 \m

JO 1 W+:

CLK0UTC2)

[

/ i

TlmerO

FBi

— |—

FFh

oohy

«h :

X v&.

4©

TQIr bit

HI F hit

■

Note: 1. Interrupt flag bitTOIF is examined at the new place at each Ql cycle
3. CLKOUT exists only in RC oscillator mode

Time diagram of interrupt occurence with TMRO timer

After each count up to 255, timer resets its value to zero and starts with a new cycle of counting
to 255. During each transition from 255 to zero, TOIF bit in INTCOM register is set. If interrupts
are allowed to occur, this can be taken advantage of in generating interrupts and in processing
interrupt routine. It is up to programmer to reset TOIF bit in interrupt routine, so that new
interrupt, or new overflow could be detected. Beside the internal oscillator clock, timer status can
also be increased by the external clock on RA4/TOCKI pin. Choosing one of these two options is
done in OPTION register through TOCS bit. If this option of external clock is selected, it is possible
to define the edge of a signal (rising or falling), on which timer will increase its value.

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Chapter 2 - Microcontroller PIC16F84

Metal bulges

Inductive sensor

Motor axle of the
working machine

PIC16F84

RA2

RAS

Interrupt

©{J)®®®®®®

TMRO

Data Bus

Application of TMRO timer to determining a number of full axle turns of the working

machine of a motor

In practice, one of the typical examples that is solved via external clock and a timer is counting
full turns of an axle of some production machine, like transformer winder for instance. Let's wind
four metal screws on the axle of a winder. These four screws will represent metal convexity. Let's
place now the inductive sensor at a distance of 5mm from the head of a screw. Inductive sensor
will generate the falling signal every time the head of the screw is parallel with sensor head. Each
signal will represent one fourth of a full turn, and the sum of all full turns will be found in TMRO
timer. Program can easily read this data from the timer through a data bus.

The following example illustrates how to initialize timer to signal falling edges from external clock
source with a prescaler 1:4. Timer works in "polig" mode.

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Chapter 2 - Microcontroller PIC16F84

clrf THRO ;THRO=0

clrf INTCON interrupts and TOIF=0 disallowed

bsf STATUS, RPO ;Bankl because of OPTION_REG

movlu B'00110001 1 ;prescaler 1:4, falling edge selected external

; clock source and pull up ; selected resistors

;on port B activated
movuf OPTION_REG ;OPTION_REG <- U
T0_OVFL

btfss INTCON, TO IF ; testing overflow bit

goto T0_OVFL ; interrupt has not occured yet , wait

■

; (Part of the program which processes data regarding a number of turns)

■

goto TO OVFL ; waiting for new overflow

The same example can be realized through an interrupt in the following way:

org 0x00 ; reset vector address

goto Start ;beginning of program

org 0x04 ; interrupt vector address

goto T0_OVFL ; beginning of interrupt routine

Start clrf THRO ; THR0=0

clrf INTCON ; Interrupts and T0IF=0 disallowed

bsf STATUS, RP0 ;Bankl because of OPTION_REG

movlw B'00110001 1 ;prescaler 1:4, falling edge, external clock

; source and pull up selected ; resistors on port
;B activated
movwf OPTION_REG ;OPTION_REG <- XJ
bsf INTCON, TOIE ; interrupt on overflow enabled
bsf INTCON, GIE ; interrupts allowed

T0_OVFL

; (Part of the program which is processing data regarding a number of
; turns)

bcf INTCON, TOIF ; interrupt flag is cleared so that next one could be

; detected
retfie ; return from interrupt routine

Prescaler can join either timer TMRO or a watchdog. Watchdog is a mechanism which
microcontroller uses to defend itself against programs getting stuck. As with any other electrical
circuit, so with a microcontroller too can occur failure, or some work impairment. Unfortunately,

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Chapter 2 - Microcontroller PIC16F84

microcontroller also has a component called program where problems can occur as well. When this
happens, microcontroller will stop working and will remain in that state until someone resets it.
Because of this, watchdog mechanism has been introduced. After a certain period of time,
watchdog resets the microcontroller (microcontroller in fact resets itself). Watchdog works on a
simple principle: if timer overflow occurs, microcontroller is reset, and it starts executing a
program all over again. In this way, reset will occur in case of both correct and incorrect
functioning. Next step is preventing reset in case of correct functioning, which is done by writing
zero in WDT register (instruction CLRWDT) every time it nears its overflow. Thus program will
prevent a reset as long as it's executing correctly. Once it gets stuck, zero will be written, overflow
of WDT timer and a reset will occur which will bring the microcontroller back to correct functioning
again.

Prescaler is accorded to timer TMRO, or to watchdog timer with the help of PSA bit in OPTION
register. By clearing PSA bit, prescaler will be accorded to timer TMRO. When prescaler is accorded
to timer TMRO, all instructions of writing to TMRO register (CLRF TMRO, MOVWF TMRO, BSF
TMRO,...) will clear prescaler. When prescaler is assigned to a watchdog timer, only CLRWDT
instruction will clear a prescaler at the same time watchdog clears it. Prescaler change is
completely under programmer's control, and can be changed while program is running.

There is only one prescaler and one timer. Depending on the needs, they are accorded
either to timer TMRO or to a watchdog.

OPTION Control Register

R/'/V-1

RW-1

R/W-1

R/'/V-1

R/W-1

RBPU * 1J "

INTEDG

TOCS

TOSE

PSA

PS2

PS1

PSO

bit 7

bit

Legend:

R = Readable bit W = Writable bit

U = Unimplemented bit, read as '0' -n = Value at POR reset

Bit 0:2 PSO, PS1, PS2 (Prescaler Rate Select bit)

The subject of a prescaler, and how these bits affect the work of a microcontroller will be covered

in section on TMRO.

Bits

TRM0

WDT

000

ooi

010

Oil

100

101

110

12S

256

128

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Chapter 2 - Microcontroller PIC16F84

bit 3 PSA (Prescaler Assignment bit)

Bit which assigns prescaler between TMRO and watchdog timer.

l=prescaler is assigned to watchdog timer.

0=prescaler is assigned to free timer TMRO

bit 4 TOSE (TMRO Source Edge Select bit)

If we are able to trigger TMRO with impulses from a RA4/T0CKI pin, this bit will determine whether
it will be on the rising or falling edge of a signal.
l=falling edge
0=rising edge

bit 5 TOCS (TMRO Clock Source Select bit)

This pin enables a free timer to increment its status either from an internal oscillator, which is on

every 1 of oscillator clock, or via external impulses on RA4/T0CKI pin.

l=external impulses

0=1/4 internal clock

bit 6 INTEDG (Interrupt Edge Select bit)

If occurrence of interrupts is enabled, this bit will determine at what edge interrupt on RBO/INT

pin will occur.

1= "pull-up" resistors turned off

0= "pull-up" resistors turned on

bit 7 RBPU (PORTB Pull-up Enable bit)

This bit turns internal pull-up resistors on port B on or off.

l= , pull-up' resistors turned on

0= , pull-up' resistors turned off

a Previous Table of Chapter Npy1 - n3np k

™ page contents overview |>1CAL M^y c w

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Chapter 2 - Microcontroller PIC16F84

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2.8 EEPROM Data memory

PIC16F84 has 64 bytes of EEPROM memory locations on addresses from OOh to 63h that can be
written to or read from. The most important characteristic of this memory is that it does not loose
its contents during supply. That practically means that what is written to it remains even if
microcontroller is turned off. Data can be retained in EEPROM without supply for up to 40 years
(as maker of PIC16F84 microcontroller says), and up to 10000 cycles of writing can be executed.

In practice, EEPROM memory is used for storing important data or some process parameters.
One such parameter is a given temperature, assigned when setting up a temperature regulator to
some process. In case that this data isn't retained, it will be necessary to adjust a given
temperature after each loss of supply. Since this is very impractical (and even dangerous), makers
of microcontrollers have began installing one smaller type of EEPROM memory.

EEPROM memory is contained in a special memory space and can be accessed through special
registers. These registers are:

• EEDATA at address 08h, which holds data that is read or that needs to be written.

• EEADR at address 09h, which contains an address of EEPROM location being accessed.

• EECON1 at address 88h, which contains control bits.

• EECON2 at address 89h. This register does not exist physically and serves to protect EEPROM
from accidental writing.

EECON1 register at address 88h is a control register with five applied bits.

Bits 5, 6 and 7 are not used, and when read always are zero. Interpretation of EECON1 register

bits follows.

EECONl Register

U-0

R/W-1

R/'/V-x

R/S-0

R/S-x

EEIF <D

WRERR

i/VREN

bit 7

bit

Legend:

R= Readable bit W= Writable bit

U = Unimplemented bit, read as '0' -n = Value at POR reset

bit RD (Read Control bit)

Setting this bit initializes transfer of data from address defined in EEADR to EEDATA register. Since
time is not as essential in reading data as in writing, data from EEDATA can already be used
further in the next instruction.

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Chapter 2 - Microcontroller PIC16F84

l=initializes reading
0=does not initialize reading

bit 1 WR (Write Control bit)

Setting of this bit initializes writing data from EEDATA register to the address on EEADR register.

l=initializes writing

0=does not initialize writing

bit 2 WREN (EEPROM Write Enable bit) Enables writing to EEPROM
If this bit is not set, microcontroller will not allow writing to EEPROM.
l=writing allowed
0=writing disallowed

bit 3 WRERR (EEPROM Error Flag bit) Error during writing to EEPROM

This bit is set only in cases when writing to EEPROM was interrupted by a reset signal or by

running out of time in watchdog timer (if it's activated).

l=error occured

0=error did not occur

bit 4 EEIF (EEPROM Write Operation Interrupt Flag bit) Bit used to inform that writing data to

EEPROM has ended.

When writing has terminated, this bit will be set automatically. Programmer must reset EEIF bit in

his program in order to detect new termination of writing.

l=writing terminated

0=writing not terminated yet, or has not started

Reading from EEPROM Memory

Setting the RD bit initializes transfer of data from address found in EEADR register to EEDATA
register. As in reading data we don't need so much time as in writing, data taken over from
EEDATA register can already be used further in the next instruction.

Sample of the part of a program which reads data in EEPROM, could look something like the
following:

bcf STATUS, RPU
movlu 0x00
movuf EEADR

bsf STATUS, RPO

bsf EECON1, RD

bcf STATUS, RPO

movf EEDATA, W

;bankO, because EEADR is at 09h
; address of location being read
; address transferred to EEADR
;bankl because EECON1 is at S8h
; reading from EEPROM
;BankO because EEDATA is at OSh
;U < — EEDATA

After the last program instruction, contents from an EEPROM address zero can be found in working
register w.

Writing to EEPROM Memory

In order to write data to EEPROM location, programmer must first write address to EEADR register
and data to EEDATA register. Only then is it useful to set WR bit which sets the whole action in

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Chapter 2 - Microcontroller PIC16F84

motion. WR bit will be reset, and EEIF bit set following a writing which may be used in processing
interrupts. Values 55h and AAh are the first and the second key which make it impossible for
accidental writing to EEPROM to occur. These two values are written to EECON2 which serves only
that purpose, to receive these two values and thus prevent any accidental writing to EEPROM
memory. Program lines marked as 1, 2, 3, and 4 must be executed in that order in even time
intervals. Therefore, it is very important to turn off interrupts which could change the timing
needed for executing instructions. After writing, interrupts can be enabled again in the end.

Example of the part of a program which writes data OxEE to first location in EEPROM memory
could look something like the following:

1)
2)
3)
4)

bcf STATUS, RPO
rtiovlw OxOO

rciovuf EEADR

movlu OxEE
movuf EEDATA
bsf STATUS, RPO
bcf INTCON, GIE
bsf EECON1, UREN
movlu 5Sh
movuf EECON2
movlu AAh
movuf EECON2
bsf EEC0N1,UR

bsf INTCON, GIE

;bankO, because EEADR is at 09h

; address of location being

; written to

; address being transferred to

; EEADR

; write the value OxEE

;data goes to EEDATA register

;Bankl because EEADR is at 09h

;all interrupts are disabled

; writing enabled

; first key 55h — > EECON2

; second key AAh — > EECON2
; initialises writing

; interrupts are enabled

It is recommended that WREN be turned off the whole time except when writing data to

EEPROM, so that possibility of accidental writing would be minimal.

All writing to EEPROM will automatically clear a location prior to writing anew!

reviews

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Chapter 3 - Instruction Set

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CHAPTER 3

I nstruction Set

Introduction

Instruction set in PIC16Cxx microcontroller family

Data Transfer

Arithmetic and logic

Bit operations

Directing the program flow

Instruction execution period

Word list

I ntroduction

We have already mentioned that microcontroller is not like any other integrated circuit. When they
come out of production most integrated circuits are ready to be built into devices which is not the
case with microcontrollers. In order to "make" microcontroller perform a task, we have to tell it
exactly what to do, or in other words we must write the program microcontroller will execute. We
will describe in this chapter instructions which make up the assembler, or program language for
PIC microcontrollers of lower standard.

Instruction Set in PIC16Cxx Microcontroller Family

Complete set which encompasses 35 instructions is given in the following table. A reason for such
a small number of instructions lies primarily in the fact that we are talking about a RISC
microcontroller whose instructions are well optimized considering the speed of work, architectural
simplicity and code compactness. The only drawback is that programmer is expected to master
"uncomfortable" technique of using a modest set of 35 instructions.

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Chapter 3 - Instruction Set

Data transfer

Transfer of data in a microcontroller is done between work (W) register and an 'f register that
represents any location in internal RAM (regardless whether those are special or general purpose
registers).

First three instructions (look at the following table) provide for a constant being written in W
register (MOVLW is short for MOVe Literal to W), and for data to be copied from W register onto
RAM and data from RAM to be copied onto W register (or on the same RAM location, at which
point only the status of Z flag changes). Instruction CLRF writes constant in 'f ' register, and
CLRW writes constant in register W. SWAPF instruction exchanges places of the 4- bit nibbles
crosswise inside a register.

Arithmetic and logic

Of all arithmetic operations, PIC like most microcontrollers supports only subtraction and addition.
Flags C, DC and Z are set depending on a result of addition or subtraction, but with one exception
since subtraction is performed like addition of a negative value, C flag is inverse following a
subtraction. In other words, it is set if operation is possible, and reset if larger number was
subtracted from a smaller one.

Logic one of PIC has capability of performing operations AND, OR, EX-OR, negations (COMF) and
rotation (RLF and RRF).

Instructions which rotate the register contents move bits inside a register through flag C by one
space to the left (toward bit 7), or to the right (toward bit 0). Bit which "comes out" of a register
is written in flag C, and status of that flag is written in a bit on the "opposite side" of the register.

Bit operations

Instructions BCF and BSF do setting or resetting of one bit anywhere in the memory. Even though
this seems like a simple operation, it is executed so that CPU first reads the whole byte, changes
one bit in it and then writes in the entire byte at the same place.

Directing a program flow

Instructions GOTO, CALL and RETURN are executed the same way as on all other microcontrollers,
only stack is independent of internal RAM and limited to eight levels.

'RETLW k' instruction is identical with RETURN instruction, except that before coming back from a
subprogram a constant defined by instruction operand is written in W register. This instruction
enables us to design easily the Lookup tables (lists). Mostly we use them by determining data
position on our table adding it to the address at which the table begins, and then we read data
from that location (which is usually found in program memory).

Table can be formed as a subprogram which consists of a series of 'RETLW k' instructions, where
'k' constants are members of the table.

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Chapter 3 - Instruction Set

Main molov 2

call Lookup

Lookup addwf PCL, f
retlw k
retlw kl
retlw k2

retlw kn

We write the position of a member of our table in W register, and using CALL instruction we call a
subprogram which makes up the table. First subprogram line ADDWF PCL, f adds the position of a
W register member to the starting address of our table, found in PCL register, and so we get the
real data address in program memory. When returning from a subprogram we will have in W
register the contents of an addressed table member. In a previous example, constant 'k2' will be
in W register following a return from a subprogram.

RETFIE (RETurn From Interrupt - Interrupt Enable) is a return from interrupt routine and differs
from a RETURN only in that it automatically sets GIE (Global Interrupt Enable) bit. Upon an
interrupt, this bit is automatically reset. As interrupt begins, only the value of program counter is
put at the top of a stack. No automatic storing of register status is provided.

Conditional jumps are synthesized into two instructions: BTFSC and BTFSS. Depending on a bit
status in 'f register that is being tested, instructions skip or don't skip over the next program
instruction.

I nstruction Execution Period

All instructions are executed in one cycle except for conditional branch instructions if condition is
true, or if the contents of program counter is changed by some instruction. In that case, execution
requires two instruction cycles, and the second cycle is executed as NOP (No Operation). Four
oscillator clocks make up one instruction cycle. If we are using an oscillator with 4MHz frequency,
the normal time for executing an instruction is 1 \is, and in case of conditional branching,
execution period is 2 |js.

Word list

f any memory location in a microcontroller

W work register

b bit position in 'f register

d destination bit

label group of eight characters which marks the beginning of a part of the program

TOS top of stack

[] option

<> register bit field

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Chapter 3 - Instruction Set

Mnemonic

Description

Fleg

CLK

Notes

Data transfer

MOVLW

Move literal to W

k-» W

MOVWF

Move W to f

W-»f

MOVF

f, d

Move f

f-* d

1,2

CLRW

Clear W

0-* W

CLRF

Clear f

0-*f

SWAPF

fid

Swap nibbles in f

f(7:4),(3:0)-rf(3:0M7:4)

1.2

Arithmetic and logic

ADDLW

Add literal and W

W+1-* W

DC,

ADDWF

fid

Add W andf

W+f-» d

DC,

1,2

SUBLW

Subtract W from liter a

W-k -* d

DC,

SUBWF

f, d

Subtract W from f

W-f-^d

DC,

1,2

ANDLW

AND literal with W

W .AND, k-»W

ANDWF

f. d

AND W with f

W .AND. f-* d

1, 2

IORLW

Inclusive OR literal with W

W .OR. k-=> W

IORWF

fid

Inclusive OR W with f

W .OR.f-» d

1,2

XORWF

f. d

Exclusive OR W with f

W .XOR. k-*W

1. 2

..V.OQ! W

..'.' ■

.-^'^.". >::■■.? rt n litonl 'h^.* •

.^-W vnR f ) d _.. ..

■ ■ M

J7.

1 H

1 -— "■

iriJl^ii^it f ' i

I : j ■-.* f l t f

y -- £■. r I'-- -4 a'^' f

• ljl . 1

L j'^ir jiil i

t : n ■' " " i

? ' '

r i ■

*■- 1

i j--:-* ■ "~

'", •] ■

korare Left f through Cirr/

-:c;-< "■ii'fi'i r:ir|

1,2 "

RL U "

f. d

R otate R i qht f th ro u q h Carry

■ k 7 a; s \* j"3 [2"j i ; q>— >fcfr

1. 2

RRF

fid

Complement f

f-»d

1,2

COMF

Bit operations

f. b

Bit clear f

-> f (bl

1. 2

BCF

fib

Bit Set f

l-»f(b)

1,2

BSF

Directing a program flow

f,b

Bit Test fj Skip if Clear

jump iff(b)=0

1(2)

BTFSC

f,b

Bit Test f j Skip if Set

jump if f(b)=l

1(2)

BTFSS

f, d

Decrement f j Skip if

f+ 1 -*■ dj j urn p if = 1

1(2)

1,2,3

DECFSZ

f,d

I n ere m e n t f j Skip if

f-1 -*■ 6, jump if = 1

1(2)

1,2,3

INCFSZ

Go to address

k-» PC

GOTO

Call subroutine

PC-»TOS, k-» PC

CALL

Return from Subroutine

TOS-* PC

RETURN

Return with literal in W

k -» W, TOS -» PC

RETLW

Return from interrupt

TOS-* PC, 1 -* GIE

RETFIE

Other instructions

No Operation

NOP

C 1 ea r W a tch d o q Ti m e r

0-» WDT, 1 -*TO, 1 -»PD

TO, PD

CLRWDT

Go into stan by mode

0-» WDT, 1 -»TO, 0-»PD

TO, PD

SLEEP

* 1 If I/O port is source operand, status on microcontroller pins is read

*2 If this instruction is executed on TMR register and if d = l, prescaler assigned to that timer will

automatically be cleared

*3 If PC is modified, or test result =1, instruction is executed in two cycles.

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Chaptec 9 78Bssembly Language Programming

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CHAPTER 4

Bssembly Language Programming

Introduction

Bn example of a written program

Control directives

4.1 define

4.2 include

4.3 constant

4.4 variable

4.5 set

4.6 equ

4.7 org

4.8 end

Conditional instructions

4.9 if

4.10 else

4.11 endif

4.12 while

4.13 endw

4.14 ifdef

4.15 ifndef

Data directives

4.16 cblock

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Chapter 4 - Assembly Language Programming

q 4.17 endc

q 4.18 db

q 4.19 de

q 4.20 dt

Configurating a directive

q 4.21 CONFIG
q 4.22 Processor

Assembler arithmetic operators

Files created as a result of program translation

Macros

I ntroduction

The ability to communicate is of great importance in any field. However, it is only possible if both
communication partners know the same language, or follow the same rules during communication
Using these principles as a starting point, we can also define communication that occurs between
microcontrollers and man . Language that microcontroller and man use to communicate is called
"assembly language". The title itself has no deeper meaning, and is analogue to names of other
languages , ex. English or French. More precisely, "assembly language" is just a passing solution.
Programs written in assembly language must be translated into a "language of zeros and ones" in
order for a microcontroller to understand it. "Assembly language" and "assembler" are two
different notions. The first represents a set of rules used in writing a program for a
microcontroller, and the other is a program on the personal computer which translates assembly
language into a language of zeros and ones. A program that is translated into "zeros" and "ones"
is also called "machine language".

Program, asm

Translator

Program. hew

Programmer

[

Han

RA2

RA1

RA3

RAO

RA4T

XKI

PIC

0SC1
0SC2

MCLR

Vss

16F84

Vdd

RB0AWT

RB7

RBI

RB6

RB2

RB5

RB3

RB4

]

12-

]

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Chapter 4 - Assembly Language Programming

The process of communication between a man and a microcontoller

Physically, "Program" represents a file on the computer disc (or in the memory if it is read in a
microcontroller), and is written according to the rules of assembly or some other language for
microcontroller programming. Man can understand assembly language as it consists of alphabet
signs and words. When writing a program, certain rules must be followed in order to reach a
desired effect. A Translator interprets each instruction written in assembly language as a series
of zeros and ones which have a meaning for the internal logic of the microcontroller.
Lets take for instance the instruction "RETURN" that a microcontroller uses to return from a sub-
program.

When the assembler translates it, we get a 14- bit series of zeros and ones which the
microcontroller knows how to interpret.

Example: RETURN 00 0000 0000 1000

Similar to the above instance, each assembly instruction is interpreted as corresponding to a
series of zeros and ones.

The place where this translation of assembly language is found, is called an "execution" file. We
will often meet the name "HEX" file. This name comes from a hexadecimal representation of that
file, as well as from the appendage "hex" in the title, ex. "run through. hex". Once it is generated,
the execution file is read in a microcontroller through a programmer.

An Assembly Language program is written in a program for text processing (editor) and is
capable of producing an ASCII file on the computer disc or in specialized surroundings such as
MPLAB - to be explained in the next chapter.

Assembly language

Basic elements of assembly language are

Labels

Instructions

Operands

Directives

Comments

Labels

A Label is a textual designation (generally an easy-to-read word) for a line in a program, or
section of a program where the micro can jump to - or even the beginning of set of lines of a

program. It can also be used to execute program branching (such as Goto ) and the program

can even have a condition that must be met for the Goto instruction to be executed. It is
important for a label to start with a letter of the alphabet or with an underline "_". The length of
the label can be up to 32 characters. It is also important that a label starts in the first row.

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Chapter 4 - Assembly Language Programming

first column —

Correctly written labels

Start
_end
P123
Is_it_bigger?

Incorrectly written labels

Sta rt ~ c ' oes n °t begin in first column
2 end - begins with a number!

Instructions

Instructions are already defined by the use of a specific microcontroller, so it only remains for us
to follow the instructions for their use in assembly language. The way we write an instruction is
also called instruction "syntax". In the following example, we can recognize a mistake in writing
because instructions movlp and gotto do not exist for the PIC16F84 microcontroller.

Correctly written instructions

movlw
goto

H'OIFF 1
Start

Incorrectly written instructions

movlp
gotto

H'OIFF'

Start

Operands

Operands are the instruction elements for the instruction is being executed. They are usually
registers or variables or constants. Constants are called "literals." The word literal means
"number."

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Chapter 4 - Assembly Language Programming

Typical Operands:

movlw H'OFF 1
movwf NIVO

Operand as a

variable NIVO in the

memory of a

microcontroller

Operand as a
hexadecimal number

Comments

Comment is a series of words that a programmer writes to make the program more clear and
legible. It is placed after an instruction, and must start with a semicolon

ii . M

Directives

A directive is similar to an instruction, but unlike an instruction it is independent on the
microcontroller model, and represents a characteristic of the assembly language itself. Directives
are usually given purposeful meanings via variables or registers. For example, LEVEL can be a
designation for a variable in RAM memory at address ODh. In this way, the variable at that
address can be accessed via LEVEL designation. This is far easier for a programmer to understand
than for him to try to remember address ODh contains information about LEVEL.

Some frequently used directives:

PROCESSOR 16F84
include "p1GfB4.inc"

CONFIG CP OFF& WDT OFF & PWRTE ON & XT OSC

An example of a written program

The following example illustrates a simple program written in assembly language respecting the
basic rules.

When writing a program, beside mandatory rules, there are also some rules that are not written
down but need to be followed. One of them is to write the name of the program at the beginning,
what the program does, its version, date when it was written, type of microcontroller it was
written for, and the programmer's name.

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Chapter 4 - Assembly Language Programming

Basic

information

on the

program

Directive

Inclusion of
a macro

Comment

Label
Instruction

Operand

; Program for initialization of port B and setting pins to status of logic one
; Version 1.0 Date: 10.10.1999. MCU:PIC16F84 Written by: John Smith

; Declaration and configuration of a processor
PROCESSOR 16F84
^include "piefS^inc" ; Processor title

CONFIG CP OFF& WDT OFF & PWRTE ON & XT OSC

org
goto

0x00
Main

org 0x04
goto Main
^include "bank.inc 1

Main

BANK1

movlw 0x00
movwf TRISB
BANK0

movlw OxFF

movwf PORTB
Loop goto Loop
end

; Start of program

; Reset vector

j Go to the beginning of Main sub-routine

; Interrupt vector

; Interrupt routine doesn't exist

; Beginning of the main program
; Select memory bank 1

j Port B pins are output
; Select memory bank

; Set all ones to port B

; Program remains in the loop

; Necessary marking the end of a program

Since this data isn't important for the assembly translator, it is written as comments. It should be
noted that a comment always begins with a semicolon and it can be placed in a new row or it can
follow an instruction. It's best kept in the third row to make the layout easy to follow.
After the opening comment has been written, the directive must be included. This is shown in the
example above.

In order to function properly, we must define several microcontroller parameters such as: - type
of oscillator,

- whether watchdog timer is turned on, and

- whether internal reset circuit is enabled.
All this is defined by the following directive:

_CONFIG _CP_OFF&_WDT_OFF&PWRTE_ON&XT_OSC

When all the needed elements have been defined, we can start writing a program.

First, it is necessary to determine an address from which the microcontroller starts, following a

power supply start-up. This is (org 0x00).

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Chapter 4 - Assembly Language Programming

The address from which the program starts if an interrupt occurs is (org 0x04).

Since this is a simple program, it will be enough to direct the microcontroller to the beginning of a

program with a "goto Main" instruction.

The instructions found in the Main sub-routine select memory bankl (BANK1) in order to access
TRISB register, so that port B can be declared as an output (movlw 0x00, movwf TRISB).

The next step is to select memory bank and place status of logic one on port B (movlw OxFF,
movwf PORTB), and thus the main program is finished.

We need to make another loop where the micro will be held so it doesn't "wander" if an error
occurs. For that purpose, one infinite loop is made where the micro is retained while power is
connected. The necessary "end" at the conclusion of each program informs the assembly
translator that no more instructions are in the program.

Control directives

4.1 #DEFINE Exchanges one piece of text for another

Syntax:

#define<name> [<text which changes name>]

Description:

Each time <name> appears in the program , it will be exchanged for <text which changes name>

Example:

tfdefine turned on 1
if define turned off

Similar directives: #UNDEFINE, IFDEFJFNDEF

4.2 INCLUDE Include an additional file in a program

Syntax:

#include <file_name>
#include "

Description:

An application of this directive has the effect as though the entire file was copied to a place where
the "include" directive was found. If the file name is in the square brackets, we are dealing with a
system file, and if it is inside quotation marks, we are dealing with a user file. The directive
"include" contributes to a better layout of the main program.

Example:

^include <regs.h>

# include "subprog. asm"

4.3 CONSTANT Gives a constant numeric value to the textual

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Chapter 4 - Assembly Language Programming

designation

Syntax:

Constant <name>=<value>

Description:

Each time that <name> appears in program, it will be replaced with <value>.

Example:

Constant MAXIMUM=100
Constant Length=30

Similar directives: SET, VARIABLE

4.4 VARIABLE Gives a variable numeric value to textual
designation

Syntax:

Variable<name>=<value>

Description:

By using this directive, textual designation changes with particular value.

It differs from CONSTANT directive in that after applying the directive, the value of textual

designation can be changed.

Example:

variable level=20
variable time=13

Similar directives: SET, CONSTANT

4.5 SET Defining assembler variable

Syntax:

<name_variable>set<value>

Description:

To the variable <name_variable> is added expression <value>. SET directive is similar to EQU,
but with SET directive name of the variable can be redefined following a definition.

Example:

level set

length set 12
level set 45

Similar directives: EQU, VARIABLE

4.6 EQU Defining assembler constant

Syntax:

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Chapter 4 - Assembly Language Programming

<name_constant> equ <value>

Description:

To the name of a constant <name_constant> is added value <value>

Example:

five equ 5
six equ 6
seven equ 7

Similar instructions: SET

4.7 ORG Defines an address from which the program is stored in
microcontroller memory

Syntax:

Description:

This is the most frequently used directive. With the help of this directive we define where some
part of a program will be in the program memory.

Example:

Start org 0x00
movlw
movwf

The first two instructions following the first 'org' directive are stored from address 00, and the
other two from address 10.

4.8 END End of program

Syntax:

end

Description:

At the end of each program it is necessary to place 'end' directive so that assembly translator
would know that there are no more instructions in the program.

Example:

movlw OxFF
movwf PORTB
end

Conditional instructions

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Chapter 4 - Assembly Language Programming

4.9 IF Conditional program branching

Syntax:

if<conditional_term>

Description:

If condition in <conditional_term> is met, part of the program which follows IF directive will be
executed. And if it isn't, then the part following ELSE or ENDIF directive will be executed.

Example:

if nivo=100

goto PUNI

else

goto PRAZNI

endif

Similar directives: #ELSE, ENDIF

4.10 ELSE 'IF 1 alternative to program block with conditional terms

Syntax:

Else

Description:

Used with IF directive as an alternative if conditional term is incorrect.

Example:

If time< 50

goto SPEED UP

else goto SLOW DOWN

endif

Similar instructions: ENDIF, IF

4.11 ENDIF End of conditional program section

Syntax:

endif

Description:

Directive is written at the end of a conditional block in order for the assembly translator to know
that it is the end of the conditional block

Example:

If level=100

goto LOADS

else

goto UNLOADS

endif

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Chapter 4 - Assembly Language Programming

Similar directives: ELSE, IF

4.12 WHILE Execution of program section as long as condition is
met

Syntax:

while<condition>

endw

Description:

Program lines between WHILE and ENDW will be executed as long as condition is met. If a
condition stops being valid, program continues executing instructions following ENDW line.
Number of instructions between WHILE and ENDW can be 100 at the most, and number of
executions 256.

Example:

While 1<10

±=i+l

endw

4.13 ENDW End of conditional part of the program

Syntax:

endw

Description:

Instruction is written at the end of the conditional WHILE block, so that assembly translator would
know that it is the end of the conditional block

Example:

while i<10
1=1+1

endw

Similar directives: WHILE

4.14 IFDEF Execution of a part of the program if symbol is
defined

Syntax:

ifdef<designation>

Description:

If designation <designation> is previously defined (most commonly by #DEFINE instruction),
instructions which follow are executed until ELSE or ENDIF directives are not reached.

Example:

tfdefine test

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Chapter 4 - Assembly Language Programming

ifdef test ;how the test is defined

; instructions from these lines will execute

endif

Similar directives: #DEFINE, ELSE, ENDIF, IFNDEF, #UNDEFINE

4.15 IFNDEF Execution of a part of the program if symbol is
defined

Syntax:

ifndef<designation>

Description:

If designation <designation> was not previously defined, or if its definition was erased with
directive #UNDEFINE, instructions which follow are executed until ELSE or ENDIF directives are
not reached.

Example:

ftdefine test

ftundefine test

ifndef test ;how the test is undefined

; instructions from these lines will execute

endif

Similar directives: #DEFINE, ELSE, ENDIF, IFDEF, #UNDEFINE

Data Directives

4.16 CBLOCK Defining a block for the named constants

Syntax:

Cblock [<term>]

<label>[: <increment>], <label>[: <increment>]

endc

Description:

Directive is used to give values to named constants. Each following term receives a value greater
by one than its precursor. If <increment> parameter is also given, then value given in
<increment> parameter is added to the following constant.
Value of <term> parameter is the starting value. If it is not given, it is considered to be zero.

Example:

Cblock 0x02

First, second, third ; first=0x02 f second=0x03 f third=0x04

endc

cblock 0x02

first : 4, second : 2, third ; first=0x06, second=0x08 f third=0x09

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Chapter 4 - Assembly Language Programming

endc

Similar directives: ENDC

4.17 ENDC End of constant block definition

Syntax:

endc

Description:

Directive is used at the end of a definition of a block of constants so assembly translator could
know that there are no more constants.

Similar directives: CBLOCK

4.18 DB Defining one byte data

Syntax:

[<term>]db <term> [, <term>, ,<term>]

Description:

Directive reserves a byte in program memory. When there are more terms which need to be
assigned a byte each, they will be assigned one after another.

Example:

db 't', OxOf, 'e', 's', 0x12

Similar instructions: DE, DT

4.19 DE Defining the EEPROM memory byte

Syntax:

[<term>] de <term> [, <term>, , <term>]

Description:

Directive is used for defining EEPROM memory byte. Even though it was first intended only for
EEPROM memory, it can be used for any other location in any memory.

Example:

org H'2100 '

de "Version 1.0" ,

Similar instructions: DB, DT

4.20 DT Defining the data table

Syntax:

[<term>] dt <term> [, <term>, , <term>]

Description:

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Chapter 4 - Assembly Language Programming

Directive generates RETLW series of instructions, one instruction per each term
Example:

dt "Message",

dt first, second, third

Similar directives: DB, DE

Configurating a directive

4.21 _CONFIG Setting the configurational bits

Syntax:

■ -config<term> or config<address>,<term>

Description:

Oscillator, watchdog timer application and internal reset circuit are defined. Before using this
directive, the processor must be defined using PROCESSOR directive.

Example:

_CONFIG _CP_OFF&_WDT_OFF&_PWRTE_ON&_XT_OSC

Similar directives: JDLOCS, PROCESSOR

4.22 PROCESSOR Defining microcontroller model

Syntax:

Processor <microcontroller_type>

Description:

Instruction sets the type of microcontroller where programming is done.

Example:

processor 16F84

Assembler arithmetic operators

Operator Description Example

$ Current status of program counter goto J +3

( Left bracket 1 + ( d * 4 )

) Right bracket ( Length + 1 ) * 256

! NE (logic complement) if ! ( a - b )

Complement flags = -flags

Negation (second complement) -1 * Length

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high
low

<<
>>
> =

>
<
< =

Chapter 4 - Assembly Language Programming

Negation (second complement)

Returns higher byte

Returns lower byte

Multiplying

Subdividing

Subdividing by module

Addition

Subtraction

Moving to the left

Moving to the right

Higher than, or equal

Higher than

Lesser than

Lesser than, or equal

Equal

Not equal

Operation AND on bits

Exclusive OR on bits

Logic OR on bits
Logic AND

Logic OR

Equal

Add and assign

Subtract and assign

Multiply and assign

Divide and assign

Divide at module and assign

Move to the left and assign

Move to the right and assign

Logic AND and assign

Logic OR on bits and assign

Exclusive OR on bits and assig

Increment by one

Decrease by one

i
ii

+ =

/ =
9 o =
«=
»=

A—

-1 * Length

movlw high CTR_Table

movlw low CTR_Table

a = b * c

a = b / c

entry_len = tot J en % 16

tot J en = en try J en * 8 + 1

entryjen = ( tot - 1 ) / 8

va\ = flags << 1

val = flags >> 1

f entry_
f entry_
f entry_
f entry_
f entry_
f entry_

dx >= num_entries

dx > num_entries

dx < num_entries

dx <= num_entries

dx == num_entries

dx != num_entries

flags = flags & ERROR_BIT

flags = flags ^ ERROR_BIT

flags = flags | ERROR_BIT
if (len == 512) && (b == c)

if (len == 512) || (b == c)
entry_index =
entry_index +=1
entry_index -= 1
entry_index * = entryjength
entry_total /= entryjength
entry_index %= 8
flags «=3
flags »=3

flags &=ERROR_FLAG
flags |=ERROR_ELAG
flags^=ERROR_FLAG
i++

i ~

Files created as a result of program translation

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Chapter 4 - Assembly Language Programming

As a result of the process of translating a program written in assembler language we get files like:

q Executing file (Program_Name.HEX)

q Program errors file (Program_Name.ERR)

q List file (Program_Name.LST)

The first file contains translated program which is read in microcontroller by programming. Its
contents can not give any information to programmer, so it will not be considered any further.
The second file contains possible errors that were made in the process of writing, and which were
noticed by assembly translator during translation process. Errors can be discovered in a "list" file
as well. This file is more suitable though when program is big and viewing the list' file takes
longer.

The third file is the most useful to programmer. Much information is contained in it, like
information about positioning instructions and variables in memory, or error signalization.

Example of 'list' file for the program in this chapter follows. At the top of each page is found
information about the file name, date when it was translated, and page number. First column
contains an address in program memory where a instruction from that row is placed. Second
column contains a value of any variable defined by one of the directives : SET, EQU, VARIABLE,
CONSTANT or CBLOCK. Third column is reserved for the form of a translated instruction which PIC
is executing. The fourth column contains assembler instructions and programmer's comments.
Possible errors will appear between rows following a line in which the error occured.

HP ASH 02 . 40 Hel e ase d

LOC OBJECT CODE
VALUE

00001
00002
00003
00004
00005
00006
00007
00008
00001
00002

00136
00009
00010
00011
00012
00013
00014
00015
00016
00017
0001S
00019

2007 3FF1
00 OC

0000
0000 2805

0004

-1-11- H

Hakro: Proba.lst

PROEA.ASH

LINE SOURCE TEXT

4-26-2000 7:13:17

PACE

; Pro gram for initialization of port E and setting its pins
;to the state of logic one

;Version: 1.0 Date: 10.05-2000. HCU: PIC16F84 Written

;by: Petar Petrovic

declaration and configuration of the processor

PROCESSOR 16F84

^include "pl6f84.inc" ;Processor title

LIST

;P16F84.IHC Standard Header File, Version 2.00

; Technology, Inc.

LIST

Hicrochip

CONFIG

CP OFF 4 TiTDT OFF 4 PURTE ON 4 XT OSC

CONSTANT EASE = 0x0c

; Start of a program

org 0x00 ; Reset vector

goto Main ;Go to the beginning of the main program

; Int e r rupt ve ct or

org 0x04 ; Interrupt vector

■-■ on r

TWj-.^

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Chapter 4 - Assembly Language Programming

*J U ■_■_!_ u

r j_xj^_- c j- j.

■-■L^.' ^ V — ■_ ■_■■_■ J_

0004

00019

org

0x04 ;Int«

5rn.pt vector

0004 2S0S

00020
00021

goto

Main ;Inti

arrupt routine does not exist

00022

; Be ginning of the main program

00023

^include "Bank . inc "

; File with macros

00001

00002

Makros BAHKC

and BAHK1

00003

00004

0000 0010

OOOOS

W_Temp

set

BASE+4

0000 0011

00006

Stat_Temp set

EASE+S

0000 0012

00007
00008
00009

Option

T eiup s et

BASE+6

00010

BAHE0

macro

00011

bcf

STATUS,RP0

; Select memory bank

00012

endm

00013

00014

BAHK1

macro

0001S

bsf

STATUS,RP0

; Select memory bank 1

00016

endm

00017

0005

00024

Ma iji

0002S

BAHK1

; Select memory batik 1

00 OS 1683

bsf

STATUS,RP0

; Select memory batik 1

0006 3000

00026

movlu

0x00

Message [302] :

rand not in batik 0. Ensure that bank bits are

correct.

0007 0086

00027
00028

mcnrwf

TRISB

;Port B pins are output

00029

BAHK0

;Select memory bank

0008 1283

bcf

STATUS, RP0

;Select memory bank

0003 30FF

00030

movlw

OxFF

000A 0086

00031
00032

movxrf

P0RTB

;Set all ones to port B

OOOB 280E

00033
00034

Loop

goto Loop

; Program stays in the loop

0003S

EHD

;Heci

sssary marking the end of a program

MEMORY USAGE

MAP ( ' X

1 = Used,

1 - ' = Unus

ed)

0000 : X XX>XXXXX--

■?nnn

- V

lIUUU

All other memory blocks unuse

Program Memory Words

Used:

Program Memory Words

Free:

1015

Errors:

Warnings :

reported.

suppress

Me ss age s :

1 reported,

suppress

At the end of the "list" file there is a table of symbols used in a program. Useful element of 'list'

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Chapter 4 - Assembly Language Programming

file is a graph of memory utilization. At the very end, there is an error statistic as well as the

amount of remaining program memory.

Macros

Macros are a very useful element in assembly language. They could briefly be described as "user
defined group of instructions which will enter assembler program where macro was called". It is
possible to write a program even without using macros. But with their use written program is
much more legible, especially if more programmers are working on the same program. Macros
have the same purpose as functions of complex program languages.

How to write them:

<label> macro [<argumentl>,<argument2>, <argumentN>]

endm

From the way they are written, we see that macros can accept arguments, which is also very
useful in programming. Whenever argument appears in the body of a macro, it will be replaced
with the <argumentN> value.

Example:

NA_PORTB macro ARG1

BANKO ;Select memory bank

movlw ARG1 ;Value from ARG1 argument

;is stored in working register
movwf PORTB ;value from ARG1

; argument placed on port B
endm ;macro ended

The above example shows a macro whose purpose is to place on port B the ARG1 argument that
was defined while macro was called. Its use in the program would be limited to writing one line:
ON_PORTB OxFF , and thus we would place value OxFF on PORTB. In order to use a macro in the
program, it is necessary to include macro file in the main program with instruction include
"macro_name.inc". Contents of a macro is automatically copied onto a place where this instruction
is written. This can be best seen in a previous list file where file with macros is copied below the
line #include"bank.inc"

a Previous Table of Chapter Npy1 - n - np k

^ page contents overview |>1CAL i ja y c r

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Chapter 5 - MPLAB

Table of
contents

Chapter
overview

Next page ►

CHAPTER 5

MPLAB

Introduction

5.1 Installing the MPLAB program package

5.2 Introduction to MPLAB

5.3 Choosing the development mode

5.4 Designing a project

5.5 Designing new assembler file

5.6 Writing a program

5.7 MPSIM simulator

5.8 Toolbar

I ntroduction

MPLAB is a Windows program package that makes writing and developing a program easier. It
could best be described as developing environment for some standard program language that is
intended for programming a PC computer. Some operations which were done from the instruction
line with a large number of parameters until the discovery of IDE "Integrated Development
Environment" are now made easier by using the MPLAB. Still, our tastes differ, so even today
some programmers prefer the standard editors and compilers from instruction line. In any case,
the written program is legible, and well documented help is also available.

5.1 Installing the program -MPLAB

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Chapter 5 - MPLAB

vtt

CopyiWit Mk mtrihTwh

— . * ■ "i i hi ill ■ *■ i i i ■ li ii i i-E

MPLAB consists of several parts:

- Grouping the files of the same project into one project (Project Manager)

- Generating and processing a program (Text Editor)

- Simulator of the written program used for simulating program function on the microcontroller.

Besides these, there are support systems for Microchip products such as PICStart Plus and I CD (In
Circuit Debugger). As this book does not cover these , they will be mentioned only as options.

Minimal computer requirements for staring the MPLAB are:

PC compatible computer 486 or higher

Microsoft Windows 3.1x or Windows 95 and new versions of the Windows operating system

VGA graphic card

8MB memory (32MB recommended)

20MB space on hard disc

Mouse

In order to start the MPLAB we need to install it. Installing is a process of copying MPLAB files
from the CD onto a hard disc of your computer. There is an option on each new window which
helps you return to a previous one, so errors should not present a problem or become a stressful
experience. Installment itself works much the same as installment of most Windows programs.
First you get the Welcome screen, then you can choose the options followed by installment itself,
and, in the end, you get the message which says your installed program is ready to start.

Steps for installing MPLAB:

1. Moving the Microsoft Windows

2. Put the Microchip CD disc into CD ROM

3. Click on START in the bottom left corner of the screen and choose the RUN option

4. Click on BROWSE and select CD ROM drive of your computer.

5. Find directory called MPLAB on your CD ROM

6. Click on SETUP.EXE and then on OK .

7. Click again on OK in your RUN window

Installing begins after these seven steps. The following pictures explain the meaning of certain

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Chapter 5 - MPLAB

installment steps

MPLM ^S.MLDD Ijiitafrifcn

Welcome screen at the beginning of MPLAB installment

At the very beginning, it is necessary to select those MPLAB components we will be working with
Since we don't have any original Microchip hardware components such as programmers or
emulators, we will only install MPLAB environment, Assembler, Simulator and the instructions.

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Chapter 5 - MPLAB

MPLAB v5.00.00 Installation

Select Components

Choose which components to install by checking the boxes
below.

W MPLAB IDE Files

|7 MPASM/MPLINK/MPUB Files

— MPLAB -SIM Simulator Support Files

r MPLAB -ICE Emulator Support Files

r PI CM ASTER Emulator Support Files

I - PRO MATE Support Files

r PICS TART Plus Support Files

rJMJr^^
17 Help Files

Disk Space Required:
Disk Space Remaining:

2532 k
7321 k
4886 k
3828 k
1198k

508 k

157 k

245 k

5134 k

1 9873 k
2074441 k

< Back

Next>

Cancel

Selecting components of MPLAB developing environment

As it is assumed you will work in Windows 95 ( or a newer operating system), everything in
connection with DOS operating system has been taken out during selection of assembler
language. However, if you still wish to work in DOS, you need to deselect all options connected
with Windows, and choose the components appropriate for DOS.

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Chapter 5 - MPLAB

MPLAB v5.00.00 Installation

Select Language Components

Choose which components to install by checking the boxes
below.

— MPASM for Windows 834 k

T MPASM for DOS 579 k

W MPASM Header Files, Samples, and Templates 1 999 k

W M PLI N KM PLI B for Windows95 1 586 k

M PLI N K/M PLI 8 for Windows 3. 1 /D S 21 50 k

fy Processor Linker Scripts 173 k

Disk Space Required:
Disk Space Remaining:

17144 k
20771 70 k

< Back

Next>

Cancel

Selecting the assembler and the operating system

Like any other program, MPLAB should be installed into some directory. This option can change
into any directory on any hard disc of your computer. If you don't have a more pressing need, it
should be left at selected place.

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Chapter 5 - MPLAB

MPLAB v5.00.00 Installation

Select Destination Directory

Please select the directory where the MPLAB v5.00.00 files are
to be installed.

C:\Program Files\MPLAB

Browse

< Back

Next>

Cancel

Choosing the directory where MPLAB will be installed

Users who have already had MPLAB (older version than this one) need the following option.
The purpose of this option is to save copies of all files which are modified during a changeover to a
new MPLAB version. In our case we should leave selected NO because of presumption that this is
your first installment of MPLAB on your computer.

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Chapter 5 - MPLAB

MPLAB v5.00.00 Installation

Backup Replaced Files?

This installation program can create backup copies of all
replaced during the installation. Do you want to create
backups of the replaced files?

les

TTTTm . . . . ^

f^No

< Back

Next>

Cancel

Option for users who are installing a new version over an already installed MPLAB

Start menu is a group of program pointers, and is selected by clicking on START option in the
lower left corner of the screen. Since MPLAB will be started from here, we need to leave this
option as it is.

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Chapter 5 - MPLAB

MPLAB v5.00.00 Installation

Add to Start Menu ?

Do you want to create shortcuts to access the installed files?

<?Yes
TNo

< Back

Next>

Cancel

Adding the MPLAB to the start menu

Location that will be mentioned from here on, has to do with a part of MPLAB whose explanation
we don't need to get into. By selecting a special directory , MPLAB will keep all files in connection
with the linker in a separate directory.

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Chapter 5 - MPLAB

Linker Scripts

Linker script Location

Due to the expanded number of linker scripts you may
now install them in their own sub directory. Users with
previous projects may prefer to keep them in the MPLftB
directory for compatibility with existing projects (default).
If you are a new user you may wish to keep these in the
\LKR sub directory.

r - Install files to MPLAB install directory
C flnstaii fiies to MP

< Back

Next>

Cancel

Determining a directory for linker files

Every Windows program has system files usually stored in a directory containing Windows
program. After a number of different installments, the Windows directory becomes overcrowded
and too big. Thus, some programs allow for their system files to be kept in same directories with
programs. MPLAB is an example of such program, and the bottom option should be selected.

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Chapter 5 - MPLAB

Select System Files

Would you like to install system DLL files to your
\Windows\Sys directory? If you are running MPLAB
installed on a common network, you may not be
allowed to write files to this directory. If you do not
install them in the \Windows\Sys directory, they
be put in the same directory as MPLAB.

C Install files to \Windows\Sys

(? Install files to MPLAB install directory

< Back

Next>

Cancel

Selecting a directory for system files

After all of the above steps, installment begins by clicking on 'Next'.

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Chapter 5 - MPLAB

MPLAB v5.00.00 Installation

Ready to Install!

You are now ready to install the MPLAB v5.00.00.

Press the Next button to begin the installation or the Back
button to reenter the installation information.

< Back

Next>

Cancel

Screen prior to installment

Installment doesn't take long, and the process of copying the files can be viewed on a sma
window in the right corner of the screen.

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Chapter 5 - MPLAB

£ MPL*D ykWuOO Inst^jtk^v^ff:^^^

_j_j__

I installment flow

After installment is completed, there are two dialog screens, one for the last minute information
regarding program versions and corrections, and the other is a welcome screen. If text files
(Readme.txt) have opened, they need to be closed.

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Chapter 5 - MPLAB

MPLAB v5.00.00 Installation

View README Files?

Each installed component of MPLAB has an associated
README file that contains important information, such as
device support and known issues.

Would you like to view these files now?

CTYes
r No

Please reuiew these files before contacting
Customer Support.

Next>

Cancel

Last minute information regarding program versions and corrections

By clicking on Finish, installment of MPLAB is finished.

page

Table of
contents

Chapter
overview

Next page ►

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Chapter 5 - MPLAB

Table of
contents

Chapter
overview

Next page ►

5.2 MPLAB

Following the installment procedure, you will get a screen of the program itself. As you can see,
MPLAB looks like most of the Windows programs. Near working area there is a "menu" (upper blue
colored area with options File, Edit. .etc.), "toolbar" (an area with illustrations the size of small
squares), and status line on the bottom of the window. There is a rule in Windows of taking some
of the most frequently used program options and placing them below the menu, too. Thus we can
access them easier and speed up the work. In other words, what you have in the toolbar you also
have in the menu.

-MF'LjSD

Efr fto.«i Idt Qetug QdIw I«l> wrehw N^,

■ |5]>:|

B 1 jT| j] j] |T|^]SB ISSB^H BHBIH1 IT

5O0GQ

PiCierSi K.QrfO ".-.fMBj—Mfcc " jBkOn EO HMIfc JUwr

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Chapter 5 - MPLAB

The screen after starting the MPLAB

The purpose of this chapter is for you to become familiar with MPLAB developing environment and
with basic elements of MPLAB such as:

Choosing a developing mode

Designing a project

Designing a file for the original program

Writing an elementary program in assembler program language

Translating a program into executive code

Starting the program

Opening a new window for a simulator

Opening a new window for variables whose values we watch (Watch Window)

Isaving a window with variables whose values we are watching

Setting the break points in a simulator (Break point)

Preparing a program to be read in a microcontroller can boil down to several basic steps:

a Previous Table of Chapter npy1- nanp t

^ page contents overview '^ CAL M^yc w

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Chapter 5 - MPLAB

Table of
contents

Chapter
overview

Next page ►

5.3 Choosing the development mode

Setting a developing mode is necessary so that MPLAB can know what tools will be used to
execute the written program. In our case, we need to set up the simulator as a tool that's being
used. By clicking on OPTIONS---> DEVELOPMENT MODE, a new window will appear as in the
picture below:

Development Mode

onfiguration ] Power
toois 1 Ports

4 None (Editor Only)
> MPLAB -SIM Simulator

M Pi All • ! C £: I: $ft«l*Uor
:> i CM ASTER £muk£m

\
/

"ivv.tti"

"LAB -ID) O^bn^er

] Break Options
Memory

Processor:

PIC1GF84

Inquire

Details.

Cancel

Apply

Help

Setting a developing mode

We should select the 'MPLAB-SIM Simulator' option because that is where the program will be
tried out. Beside this option, the 'Editor Only' option is also available. This option is used only if we
want to write a program and using a programmer write' hex file' in a microcontroller. Selection of
the microcontroller model is done on the right hand side. Since this book is based on the
PIC16F84, this model should be selected.

Ordinarily when we start working with microcontrollers, we use a simulator. As the level of
knowledge increases, program can be written in a microcontroller right after translation. Our
advice is that you always use the simulator. Though program will seem to develop slower, it will
pay off in the end.

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Chapter 5 - MPLAB

a Previous Table of Chapter Npy1 - n - np k

^ page contents overview M c| y c r

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Chapter 5 - MPLAB

Table of
contents

Chapter
overview

Next page ►

5.4 Designing a project

In order to start writing a program you need to create a project first. By clicking on PROJECT -->

NEW PROJECT you are able to name your project and store it in a directory of your choice. In the

picture below, a project named 'proba.pjt' is being created and stored in c:\PIC\PROJEKTI\

directory.

This directory is chosen because authors had such directory set up of on their computer. Generally

speaking, directory with files is usually placed in a larger directory whose name is unmistakably

associated with its contents.

New Project

File Name:

proba.pjt

List Files of Type:

Directories:

| Project Files [ x -pjt] ~^_

c:\pic\projekti

Cancel

c:\

t3 P" c

projekti

Help

Drives:

i==J c: zombil

Opening a new project

After naming the project, click on OK. New window comes up as in the next picture,

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Chapter 5 - MPLAB

Edit Project

Project

Target Filename

proba.hex

Include Path

[

Library Path

Linker Script Path

Development Mode:

Language Tool Suite:
r Project Files

MPLAB-SIM1GF84

Microchip

proba [.hex]

Cancel

Help

Add Node

Copy Node.

Delete Node

Build Node

Node Properties.

Change...

Adjusting project elements

Using a mouse click on "proba [.hex]" which activates 'Node properties' option in the bottom right
corner of a window. By clicking on it you get the following window.

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Chapter 5 - MPLAB

N_da Frcpecli&s

Hex Fermat

Error File

List File

CrEj^s-refereiice File
Warning level

INHX8M . • INHX8S I . INHX3Z
On a OH

. : Off

Case scnsilivity
Macro expansion

Default radix

Tab size

jtfOff

i warnJ-err
. Off

: Off

DEC

err

. [OCT

CcimimaTid Line

/_inhxsm /e* ji+ /*- /c+ ;ti /piGF34

AddMorwj Command Line Options

Defining parameters of MPASM assembler

From the picture we see that there are many different parameters. Each kind corresponds to one
parameter in "Command line" term. As memorizing these parameters is very uncomfortable, even
forbidding for beginners, graphic adjustment has been introduced. From the picture we see which
options need to be turned on. By clicking on OK we go back to previous window where "Add node"
is an active option. By clicking on it we get the following window where we name our assembler
program. Let's name it "Proba.asm" since this is our first program in MPLAB.

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Chapter 5 - MPLAB

Add Node

File name:

proba asmj

Folders:
c:\pic\projekti

f3 projekti

List files of type:

| Source Mies [*.c; x .asm]

Drives:

i=J c: zombil

TTx

Cancel

Help

Network.

Opening a new project

By clicking on OK we go back to the starting window where we see added an assembler file,

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Chapter 5 - MPLAB

Edit Project

Project

Target Filename

proba.hex

Include Path

[

Library Path

Linker Script Path

Development Mode:

Language Tool Suite:
r Project Files

MPLAB-SIM1GF84

Microchip

proba [.hex]
proba [.asm]

Cancel

Help

Change...

Add Node

Copy Node.

Delete Node

Build Node

Properties.

Assembler file added

By clicking on OK we return to MPLAB environment.

Table of
contents

Chapter
overview

Next page ►

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Chapter 5 - MPLAB
© Copyright 1999. mikroElektronika. All Rights Reserved. For any comments contact webmaster .

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Chapter 5 - MPLAB

Table of
contents

Chapter
overview

Next page ►

5.5 Designing a new assembler file (writing a new

program)

When "project" part of the work is finished, we need to start writing a program. In other words,
new file must be opened, and will be named "proba.asm". In our case, file has to be named
"proba.asm" because in projects which have only one file (such as ours), name of the project and
name of the original file have to be the same.

New file is opened by clicking on FILE>NEW. Thus we get a text window inside MPLAB work space

=1""MPLM ■CAPII^PnOJEKliyTOJBA.PJT

£te Px-ki L-y Letug r\c_-yrn., : _:j.^ : r, : rj : _»jw Met,

THE]

r^;_]_»r_)£

l_M_ld ^)_J 33

; fcfl No-*v» iN-i Pt;it":-i o:(MXi w.(W» --rdcc [:■ On S~ 4 MHz Debug

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Chapter 5 - MPLAB

New assembler file opened

New window represents a file where program will be written. Since our assembler file has to be
named "proba.asm", we will name it so. Naming is done (as with all Windows programs) by
clicking on FILE>SAVE AS. Then we get a window like the following picture.

Save File As

File Name:

proba.asm

List Files of Type:
Source Mies [*.c;*.asm] w \

Directories:
c:\pic\projekti

_j cA
__J projekt

Drives:

i==l c: zombil

Cancel

Help

r UNIX format
J Iv* Keep backup

Network.

Naming and saving a new assembler file

When we get this window, we need to write 'proba.asm' below 'File name:', and click on OK. After
that, we will see 'proba.asm' file name at the top of our window.

Table of
contents

Chapter
overview

Next page ^

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Chapter 5 - MPLAB

page

Table of
contents

Chapter
overview

Next page ►

5.6 Writing a program

Only after all of the preceding operations have been completed can we start writing a program.
Since a simple program has already been written in "Assembly Language Programming" section of
the book, so we will use that same program here, too.

Program: Proba.asm

;Program for initialisation of port B and setting its pins to
; state of logic one

;Yersion: 1.0 Date: 25.04.2000 MCU: PIC16F84 Written by: Petar
; Petrovic

; Declaration and configuration of processor

PROCESSOR 16F84

# include "pi 6f 8 4 . inc " ; Processor title

CP OFF £ 1a)DT OFF £ PWRTE ON £ XT OSC

; Reset vector

; Go to the beginning of the main

; program

; Interrupt vector

; Interrupt routine does not exist

# include "bank. inc" ; Macros EANKU and BANKl
; Beginning of the main program

__CONFIG

org
goto

0x00
Main

org
goto

0x04
Main

Main

BANKl

movlw 0x00

movTAif TRISB
BANK0

movlw OxFF

movTAif PORTB

; Select memory bank 1

; Port B pins are output
; Select memory bank

; Set all ones to port B

Chapter 5 - MPLAB

Petlja goto Petlja
end

; sec a_LJ_ ones uo port rs

; Program stays in the loop

; Necessary marking the end of a

; program

Program has to be copied to a window that's opened, or copied from a disc, or taken from
MikroElektronika Internet presentation using options copy and paste. When the program is copied
to "proba.asm" window, we can use PROJ ECT -> BUI LD ALL command (if there were no errors),
and a new window will appear as in the next picture.

HI Build RpjsuJU

Building PROBA.HEK...

Compiling PFtQBA.ASK:

Command line: "C:\PR0GRA~1\MPLABWftSKWIH.EKE /aINHXSM /e* /l* /x- /c+ /t1 i

Message [3 02] C:\PIC\PROJEKTI\PROBA.ASM 22 : Register in operand not in bank

Build completed successfully.

ft .<: ..ft. .ft. .ft. .ft. ft. ft. ft. ft: : : : : ft: -: : : ft: : : : * : : : *: : : : ■>: : : : : : :- :ft -: : :- ■>:• :>• : : :- : : :- : : :-

■X Xv A .<-. A; A: .<: A: A: AA -X -'A -X -X -X -X -X -X -X -X -X -X- -X- -X- -X- X- X- X- X-

Window with messages following a translation of assembler program

We can see from the picture that we get "proba.hex" file as a result of translation process, that
MPASMWIN program is used for translation, and that there is one message. In all that information,
the last sentence in the window is the most important one because it shows whether translation
was successful or not. 'Build completed successfully' is a message stating that translation was
successful and that there were no errors.

In case an error shows up, we need to double click on error message in 'Build Results' window.
This will automatically transfers you to assembler program and to the line where the error is.

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Chapter 5 - MPLAB

page

Table of
contents

Chapter
overview

Next page ►

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Chapter 5 - MPLAB

Table of
contents

Chapter
overview

Next page ►

5.7 MPSIM Simulator

Simulator is part of MPLAB environment which provides a better insight into the workings of a
microcontroller. With the help of a simulator, we can watch current variable values, register values
and status of port pins. Truthfully, simulator does not have the same value in all programs. If a
program is simple (like the one given here as an example), simulation is not of great importance
because setting port B pins to logic one is not a difficult task. However, simulator can be of great
help with more complicated programs which include timers, different conditions where something
happens and other similar requirements (especially with mathematical operations). Simulation, as
the name indicates "simulates the work of a microcontroller". As microcontroller executes
instructions one by one, simulator is conceived - programmer moves through a program step by
step (line by line) and follows what goes on with data within a microcontroller. When writing is
completed, it is a good trait if programmer first checks his program in a simulator, and then tries
it out in a real situation. Unfortunately, as with many other good habits, man avoids this one too,
more or less. Reasons for this are partly personality, and partly lack of good simulators.

First thing we need to do, as we would in a real situation, is to reset a microcontroller with DEBUG
> RUN > RESET command. This command results in bold line positioned at the beginning of a
program, and program counter is positioned at zero which can be seen in status line (pc: 0x00).

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Chapter 5 - MPLAB

MPLAB - C:\PIC\PROJ EKTI\PROBA.PJT

File Project Edit Debug Picstart Plus Options

-o-

Tools Window Help

Run

Execute
Simulator Stimulus

Center Debug Location

Break Settings...
Trace Settings...
Trigger In/Out Settings...
Trigger Output Points...
Clear All Points...

overage

r Settings...

Clear Program Memory... Ctrl+S hif t+F2
System R eset Ctrl+S hif t+F3

Power-0 n-R eset. . . Ctrl+S hif t+F5

itinclude "bank.inc"

Halt

Halt Trace

Animate

Step

Step Over

Shift+F5

Ctrl+F9

Update All Registers
Change Program Counter...

###*#

eset vector

;

terapt uector

ma interapt rutine

; Pomocne datoteke

Main

; Pocetak proqrana

]SC

Beginning of program simulation, resetting a microcontroller

One of the main characteristics of a simulator is the ability to view register status within a
microcontroller. These registers are also called special function registers, or SFR registers.
We can get a window with SFR registers by clicking on WINDOW- >SPECIAL FUNCTION
REGISTERS, or on SFR icon.

Beside SFR registers, it is useful to have an insight into file registers. Window with file registers
can be opened by clicking on WINDOW->FILE REGISTERS.

If there are variables in the program, it is good to watch them, too. To each variable is assigned
one window (Watch Windows) by clicking on WINDOW- >WATCH WINDOWS.

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Chapter 5 - MPLAB

SFR Registers Window
Name of the
current project

Menu line
Toolbar line

Assembler program

Window for watching
variable status

Status line
File Register Window

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40*4400*
40*4400*
4AM44M
?uljjuuj.

?ULJ JUUJ-
7UL J JUL!.!-

f* H-c=ili™ ViVi-t-B

USE

■li

ijrj 41 K W *«■ 45 » PF d f ? bib *p » « t;

I0f* qq H H II |Q H H - IP M P4 PP 4J 14 0* 4P

IQ1Q pp 4P H p» |p 44 pt PP IP *t P* PP 44 14 PI CP

IQQ4 4D « M DMD H H 4t> IP 44 » PP 44 44 P* 4P

4H4 DO 44 14 0* 40 44 Ot 00 40 44 04 PP 4* 4* Pt IP

10^-1 00 40 14 0* 10 4* 0* 00 40 44 04 00 4* 14 01 40

WCdl

i 3+ >fi JJ-sW^Nii PC1BF34 pdMD IhWO;-:*;? .&L(h|Eii [AWx |Di^

Simulator with open windows for SFR registers, file registers and variables.

The next command in a simulator is DEBUG>RUN>STEP which starts our movement through the
program. The same command could have been assigned from a keyboard with <F7> key
(generally speaking, all significant commands have keys assigned on the keyboard).
By using the F7 key, program is executed step by step. When we get to a macro, file containing a
macro is opened (Bank.inc), and we proceed to go through a macro. In a SFR registers window we
can observe how W register receives value OxFF and delivers it to port B. By clicking on F7 key
again, we don't achieve anything because program has arrived to an "infinite loop". Infinite loop is
a term we will meet often. It represents a loop from which a microcontroller can not get out until
interrupt occurs (if it is used in a program), or until a microcontroller is reset.

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Chapter 5 - MPLAB

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Chapter 5 - MPLAB

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5.8 Toolbar

Since MPLAB has more than one component, each of the components has its own toolbar.
However, there is a toolbar which is some sort of a combination of all toolbars, and can serve as a
common toolbar. This toolbar is enough for our needs, and it will be explained in more detail. In
the picture below, we can see a toolbar we need with a brief explanation of each icon. Because of
the limited format of this book, this toolbar is shown as a hanging toolbar. Generally, it is placed
horizontally below the menu, over the entire length of the screen.

Changing a toolbar

Saving a project

Cutting a part
of the text out

Pasting a part
of the text

Start program
execution

Step by step program
execution

Microcontroller reset

RAM memory Window

Variables Window

u jk

_jji

HUM

i 1 1 1 1 1 i J

Ran

M\\

SFR

(CO)

Opening the project

Searching for a
part of the text

Copying a part
of the text

Saving the
assembler file

Stop program
execution

Skip conditions

RAM memory
Window

SFR registers
Window

Repeat translation of
the entire project

Universal toolbar with brief explanations of the icons

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Chapter 5 - MPLAB

Meaning of icons in a toolbar

If the current toolbar for some reason does not respond to a click on this icon, the next
one appears. Changeover is repeated so that on the fourth click we will get the same
toolbar again.

Icon for opening a project. Project opened in this way contains all screen adjustments
and adjustment of all elements which are crucial to the current project.

Icon for saving a project. Saved project will keep all window adjustments and all
parameter adjustments. When we read in a program again, everything will return to the
screen as when the project was closed.

Searching for a part of the program, or words is operation we need when searching
through bigger assembler or other programs. By using it, we can find quickly a part of
the program, label, macro, etc.

Cutting a part of the text out. This one and the following three icons are standard in all
programs that deal with processing textual files. Since each program is actually a
common text file, those operations are useful.

Copying a part of the text. There is a difference between this one and the previous
icon. With cut operation, when you cut a part of the text out, it disappears from the
screen (and from a program) and is copied afterwards. But with copy operation, text is
copied but not cut out, and it remains on the screen.

When a part of the text is copied, it is moved into a part of the memory which serves
for transferring data in Windows operational system. Later, by clicking on this icon it
can be 'pasted' in the text where the cursor is.

Saving a program (assembler file).

Start program execution in full speed. It is recognized by appearance of a yellow status
line. With this kind of program execution, simulator executes a program in full speed
until it is interrupted by clicking on the red traffic light icon.

Stop program execution in full speed. After clicking on this icon, status line becomes
gray again, and program execution can continue step by step.

Step by step program execution. By clicking on this icon, we begin executing an
instruction from the next program line in relation to the current one.

Skip requirements. Since simulator is still a software simulation of real work, it is
possible to simply skip over some program requirements. This is especially handy with
instructions which are waiting for some requirement following which program can
proceed further. That part of the program which follows a requirement is the part that's
interesting to a programmer.

__1

tatm

Resetting a microcontroller. By clicking on this icon, program counter is positioned at
the beginning of a program and simulation can start.

Ron

By clicking on this icon we get a window with a program, but this time as program
memory where we can see which instruction is found at which address.

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Chapter 5 - MPLAB

1 With the help of this icon we get a window with the contents of RAM memory of a
1 microcontroller.

SFR

By clicking on this icon, window with SFR register appears. Since SFR registers are used
in every program, it is recommended that in simulator this window is always active.

lOOj

If a program contains variables whose values we need to keep track of (ex. counter), a
window needs to be added for each of them, which is done by using this icon.

When certain errors in a program are noticed during simulation process, program has

tn ho rnrrorforl Qinro cimiilalrir ncoc HFY filo ac ifc inniil - en \a/o noorl tri franclafo ^

■<ii

1 UVy WV- V-Vy 1 1 V.V.tV,Wi ""' IV - V - Jll 1 lUIULUI \_I_>V_._J 1 1 l_/\ IIIV> V-I»J ItJ II IfJUL, JV VV V- 1 IV.V-W UV-» Ul Ul 1 _> 1 «_4 LV< C*

program again so that all changes would be transferred to a simulator. By clicking on

uiib iluii, enure prujeLi ib u cnibidieu dyani, ciiiu wtj yet trie MtwtjbL veibiuu ui ncA ine

for the simulator.

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Chapter 6 - Samples

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CHAPTER 6

Samples

Introduction

6.1 Supplying the microcontroller

6.2 Macros used in programs

q Macros WAIT, WAITX
q Macro PRINT

6.3 Samples

LED diodes

Keyboard

Optocoupler

r Optocouplering the input lines
r Optocouplering the output lines
Relays

Generating a sound
Shift registers

r Input shift register
r Output shift register
q 7-segment Displays (multiplexing)
q LCD display
q 12-bit AD converter
q Serial communication

I ntroduction

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Chapter 6 - Samples

Examples given in this chapter will show you how to connect the PIC microcontroller with other
peripheral components or devices when developing your own microcontroller system. Each
example contains detailed description of the hardware part with electrical outline and comments
about the program. All programs can be taken directly from the from copied from
'MikroElektronika' internet presentation.

6.1 Supplying the microcontroller

Generally speaking, the correct voltage supply is of utmost importance for the proper functioning
of the microcontroller system. It can easily be compared to a man breathing in the air. It is more
likely that a man who is breathing in fresh air will live longer than a man who lives in a polluted
environment.

For a proper function of any microcontroller, it is necessary to provide a stable source of supply, a
sure reset when you turn it on and an oscillator. According to technical specifications by the maker
of PIC microcontroller, supply voltage should move between 2.0V to 6.0V in all versions. The
simplest solution to the source of supply is using the voltage stabilizer LM7805 which gives stable
+5V on its output. One such source is shown in the picture below.

Transformer

220V-

Cl = 22pF ? C2 = lLiUiiF,
C3= 10pF ? R= IK

.■■r?

In order to function properly, or in order to have stable 5V at the output (pin 3), input voltage on
pin 1 of LM7805 should be between 7V through 24V. Depending on current consumption of device
we will use the appropriate type of voltage stabilizer LM7805. There are several versions of
LM7805. For electricity consumption of up to 1A we should use the version in TO-220 housing with
the capability of additional cooling. If the total consumption is 50mA, we can use 78L05 (stabilizer
version in small TO - 92 packaging for electricity of up to 100mA).

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Chapter 6 - Samples

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Chapter 6 - Samples

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6.2 Macros used in programs

Examples given in the following sections of this chapter often use macros WAIT, WAITX and
PRINT, so they will be explained in more detail.

Macros WAIT, WAITX

File Wait.inc contains two macros WAIT and WAITX. Through these macros it is possible to assign
time delays in different intervals. Both macros use the overflow of counter TMRO as a basic
interval. By changing the prescaler we can change the length of the overflow interval of the
counter TMRO.

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Chapter 6 - Samples

IlaXro: UAIT.

INC

;***** Declaring constants
CONSTANT PRESCstd = .1

*****

;standard prescaler val

ue for THRO

;**** * Macros

*****

UAIT

macro
movlu

call
endm

timeconst_l
time const 1
UAITs td

UAITX macro

timeconst_2,

PRESCext

movli.j

time const 2

movuf

UCYCLE

;set the delay time period

movliij

PRESCext

;urite specific prescaler value

call

UAIT_x

endm

;***** Subpro

grams *****

UAITs td

mowf

UCYCLE

;set the delay time period

movlu

PRESCstd

;T.Trite specific prescaler value

UAIT_

clrf
BAHKl

THRO

mowf

0PTI0N_REG

;assign the prescaler to THRO timer

BAHKO

UAITa bcf

IHTC0N,T0IF

;erase THRO Overflow Flag

UAITt

i btfss

IHTC0N,T0IF

; check whether it is erased, skip if
;isn' t

goto

UAITb

;Uait loop

decfss

UCYCLE, 1

;repeat the loop if delay period has
;run out

no t

goto

UAITa

RETURH

If we use the oscillator (resonator) of 4MHz, for prescaler values 0, 1 and 7 that divide the basic
clock of the oscillator, the interval followed by an overflow of timer TMRO will be 0.512, 1.02 and
65.3 mS. Practically, that means that the biggest delay that can result would be 256x65. 3mS
which is equal to 16.72 seconds.

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Chapter 6 - Samples

Prescaler

Divisor

Overflow

b'00000000

1:2

0.512ms

b'OOOOOOOl'

1:4

1.02 ms

b'OOOOOlll'

1:256

65.3 ms

In order to use macros in the main program it is necessary do declare variables wcycle and
prescWAIT as has been done in examples which follow in this chapter.
Macro WAIT has one argument. The standard value assigned to prescaler of this macro is 1
(1.02mS), and it can not be changed.

WAIT timeconst_l

timeconst_l is number from to 255. By multiplying that number with the overflow time period
we get the total amount of the delay: Tl ME=timeconst_l x 1.02mS.

Example: WAIT .100

Example shows how to make a delay of 100x1. 02mS, or total of 102mS.

Unlike macro WAIT, macro WAITX has one more argument that can assign prescaler value. Macro
WAITX has two arguments:

Timeconst_2 is number from to 255. By multiplying that number with the overflow time period
we get the total amount of the delay:
TIME=timeconst_l x 1.02mS x PRESCext

PRESCext is number from to 7 which sets up the relationship between a clock and timer TMR0.

Example: WAITX .100,7

Example shows how to make a delay of 100x65.3 mS, or total of 653mS.

Macro PRINT

Macro PRI NT is found in Print. inc file. It makes it easy to send a series of data on one of the
output devices such as : LCD, RS232, matrix printer... etc. The easiest way to form a series is by
using a dt (define table) directive. This instruction stores a series of data into program memory as
a group of retlw instructions whose operand is data from the series.

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Chapter 6 - Samples

Macro: PRINT. INC

PRIHT macro Addr, Start, End, Var, Out

Local Next

Local Exit

movlu Start

mowf Var

movf Var,u

call Addr

Local label

Out

movf Var,u

ii i ii In T\ r ] ii ■■

; Is it the enci of r-he series?

; If it is- get out of the loop

; If i" isn't, set the Pointer to the next member

; of the- penes

; Repeat the loop

Address of the first member in the series

Pointer -> U reg.

Series ( XJ" reg. ) -> W reg.

Data is in U reg.

Display data on the output device

Exit

> . J

btfsc

j.-.jiTTJi:,

r ■

go 3:

Exit

mcf

'. r ar , f

goto

endm

How one such sequence is formed by using dt instruction is shown in the following example:

org 0x00
goto Main

Series movwf PCL

Seriesl dt "this is 'ASCII 1 series"

Series2 dt "Second series"

End

Main

movlw . 5
call Series

First instruction after label Main writes the position of a member of the sequence in w register. We
jump with instruction call onto label series where position of a member of the sequence is added
to the value of the program counter: PCL=PCL+W. Next we will have in the program counter an
address of retlw instruction with the desired member of the sequence. When this instruction is
executed, member of the sequence will be in w register, and address of the instruction that
executed after the call instruction will be in the program counter. End label is an elegant way to
mark the address at which the series ends.

Macro PRINT has five arguments:

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Chapter 6 - Samples

PRINT macro Addr, Start, End, Var, Out

Addr is an address where one or more sequences (which follow one after another) begin.

Start is an address of the first member of the sequence

End is an address where the sequence ends

Var is the variable which has a role of showing (pointing ) the members of the sequence

Out is an argument we use to send the address of existing subprograms in working with output

devices such as : LCD, RS-232 etc.

Example: org 0x00

goto Main

Series movuf PCL

Message dt "mikroElektronika"

End

Main

PRINT Series, Message, End, Pointer, LCDu

Macro PRI NT writes out a series of ASCI I signs for 'MikroElektronika' on LCD display
The sequence takes up one part of program memory beginning at address 0x03.

a Previous Table of Chapter npy1- nanp t

^ page contents overview |>1CAL M^yc w

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Chapter 6 - Samples

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6.3 Samples

LED Diodes

LEDs are surely one of the most commonly used elements in electronics. LED is short for 'Light
Emitting Diode'. When choosing a LED, several parameters should be looked at: diameter, which is
usually 3 or 5 mm (millimeters), working current which is usually about 20mA (It can be as low as
2mA for LEDs with high efficiency - high light output), and color of course, which can be red or
green though there is also orange, blue, yellow....

LEDs must be connected around the correct way, in order to emit light and the current- limiting
resistor must be the correct value so that the LED is not damaged or burn out (overheated). The
positive of the supply is taken to the anode, and the cathode goes to the negative or earth of the
project (circuit). In order to identify each lead, the cathode is the shorter lead and the LED
housing usually has a cut or "flat" on the cathode side. Diodes will emit light only if current is
flowing from anode to cathode. Otherwise, its PN junction is reverse biased and current won't
flow. In order to connect a LED correctly, a resistor must be added in series that will limit the
amount of current through the diode, so that it does not burn out. The value of the resistor is
determined by the amount of current you want to flow through the LED. This can range from 2mA
to 25mA. High-efficiency LEDs can produce a very good output with a current as low as 2mA.

To determine the value of the dropper- resistor, we need to
know the value of the supply voltage. From this we subtract
the characteristic voltage drop of a LED. This value will range
from 1.7v to 2.3v depending on the color of the LED. The
answer is the value of Ur, Using this value and the current we
want to flow through the LED (0.002A to 0.01A) we can work
out the value of the resistor from the formula R=Ur/ I .

+5v

flat

LED

LEDs are connected to a microcontroller in two ways. One is to turn them on with logic zero, and
other to turn them on with logic one. The first is called NEGATIVE logic and the other is called
POSITIVE logic. The normal method is POSITIVE logic. The above diagram shows how they are
connected for POSITIVE logic. Since POSITIVE logic provides a voltage of +5V to the diode and
dropper resistor, it will emit light each time a pin of port B is provided with a logic 1(1 = HIGH
output). NEGATIVE logic requires the LED to be turned around the other way and the cathode

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Chapter 6 - Samples

connected to the positive supply. When a LOW output from the microcontroller is delivered to the
LED and resistor, the LED will illuminate.

5 „.

+5v
-X-

3 _

{

RA2

RA3

RA4T0CKI

HCLR

RA1

RAO

0SC1

0SC2

PIC
Vss 16F84 Vdd

RBOANT

RBI

RB2
RB3

RB7
RBG
RB5
RB4

]

]■

}

1C-

4MHz

33nn
-CZr
33nn

33DH
HZZK

33nn
■1^=1-

33nn
-IZZF
33nn

■5v
J

■JJ LED
"Ft

V* l£D

*<■ LEU

33nn .« leu

= — w —

LEU

LID

33nn .** led

a W —

Connecting LED diodes to PORTB microcontroller

The following example initializes port B as output and sets logic one to each pin of port B to turn
on all LEDs.

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Chapter 6 - Samples

Program: LED. ASH

;***** Declaring and configuring a microcontroller *****

PROCESSOR 16f84
^include rr pl6f84.inc"

CONFIG _CP_0FF & J3DT_0FF & _PT3RTE_0N & JCTJJSC

;***** Structure of program memory *****

ORG

Oxi ii

Ham

00 J

g;^T'.'

; R p.p p r. up n r.n r

H=r?:*irii

ORP - --." ' "OkTJ ^ I" " " V-= ■- - ; _= _ nEe f xOpj£«ve c to x:

cert i H£_f>* ; J Ju 3 " Iff i tflr.r a vm ^> ■ if.ut. _if>

^iVr^^^^r/^OiVl^r'Lrirv^rfir^ 1 ^^ '^: Vvr;

; Beginning ^f program

j pi:ii:xi A i::x:!.tiaii!saticri

; TF.ISA <- ?:cff a' nyx

; lort E initialization

; TF.I?E =:- CxGG elicittif

Eiinci

JUL 0^1 to"

Tix :^ f :

L.:~"f

T? .ISA

mcvl"

CxCC

mcvrf

TF .I?E

EAHEC

lllCrt'lV

Cii: ]"::":

jiiriVJ:'.

TifirtTh

ijui.o loct

End

Tnj ii u.- .iJ I Jn:.1y

; Si.av m the loor

; End of progr;Bia

a Previous
^ page

Table of
contents

Chapter Next page ^

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Chapter 6 - Samples

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Keyboard

Keyboards are mechanical devices used to execute an interrupt or make connections between two
points. They come in different sizes and with different purposes. Keys that are used here are also
called "dip- keys". They are soldered directly onto a printed plate and are often found in
electronics. They have four pins (two for each contact) which give them mechanical stability.

+5v

(

Pull-up resistor

+5v

10k

■ j — i — »

reset

6 --

T_/

RA2

RA3

RMTOCKI

RA1

RAO

OSC1

MCLR pip OSC2
Vss 16F84 Vdd

RBOAWT RB7

RBI
RB2
RB3

RB6
RB5
RB4

□

]

4MHi

1-E-

+5vL

-II-

ii 330R ^

□ — ^=> H-

LETi

Example of connecting keys to microcontroller pins.

Key function is simple. When we press a key, two contacts are joined together and connection is
made. Still, it isn't all that simple. The problem lies in the nature of voltage as an electrical
dimension, and in the imperfection of mechanical contacts. That is to say, before contact is made
or cut off, there is a short time period when vibration (oscillation) can occur as a result of
unevenness of mechanical contacts, or as a result of the different speed in pressing a key (this
depends on person who presses the key). The term given to this phenomena is called SWITCH
(CONTACT) DEBOUNCE. If this is overlooked when program is written, an error can occur, or the
program can produce more than one output pulse for a single key press. In order to avoid this, we
can introduce a small delay when we detect the closing of a contact. This will ensure that the
press of a key is interpreted as a single pulse. The debounce delay is produced in software and the

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Chapter 6 - Samples

length of the delay depends on the key, and the purpose of the key. The problem can be partially
solved by adding a capacitor across the key, but a well-designed program is a much- better
answer. The program can be adjusted until false detection is completely eliminated.
In some case a simple delay will be adequate but if you want the program to be attending to a
number of things at the same time, a simple delay will mean the processor is "doing-nothing" for a
long period of time and may miss other inputs or be taken away from outputting to a display.
The solution is to have a program that looks for the press of a key and also the release of a key.
The macro below can be used for keypress debounce.

HaXro: TESTER. INC

TESTER macro HiLo, Port, Bit, Delay, Address

Loop

Exit

Local Exit
Local Loop
if HiLo ==

btfsc Port, Bit
else

btfss Port, Bit
endif
goto Exit

WAIT Delay

if HiLo ==

btfss Port, Bit
else

btfsc Port, Bit
endif
goto Loop
WAIT Delay

call Address

en dm

; Local labels

; Is the key pressed?

; Is input line LOU?

; Is input line HIGH?

; If key hasn't been pressed, exit the

; macro

; Delay for key debounce

; Is the key released?

; Delay for key debounce

■

; Call the service subprogram

; Exit the macro

; End of macro

The above macro has several arguments that need to be explained:

TESTER macro HiLo, Port, Bit, Delay, Address

HiLo can be '0' or '1' which represents rising or falling edge where service subprogram will be

executed when you press a key.

Port is a microcontroller's port to which a key is connected. In the case of a PIC16F84

microcontroller, it can be PORTA or PORTB.

Bit is port's line to which the key is connected.

Delay is a number from to 255, used to assign the time needed for key debounce detection

contact oscillation - to stop. It is calculated as TIME = Delay x 1ms.

Address is the address where the micro goes after a key is detected. The sub- routine at the

address carries out the required instruction for the keypress.

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Chapter 6 - Samples

Example 1: TESTER 0, PORTA, 3, .100, Testerl_below

Key-1 is connected to RAO (the first output of port A) with a delay of 100 microseconds and a
reaction to logic zero. Subprogram that processes key is found at address of label Testerl_above.

Example2: TESTER 0, PORTA, 2, .200, Tester2_below

Key-2 is connected to RA1 (the second output of port A) with 200 mS delay and a reaction to logic
one. Subprogram that processes key is found at address of label Tester2_below.

The next example shows the use of macros in a program. TESTER. ASM turns LED on and off. The
LED is connected to the seventh output of port B. Key-1 is used to turn LED on. Key-2 turns LED
off.

Program: TESTER. ASH

;***** Declaring and configuring a microcontroller *****

PROCESSOR 16f84

^include rr pl6f 8 4- inc"

CONFIG _CP_0FF & JJDT_0FF £ _PliJRTE_0N £ JCT_0SC

;***** Declaring variables *****

Cblock OxOC
UCYCLE
PRE SC wait
endc

; Beginning of RAH

; Belongs to 'WAIT 1 macro

;***** Structure of program memory *****

; Reset vector

ORG

0x00

goto

Ha in

ORG

0x04

goto

Ha in

; Interrupt vector

; No interrupt routine

^include "bank.inc" ; Assistant files
^include "tester- inc"
# i nc lud e "uai t . inc "

Main

BANK1
movlu
movuf
movlu
movuf
BANK0

Oxff
TRISA
0x00
TRISB

; Beginning of a program

; Port A initialization

; TRISA <- Oxff

; Port B initialisation

; TRISB <- 0x00

clrf P0RTB ; P0RTB <-

Loop

TESTER 0, PORTA, 2, .100, On ; Tester 1

titstfr n_ Pi~iPTi_ i_ _inn_ nff - Tpst-.pr ?

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Chapter 6 - Samples

TESTER

0, PORTA,

.100, On ; Tester 1

TESTER

0, PORTA,

.100, Off ; Tester 2

goto

Loop

bsf

P0RTB,7

; Turn on LED

return

Off

bcf

PORTE,?

; Turn off LED

return

End

; End of program

page

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Chapter 6 - Samples

page

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contents

Chapter
overview

Next page ►

Optocouplers

Optocouplers combine a LED and photo-transistor in the same housing. The purpose of an
optocoupler is to separate two parts of a circuit.

This is done for a number of reasons:

q I nterference. One part of a circuit may be in a location where it picks up a lot of

interference (such as from electric motors, welding equipment, petrol motors etc.) If the
output of this circuit goes through an optocoupler to another circuit, only the intended
signals will pass through the optocoupler. The interference signals will not have enough
"strength" to activate the LED in the optocoupler and thus they are eliminated. To protect a
section of the device. Typical examples are industrial units with lots of interferences which
affect signals in the wires. If these interferences affect the function of control section, errors
will occur and the unit will stop working.

q Simultaneous separation and intensification of a signal. A signal as low as 3v is able
to activate an optocoupler and the output of the optocoupler can be connected to an input
line of a microcontroller. The microcontroller requires an input swing of 5v and in this case
the 3v signal is amplified to 5v. It can also be used to amplify the current of a signal. See
below for use on the output line of a microcontroller for current amplification.

q High Voltage Separation. Optocouplers have inherent high voltage separation qualities.
Since the LED is completely separate from the photo-transistor, optocouplers can exhibit
voltage isolation of 3kv or higher.

Optocouplers can be used as input or output device. They can have additional functions such as
Schmitt triggering (the output of a Schmitt trigger is either or 1 - it changes slow rising and
falling waveforms into definite low or high values). Optocouplers are packaged as a single unit or
in groups of two or more in one housing. They are also called PHOTO INTERRUPTERS where a
spoked wheel is inserted in a slot between the LED and phototransistor and each time the light is
interrupted, the transistor produces a pulse.

Each optocoupler needs two supplies in order to function. They can be used with one supply, but
the voltage isolation feature is lost.

Optocoupler on an input line

The way it works is simple: when a signal arrives, the LED within the optocoupler is turned on,
and it shines on the base of a photo- transistor within the same housing. When the transistor is
activated, the voltage between collector and emitter falls to 0.5V or less and the microcontroller
sees this as a logic zero on its RA4 pin.
The example below is a counter, used for counting products on production line, determining motor

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Chapter 6 - Samples

speed, counting the number of revolutions of an axle etc.

Let the sensor be a micro-switch. Each time the switch is closed, the LED is illuminated. The LED
'transfers' the signal to the phototransistor and the operation of the photo-transistor delivers a
LOW to input RA4 of a microcontroller. A program in the microcontroller will be needed to prevent
false counting and an indicator connected to any of the outputs of the microcontroller will shows
the current state of the counter.

12v

+5v

T^7

§ v T_[

1 0k

[

^ [

RA2 RA1

RA3 RAO

RA4/T0CKI 0SC1

MCLR p|£ 0SC2

Vss 16F84 Vdd

RB0AWT RB7

RBI RB6

RB2 RB5

RB3 RB4

4MHi

1-E-

14 +5v L

]

1C-

]

I nput line optocoupler example

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Chapter 6 - Samples

Hakro : OPTO_UL . ASH

Declaration and ■

ronfi

-**** *

guring a microcontroller *****

PROCESSOR 16f84

^include rr pl6f84.

inc"

CONFIG _CP_0FF

JBDTJJFF & _PliJRTE_0N & _XT_05C

Progr

am memory structure *****

ORG

0x00

■

Reset vector

goto

Main

ORG

0x04

■

1»"

Interrupt vector

goto

Main

■

No int e r r up t r outi ne

# inc 1 ude "b ank . in c "

■

Assistant files

Main

BAHK1

■

Beginning of program

movlw

Oxef

■

Port A initialization

mowf

TRISA

■

TRISA <- Oxff

movlu

0x00

■

port B initialisation

movuf

TRISB

■

TRISB <- 0x00

movlw

b'00110000

■

RA4 -> THRO, PS=1:2

mowf

0PTI0N_REG

■
r

Increment THRO to/ at falling edge

BAHKO

clrf

PORTE!

■

P0RTB <-

clrf

THRO

■

THRO <-

Loop

movf

THRO , w

■

Copy the timer value

movuf

PORTE:

■

to PORTE:

goto

Loop

■

Repeat the loop

End

■

End of program

Optocoupler on an output line

An Optocoupler can be used to separate the output signal of a microcontroller from an output
device. This may be needed for high voltage separation or current amplification. The output of
some microcontrollers is limited to 25mA. The optocoupler will take the low-current signal from
the microcontroller and drive a LED or relay, as shown below:

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Chapter 6 - Samples

+5v

+12v +12v

X^r

RA2
RA3
RA4/T0CKI

HCLR

RA1

RAO

OSC1

OSC2

PIC
Vss 16F84 vdd

RB0ANT
RBI
RB2
RB3

RB7
RBG
RB5
RB4

CNY17

Output line optocoupler example

The program for this example is simple. By delivering a logic '1' to the fourth pin of port A, the
LED will be turned on and the transistor will be activated in the optocoupler. Any device connected
to the output of the optocoupler will be activated. The transistor current-limit is about 250mA.

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Chapter 6 - Samples

page

Table of
contents

Chapter
overview

Next page ►

The Relay

The relay is an electromechanical device, which transforms an electrical signal into mechanical
movement. It consists of a coil of insulated wire on a metal core, and a metal armature with one
or more contacts.

When a supply voltage is delivered to the coil, current will flow and a magnetic field is produced
that moves the armature to close one set of contacts and open another set. When power is
removed from the relay, the magnetic flux in the coil collapses and produces a fairly high voltage
in the opposite direction. This voltage can damage the driver transistor and thus a reverse- biased
diode is connected across the coil to "short-out" the spike when it occurs.

+5v

RA2
RA3

RJWTOCKI
HCCR

RA1

RAO

0SC1

0SC2

PIC

Vss 16F84 Vdd

RBOAWT
RBI
RB2
RB3

RB7
RBG
RB5
RB4

]

4MHz

14+SV 1

ru_T

]

1C-

o -220V
50Hz

Protective
diode

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Chapter 6 - Samples

Connecting a relay to the microcontroller via a transistor

Many microcontrollers cannot drive a relay directly and so a driver transistor is required. A HIGH
on the base of the transistor turns the transistor ON and this activates the relay. The relay can be
connected to any electrical device via the contacts.

The 10k resistor on the base of the transistor limits the current from the microcontroller to that
required by the transistor. The 10k between base and the negative rail prevents noise on the base
from activating the relay. Thus only a clear signal from the microcontroller will activate the relay.

+5v
T 10k

[

- C

[

RA2
RA3

RJWTOCKI
HCCR

PIC

Vss 16F84 Vdd

RBOJIMT

RB1

RB2

RB3

LOAD

+5v

Protective
diode

-220V
50Hz

■o

Rectifier

Optocoupler
supply

Connecting the optocoupler and relay to a microcontroller

A relay can also be activated via an optocoupler which at the same time strengthens the current
from the output of the microcontroller and provides a high degree of isolation. High current
optocouplers usually contain a 'darlington' output transistor to provide high output current.

Connecting via an optocoupler is recommended especially for microcontroller applications, where
motors are activated as the commutator noise from the motor can get back to the microcontroller

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Chapter 6 - Samples

via the supply lines. The optocoupler drives a relay and the relay activates the motor.

The figure below shows the program needed to activate the relay, and includes some of the

already discussed macros.

Program: RELAY. ASH

;***** Declaring and configuring a microcontroller *****

PROCESSOR 16f84

^include "pl6f 84. inc"

_C0NFIG _CP_0FF £ J3DT_0FF & _PTOTE_0N & _XT_0SC

;***** Declaring the variables *****

Cblock OxOC
WCYCLE
PRESCuait
endc

; Beginning of RAH

; Belongs to macros WAIT and UAITX

;***** Declaring the hardware *****

^define RELAY PORTB, 6

; Relay is on the 7th pin of portB

;***** Structure of program memory *****

ORG 0x00
goto Hain

ORG 0x04
goto Hain

# inc 1 ude "b ank .inc"
^include "tester. inc"
^include "wait. inc"

; Reset vector

; Interrupt vector

; No interrupt routine

; Hacros

Hain

BANK1

movlu b' 00010111'

movuf TRISA

movlu 0x00

movuf TRISB

BANK0

clrf PORTIi

; Beginning of program

; Initialization of port A

; TRISA <- 0x17

; Initialization of port B

; TRISB <- 0x00

; PORTB <- 0x00

Loop

TESTER 0, PORTB , 0, .100, On
TESTER 0, PORTB , 1, .100, Off

goto Loop

; Tester 1
; Tester 2

-i.

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Chapter 6 - Samples

■JJ W WW — w w^

bsf RELAY

; Turn the relay on

return

Off

bcf RELAY

; Turn the relay off

return

End

; End of program

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Chapter 6 - Samples

page

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contents

Chapter
overview

Next page ►

Generating a sound

A Piezo diaphragm can be added to an output line of a microcontroller to deliver a whole range of
tones, beeps and signals.

It is important to know there are two main types of piezo sound-emitting devices. One has active
components inside the casing and only requires a DC supply for the "sounder" to emit a tone or
beep. Generally the tones or beeps emitted by these "sounders" or "beepers" cannot be changed -
they are fixed by the internal circuitry. This is not the type we are discussing in this article.
The other type consists of a piezo diaphragm and requires a signal to be delivered to it for it to
function. Depending on the frequency of the waveform, the output can be a tone, tune, alarm or
even voice messages.

In order for them to work we must deliver a cycle consisting of a HIGH and LOW. It is the change
from HIGH to LOW or LOW to HIGH that causes the diaphragm to "dish" (move) to produce the
characteristic "tinny" sound. The waveform can be a smooth change from one value to the other
(called a sinewave) or a fast change (called a SQUARE WAVE). A computer is ideal for producing a
square wave. The square wave delivery produces a slightly harsher output.
Connecting a piezo diaphragm is very simple. One pin is connected to the negative rail and the
other to an output of a microcontroller, as shown in the diagram below. This will deliver a 5v
waveform to the piezo diaphragm. To produce a higher output, the waveform must be increased
and this requires a driver transistor and inductor.

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Chapter 6 - Samples

R.t"2

RA3

RA4T0CKI

RA1

RAO

OSC1

MCLR p|Q QSC2
Vss 16F84 Vdd

RBOAWT RB7

RBI
RB2
RB3

RB6
RB5
RB4

Connecting a piezo diaphragm to a microcontroller

As with a key, you can employ a macro that will deliver a BEEP ROUTINE into a program when
needed.

BEEP macro has two arguments:

freq: frequency of the sound. The higher number produces higher frequency
duration: sound duration. The higher the number, the longer the sound.

Example 1: BEEP OxFF, 0x02

The output of the piezo diaphragm has the highest frequency and duration at 2 cycles per 65.3mS
which gives 130.6 mS

Example2: BEEP 0x90, 0x05

The output of the piezo diaphragm has a frequency of 0x90 and duration of 5 cycles per 65.3mS.
It is best to determine these macro arguments through experimentation and select the sound that
best suits the application.

The following is the BEEP Macro listing:

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Chapter 6 - Samples

Macro: BEEP. INC

Declaring constants

*****

CONSTANT PRESCbeep =

b' 00000111' ; 65,3 ms per cycle

Macros *****

BEEP

macro

movlu

movwf

movlw

call

endm

f re q, duration
f req

BeepJIEMPl
duration
BEEP sub

BEEPinit macro

bcf

BEEPport

BMTK1

bcf

BEEP tr is

BMIKO

endm

Subprograms *****

BEEP sub mowf Beep_TEHP2

■

Set the value of sound duration

clrf

THRO

■

Initialize the counter

bcf

BEEPport

BANK1

bcf

BEEPport

movlu

PRESCbeep

■

Set the prescaler for THRO

movwf

OPTION REG

OPTION <- XJ

BAHKO

BEEPa

bcf

IMTC0N,T0IF

■

Erase the THRO Overflow Flag

BEEPb

bsf

BEEPport

call

B_Uait

■

Duration of logic '1'

bcf

BEEPport

call

B_Uait

Duration of logic '0'

btfss

INTC0N,T0IF

■

1»"

Check the THRO overflow flag

goto

BEEPb

■

Skip of it is set

decf sz

Beep_TEHP2,l

Is the Beep_TEHP2 = ?

goto

BEEPa

■

If not, jump to BEEP again

RETURN

B_Uait

movfw

movwf

Beep_TEHPl
Beep_TEHP3

B_TJai ta de c f s z Be ep_TEHP 3 ,

goto

B_Uaita

RETURN

The following example shows the use of a macro in a program. The program produces two

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Chapter 6 - Samples

melodies which are obtained by pressing Tl or T2. Some of the previously discussed macros are
included in the program.

Program: BEEP . ASH

-***** Declaring and configuring a microcontroller *****

PROCESSOR 16f84
^include rr pl6f84.inc rr

CONFIG CP OFF & UDT OFF & I'T.JE.TE ON & XT OSC

;***** Declaring variables *****

Cblock OxOC

TUCYCLE

PRESCuait

Beep_TEHPl

Beep_TEHP2

Beep_TEHP3

endc

;***** Declaring the hardware *****

; Beginning of RAH

; Belongs to 'WAITX 1 macro

; Belongs to 'BEEP' macro

#define BEEPport PORTA, 3
#define BEEPtris TRISA,3

; Port and pin for pieso diaphragm

;***** Structure of program memory *****

ORG

0x0

goto

Hain

ORG

0x0 4

goto

Hain

^include "bank. inc"

^include rr teste r . inc "

# in elude "wait. inc"

^include "beep. inc"

BANK1

movlw b' 00010111

mo wf TRI SA

BANK0

BEEPinit

; Reset vector

; Interrupt vector

; No interrupt routine

; Assistant files

Beginning of the program

Port A initialization
TRISA <- 0x17

Beeper initialisation

Loop

Playl

TESTER 0, PORTA, 0, .100, Playl ; Button 1
TESTER 0, PORTA, 1, .100, Play2 ; Button 2
goto Loop

BEEP OxFF, 0x02
BEEP 0x90, 0x05

j~, _

j~, j~.

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Chapter 6 - Samples

JJIdid 1 UA1 1 j

t JJ\*Ji^

BEEP 0x90,

0x05

BEEP OxCO,

0x03

BEEP OxFF,

0x03

; First melody

return

Play2

BEEP Oxbb,

0x02

BEEP 0x87,

0x05

BEEP 0xa2,

0x03

BEEP 0x98,

0x03

; Second melody

return

End

; End of program

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Chapter 6 - Samples

Table of
contents

Chapter
overview

Next page ►

Shift registers

There are two types of shift registers: input and output. I nput shift registers receive data in
parallel, through 8 lines and then send it serially through two lines to a microcontroller. Output
shift registers work in the opposite direction; they receive serial data and on a "latch" line
signal, they turn it into parallel data. Shift registers are generally used to increase the number of
input-output lines of a microcontroller. They are not so much in use any more though, because
most modern microcontrollers have a large number of input/output lines. However, their use with
microcontrollers such as PIC16F84 can be justified.

Input shift register 74HC597

Input shift registers transform parallel data into serial data and transfer it to a microcontroller.
Their working is quite simple. There are four lines for the transfer of data: clock, latch, load and
data. Data is first read from the input pins by an internal register through a 'latch' signal. Then,
with a 'load' signal, data is transferred from the input latch register to the shift register, and from
there it is serially transferred to a microcontroller via 'data' and 'clock' lines.

Zi
Q_

i— A

D
E
F
G
L-H

15
1

2
3
4
5
6
7

Latch -^

Clock
Load^-

Input

latch

Shift
register

£ Serial
output

An outline of the connection of the shift register 74HC597 to a micro, is shown below.

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Chapter 6 - Samples

Connector

o
o
■0
o
o
o
o
o

—nixru-LTLrLTLr

+S , - ,

■[
■[
■[

■[

Pln1 Vcc J-

PIp2

PIpC ]

PlnJ Swlsklulj]

s«ti|skl li
pjulvlp

P|n4
PIpS
PlnG
PIp7
Vss S«f1|skl IzIjET

_kr

r««

D- 3 "

74HC597

+9/

■OK

■C

■c

■f]

T_J

RA2

RA3

RA4iT0CKI

HCLR

RA1

RAD

0SC1

0SC2

PIC
vss 16F84 vcu

RBOJIMT

REM

RB2
RB3

RB7
RB6
RB5
RB4

1-=-

Ml-

M±

-II-

-ii-

D — c

33DH

□ — -=»

33DH
-I »-

33nn

-i 1-

33DH

33nn

■CZH

33Dl _ l

-l=h

+9/

L* HE

** LED

LID

■JJ Lin

"Ft

LID

* * LED

■JJ LED
"F1

How to connect an input shift register to a microcontroller

In order to simplify the main program, a macro can be used for the input shift register. Macro
HC597 has two arguments:

HC597 macro Var, Varl

Var variable where data from input pins is transferred
Varl loop counter

Example: HC597 data, counter

Data from the input pins of the shift register is stored in data variable. Timer/ counter variable is
used as a loop counter.

Macro listing:

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Chapter 6 - Samples

Hakro: HC597.INC

macro

Var ,Varl

HC597

Local

Loop

■

local label

movlu
movuf

.8
Varl

■
■

transfer eight bits
c ounte r ini t i al i z a ti on

bsf
nop
bcf

Latch
Latch

■

receive status from pins at input latch

bcf
nop
bsf

Load
Load

Loop

Elf

Var,f

Rotate 'Var 1 one space to the left

btf ss
bcf
btf sc
bsf

Data
Var,0
Data
Var,0

■

Is Data line = '1 ' ?

If not, set erase bit '0' at Var variable

Is Dataline = ' 0' ?

If not set bit '0 '

bsf
nop
bcf

Clock
Clock

■

make one clock

decf sz
goto

Varl.f
L o op

■

are 8 bits received?
if not, repeat

en dm

Example of how to use the HC597 macro is given in the following program. Program receives data
from a parallel input of the shift register and moves it serially into the RX variable of the
microcontroller. LEDs connected to port B will indicate the result of the data input.

Program: HC597.INC

;***** Declaration and configuration of microcontroller *****

PROCESSOR 16f84
^include rr pl6f84. inc"

CONFIG _CP_0FF & _UDT_0FF & _PWRTE_0N & _XT_0SC

;***** Declaring the variables *****

Cblock 0x0 C ; beginning of RAH

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Chapter 6 - Samples

Cblock 0x0 C ; beginning

CountSPI

endc

of RAH

-*****

Declaring the hardware *****

#define Data PORTA,
#define Clock PORTA, 1
#define Latch PORTA, 2
#define Load PORTA, 3

■

can be any other 1/0 pin

-*****

Program memory structure

*****

ORG
goto

0x00
Main

■

reset vector

ORG
goto

0x04
Main

■

1»"

Interrupt vector

no interrupt routine

§ inc lude " b ank . inc "
§ include "he 5 9 7. inc"

■

assistant files

Main

BAHK1

movlw

mowf

clrf

BAHKO

b' 00010001'

TRISA

TRISB

■

■
■
■

beginning of a program

port A initialization
TRISA <- 0x11
Dins of nort B

clrf
bsf

PORTA
Load

■
■

PORTA <- 0x00

Enable SHIFT register

Loop

HCS97

movf

movwf

RX, CountSPI

RX,W

P0RTB

■

Status of input pins of SHIFT register
Are found in variable RX
Set the contents of RX register to
port B

goto
End

Loop

■
■

Repeat the loop
End of program

Output shift register

Output shift registers transform serial data into parallel data. On every rising edge of the clock,
the shift register reads the value from data line, stores it in temporary register, and then repeats
this cycle 8 times. On a signal from 'latch' line, data is copied from the shift register to input
register, thus data is transformed from serial into parallel data.

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Chapter 6 - Samples

input

Clock

Shift
register

Letch
register

1 Z

Qa -,

4-f

Qe
Qf

Qh -

An outline of the 74HC595 shift register connections is shown on the diagram below

i.lbF

330 £2 * .*. led i j

330.Q" M LID i

Connecting an output shift register to a microcontroller

Macro used in this example is found in hc595.inc file, and is called HC595
HC595mMacroVar,oVarl

variabplewhoser cotentsd istransferrled to outpuse of shift registe.

Chapter 6 - Samples

Example: HC595 Data, counter

The data we want to transfer is stored in data variable, and counter variable is used as a loop
counter.

Makro: HC595.INC

macro

Var,Varl

HC595

Local

Loop

■

local label

movlu

■
I*

transfer eight bits

movwf

Varl

■

counter initialisation

Loop

rlf

Var,f

■
r

Rotate 'Var' one space to the left

btf 33

STATUS ,

■

Is carry = ' 1 ' ?

bcf

Data

■

If not, set Data line to '0'

btf sc

STATUS ,

■

Is carry = ' ' ?

bsf

Data

■

If not, set Data line to '1'

bsf

Clock

Hake one clock

nop

bcf

Clock

decf sz

Varl,f

■

Are eight bits sent?

goto

Loop

■

If not, repeat

bsf

Latch

■

If all 8 bits have been sent, move the

nop

■

contents from SHIFT register to output latch

bcf

Latch

endm

An example of how to use the HC595 macro is given in the following program. Data from variable
TX is serially transferred to shift register. LEDs connected to the parallel output of the shift
register will indicate the state of the lines. In this example value OxCB (1100 1011) is sent so that
the eighth, seventh, fourth, second and first LEDs are illuminated.

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Chapter 6 - Samples

Program: HC595 . ASH

Microcontroller configuratic

******

m and declaration

*****

PROCESSOR 16f84

^include rr pl6f84.inc"

CONFIG _CP_0FF & _UDT_0FF

& _PTURTE_0N & _KT_0SC

- * ****

Declaring the variables *****

Cblock OxOC ;

Beginning of RAH

TX ;

Belongs to function "HC595"

CountSPI

endc

.*****

Declaring the hardware *****

tfdefine Data PORTA,

^define Clock PORTA, 1

tfdefine Latch PORTA, 2

.*****

Structure of program memory

*****

ORG 0x00 ;

Reset vector

goto Main

ORG 0x04 ;

Interrupt vector

goto Main ;

There is no interrupt routine

# i nc lud e "b ank . inc " ;

Assistant files

^include rr hc5 95. inc"

Main

■

BAHKl

Beginning of the program

movlu b' 00011000' ;

Port A initialization

mowf TRISA ;

TRISA <- 0x18

BAHK0

clrf PORTA ;

PORTA <- 0x00

movlu Oxcb ;

Fill the TX buffer

mowf TX ;

TX <- '11001011'

HC595 TX, CountSPI

Loop

goto Loop ;

Stay here

End ;

End of program

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Chapter 6 - Samples

page

Table of
contents

Chapter
overview

Next page ►

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Chapter 6 - Samples

page

Table of
contents

Chapter
overview

Next page ►

Seven-Segment Display (multiplexing)

The segments in a 7-segment display are arranged to form a single digit from to 9 as shown in
the animation:

We can display a multi-digit number by connecting additional displays. Even though LCD displays

are more comfortable to work with, 7-segment displays are still standard in the industry. This is

due to their temperature robustness, visibility and wide viewing angle. Segments are marked with

non-capital letters: a, b, c, d, e, f, g and dp, where dp is the decimal period.

The 8 LEDs inside each display can be arranged with a common cathode or common anode. With a

common cathode display, the common cathode must be connected to the Ov rail and the LEDs are

turned on with a logic one. Common anode displays must have the common anode connected to

the +5v rail. The segments are turned on with a logic zero.

The size of a display is measured in millimeters, the height of the digit itself (not the housing, but

the digit!). Displays are available with a digit height of 7,10, 13.5, 20, or 25 millimeters. They

come in different colors, including: red, orange, and green.

The simplest way to drive a display is via a display driver. These are available for up to 4

displays.

Alternatively displays can be driven by a microcontroller and if more than one display is required,

the method of driving them is called "multiplexing."

The main difference between the two methods is the number of "drive lines." A special driver may

need only a single "clock" line and the driver chip will access all the segments and increment the

display.

If a single display is to be driven from a microcontroller, 7 lines will be needed plus one for the

decimal point. For each additional display, only one extra line is needed.

To produce a 4, 5 or 6 digit display, all the 7-segment displays are connected in parallel.

The common line (the common-cathode line) is taken out separately and this line is taken low for

a short period of time to turn on the display.

Each display is turned on in turn and if this is repeated at a rate above 100 times per second, it

will appear that all the displays are on at the same time.

As each display is turned on, the appropriate information must be delivered to it so that it will give

the correct reading.

Up to 6 displays can be accessed like this without the brightness of each display being affected.

Each display is turned on very hard for one-sixth the time and the POV (persistence of vision) of

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Chapter 6 - Samples

our eye thinks the display is turned on the whole time.

All the timing signals for the display are produced by the program, the advantage of a

microcontroller driving the display is flexibility.

The display can be configured as an up-counter, down-counter, and can produce a number of

messages using letters of the alphabet that can be readily displayed.

The example below shows how to dive two displays.

+5v

O Sw1

[

— *

■a

\jT

RA2
RA3

RJWTOCKI
KICCR"

RA1

RAO

0SC1

0SC2

PIC
Vss 16F84 vdd

}

RBOJIMT
RBI
RB2
RB3

RB7
RB6
RB5
RB4

13-

4MH z

14 +

5vl

^-\l

33nn
■IZZI-

33DH

-l=K

33DH

i h

33nn
■IZZK

33nn
HZZh

33DH

■CZh

33DH

33DH
HZZK

f '0

o:-o

K c +

Q
J

■!

9
d

J +

Connecting a microcontroller to 7-segment displays in multiplex mode

File Led.inc contains two macros: LED_I nit and LED_Disp2. The first macro is used for display
initialization. That is where display refreshment period is defined as well as microcontroller pins
used for connecting the displays. The second macro is used for displaying numbers from to 99
on two displays.

Macro LED_Disp2 has one argument:

LED_Disp2 first macro

first is the number from to 99 to be displayed on Msd and Lsd digit.

Example: LED_Displ2 0x34

Number 34 will be shown on the display

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Chapter 6 - Samples

Realization of a macro is given in the following listing

■ ft ft ft ^ ft" MacrOS ft ft ft ft ft

LED Init

InitPorts
InitTimers

LED Disp2

macro

call

en dm

macro prvi

movlw prvi

movuf LO

call UpdateDisplay

en dm

;***** Subprograms *****

InitPorts

BANK1

clrf

LEDtrisA

ClEf

LEDtrisB

BAHKO

ClEf

LEDportA

ClEf

LEDportB

bsf

LEDportA,3

RETURN

InitTimers

BANK1

movlw

B'10000100

movwf

0PTI0N_REG

BANKO

movlw

B'00100000

movwf

IHTCON

movlw

.96

movwf

THRO

RET FIE

;***** Interrupt Routine *****

ISR

bcf

INTCON,GIE

btf sc

IHTCON,GIE

goto

ISR

movlw

.96

movwf

THRO

bcf

IHTCON, TOIF

call

Up d ateD i sp 1 ay

RETFIE

If aero: LED, INC

; Pins RAO -4 are output

; Port B is output

; Set all outputs to "0"

; /

; Turn on HSD display

; Hove the prescaler to THRO
; ps = 3 2

; Enable THRO interrupt

; Start the timer

; Disable all interrupts

; Check whether they are disabled

; Initialize the THRO

; Erase the int. (initialisation) flag

; "Refresh" the display

UpdateDisplay

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Chapter 6 - Samples

UpdateDi splay

movf LEDportA,U

clrf

andlw

movwf

bsf

rrf

btf 33

bcf
btf sc

LEDportA
0x0 f
TempC
TempC, 4
TempC, F
STATUS , C
TempC, 3
TempC,

goto UpdateHsd

UpdateLsd

call

ChkMsdZero

btf 33

STATUS , Z

movf

L0,Tff

andlw

0x0 f

goto

DisplayOut

UpdateHsd

swapf

L0,Tff

andlw

0x0 f

btf sc

STATUS , Z

movlw

0x0 a

DisplayOut

call

LedTable

mowf

LEDportB

movf

TempC, Iff

mowf

LEDportA

RETURJJ

LedTable

addwf

PCL, F

retlw

B'OOllllll'

retlw

B'00000110'

retlw

B'OlOllOll'

retlw

B'OlOOllll'

retlw

B'OllOOllO'

retlw

B'OllOllOl'

retlw

B'01111101 1

retlw

B'OOOOOlll'

retlw

B'Olllllll 1

retlw

B'OllOllll 1

retlw

B'00000000'

ChkMsdZero

movf

L0,lff

btfss

STATUS , Z

RETURJJ

retlw

-10

Display status -> w register

Turn off all 7-segment displays

Separate the lower half byte

Save display status in TempC

Beginning status of Lsd display

Set the status of the next display

c=l ?

If not, turn off the Lsd display

If it is, check the status of Hsd

display

If it is turned on, display the USD

digit of the number

; msd = ?

; If it is, skip

; Third Lsd digit -> w

Show it on the display

; Msd figure -> Iff

/
; msd != ?
; If it is, skip

Take the mask for a digit
Set the mask on port B
Turn on displays

; mask for

; no digit

digit

digit 1

digit 2

digit 3

digit 4

digit 5

digit 6

digit 7

digit 8

digit 9

Checking the leading zero

Msd figure -> Iff

= ? skip

If it is, skip

If not, go back from 10 to Iff reg

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Chapter 6 - Samples

xvjj i '-'.r-j.'j

f J_ J_ J. L, J-^J OJlJ-p

retlw -10

; If not, go back from 10 to XJ reg

The following example shows the use of macros in a program. Program displays number '21' in
two 7-segment digits.

Program: LED -ASH

;***** Declaring and configuring a microcontroller *****

PROCESSOR 16fS4

^include "pl6f84. inc"

CONFIG _CP_0FF & JJDTJJFF & _PWRTE_0N & _XTJ)SC

;***** Declaring the variables *****

Cblock 0x0 C

TempC

TempD

TempE

Count

endc

;***** Declaring the hardware *****

; Beginning of RAH

; Belongs to macro "LED Disp2"

LEDtrisA

equ

TRISA

LEDportA

equ

PORTA

LEDtrisB

equ

TRISB

LEDportB

equ

PORTB

;***** Program memory structure *****

Hain

ORG 0x0
goto Hain

ORG 0x0 4
goto ISR

^include "bank, inc"
^include "led- inc"

LED_Init

LED Disp2 0x21

loop goto

loop

; Reset vector

; Interrupt vector

; Interrupt routine is found

; in led. inc file

; Assistant file

; Beginning of the program

; Display on tuo 7-segment displays

; Number "21"

; Stay in the loop

End ; End of program

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Chapter 6 - Samples

End ; End of program

a Previous Table of Chapter wpyf nanp t

^ page contents overview M^y^ r

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Chapter 6 - Samples

Table of
contents

Chapter
overview

Next page ►

LCD Display

More microcontroller devices are using 'smart
LCD' displays to output visual information. The
following discussion covers the connection of a
Hitachi LCD display to a PIC microcontroller.
LCD displays designed around Hitachi's LCD
HD44780 module, are inexpensive, easy to use,
and it is even possible to produce a readout
using the 8 x 80 pixels of the display. Hitachi
LCD displays have a standard ASCII set of
characters plus Japanese, Greek and
mathematical symbols.

A 16x2 line Hitachi HD44780 display

Each of the 640 pixels of the display must be accessed individually and this is done with a number
of surface-mount driver/ controller chips mounted on the back of the display. This saves an
enormous amount of wiring and controlling so that only a few lines are required to access the
display to the outside world. We can communicate to the display via an 8-bit data bus or 4-bit
data bus.

For a 8-bit data bus, the display requires a +5v supply plus 11 I/O lines. For a 4-bit data bus it
only requires the supply lines plus seven extra lines. When the LCD display is not enabled, data
lines are tri-state which means they are in a state of high impedance (as though they are
disconnected) and this means they do not interfere with the operation of the microcontroller when
the display is not being addressed.

The LCD also requires 3 "control" lines from the microcontroller.

The Enable (E) line allows access to the display through R/W and RS lines. When this line is low,

the LCD is disabled and ignores signals from R/W and RS. When (E) line is high, the LCD checks

the state of the two control lines and responds accordingly.

The Read. Write (R/W) line determines the direction of data between the LCD and microcontroller.

When it is low, data is written to the LCD. When it is high, data is read from the LCD.

With the help of the Register select (RS) line, the LCD interprets the type of data on data lines.

When it is low, an instruction is being written to the LCD. When it is high, a character is being

written to the LCD.

Logic status on control lines:

E Access to LCD disabled
1 Access to LCD enabled

R/WO Writing data to LCD

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Chapter 6 - Samples

1 Reading data from LCD

RS Instruction
1 Character

Writing data to the LCD is done in several steps:

Set R/W bit to low

Set RS bit to logic or 1 (instruction or character)

Set data to data lines (if it is writing)

Set E line to high

Set E line to low

Read data from data lines (if it is reading)

Reading data from the LCD is done in the same way, but control line R/W has to be high. When we
send a high to the LCD, it will reset and wait for instructions. Typical instructions sent to LCD
display after a reset are: turning on a display, turning on a cursor and writing characters from left
to right.

When the LCD is initialized, it is ready to continue receiving data or instructions. If it receives a
character, it will write it on the display and move the cursor one space to the right. The Cursor
marks the next location where a character will be written. When we want to write a series of
characters, first we need to set up the starting address, and then send one character at a time.
Characters that can be shown on the display are stored in data display (DD) RAM. The size of
DDRAM is 80 bytes.

The LCD display also possesses 64 bytes of Character-
Generator (CG) RAM. This memory is used for characters
defined by the user. Data in CG RAM is represented as an 8-
bit character bit-map.

Each character takes up 8 bytes of CG RAM, so the total
number of characters, which the user can define is eight. In
order to read in the character bit-map to the LCD display, we
must first set the CG RAM address to starting point (usually
0), and then write data to the display. The definition of a
'special' character is given in the picture opposite.

CG RAM .

, , Bit map

address r

Data

0000

□ ■□■□

01010

0001

DDIDD

00100

0010

□ ■■■□

01110

0011

IDDDI

10001

0100

■ DDDD

10000

0101

IDDDI

10001

0110

□ ■■■□

01110

0111

DDDDD

00000

Before we access DD RAM after defining a special character, the program must set the DD RAM
address. Writing and reading data from any LCD memory is done from the last address which was
set up using set-address instruction. Once the address of DD RAM is set, a new written character
will be displayed at the appropriate place on the screen.

Until now we discussed the operation of writing and reading to an LCD as if it were an ordinary
memory. But this is not so. The LCD controller needs 40 to 120 microseconds (uS) for writing and
reading. Other operations can take up to 5 mS. During that time, the microcontroller can not
access the LCD, so a program needs to know when the LCD is busy. We can solve this in two
ways.

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Chapter 6 - Samples

Set DD RAM e

iddress

R/W

DB7

DB6

DBS

DB4

DB3

DB2

DB1

DBO

Set CG RAM address

R/W

DB7

DB6

DBS

DB4

DB3

DB2

DB1

DBO

Writ

e in i

data

to RAM

R/W

DB7

DB6

DBS

DB4

DB3

DB2

DB1

DBO

Re a

d dat

:a from RAM

R/W

DB7

DB6

DBS

DB4

DB3

DB2

DB1

DBO

A = address

D = data

One way is to check the BUSY bit found on data line D7. This is not the best method because
LCD's can get stuck, and program will then stay forever in a loop checking the BUSY bit. The other
way is to introduce a delay in the program. The delay has to be long enough for the LCD to finish
the operation in process. Instructions for writing to and reading from an LCD memory are shown
in the previous table.

At the beginning we mentioned that we needed 11 I/O lines to communicate with an LCD.
However, we can communicate with an LCD through a 4-bit data bus. Thus we can reduce the
total number of communication lines to seven. The wiring for connection via a 4-bit data bus is
shown in the diagram below. In this example we use an LCD display with 2x16 characters, labelled
LM16X212 by Japanese maker SHARP. The message 'character' is written in the first row: and two
special characters '—' and '}' are displayed. In the second row we have produced the word
'mikroElektronika'.

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Chapter 6 - Samples

+ 5v

[ F.u2

Rfcl
QRA3 RAO

0k [RMffOCKI QSC1

OSC2

[ MCLft

XJ"

PIC

[vss 16F84 ww

-- [Rl

[REM

-[ RB2

r{ RB3

Rft7

R-Ere

Rfr5
RM

4Mz

: —

Data
lines

R/IA"

Control lines

+5v

Connecting an LCD display to a microcontroller

File LCD.inc contains a group of macros for use when working with LCD displays.

tfakro: LCD. INC

;***** Declaring hardware *****
RS equ 1
RU equ 2

EN equ 3

;***** LCD commands *****

CONSTANT LCDEH8 = b 1 00110000'
CONSTANT LCDDZ = b' 100 00000'
CONSTANT LCDEH4 = b' 01000 00'

Signal Register Select

S i gnal Re ad/XJ r i te

Signal Enable Output / rr CLK"

; 8 -bit mode, 2 lines
; write to DDRAH
; 4-bit mode, 2 lines

; ***** Standard commands for LCD initialisation *** ( HI- / L0 -NIBBLE)

CONSTANT LCD2L = b' 001 01000'
CONSTANT LCDC0NT = b' 00001100'

CONSTANT LCDSH

= b' 00101000 '

function: 4 bit 2 lines
; Display control: Display ON,
Cursor OFF, blinking Cursor OFF
display mode: Auto Increment
; Cursor, NoDisplayAutoShift

;***** Standard LCD commands *****

;In order to send one of these commands to LCD, we need to use LCDcmd

. hZ .,,,._.._, 4_ .; nVm rt , r rr j rr. .-, t.-. .-3 T CT, nnrr

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Chapter 6 - Samples

;In order to send one of these commands to LCD, ue need to use LCDcmd
; function, ex. "LCDcmd LCDCLR"

clears display, resets the

cursor

cursor to the beginning

moving cursor to the right

moving cursor to the left

move the display contents to

the left

move the display contents to

the right

select the first line

select the second line

CONSTANT

LCDCLR

= b'

00000001 1

CONSTANT

LCDCH

= b

00000010 '

CONSTANT

LCDCR

= b

00000110 '

CONSTANT

LCDCL

= b

00000100 '

CONSTANT

LCDSL

= b

00011000 '

CONSTANT

LCDSR

= b

00011100 '

CONSTANT

LCDL1

= b

10000000 '

CONSTANT

LCDL2

= b

11000000 '

'^t^^t^i^r Macros ^^^^^

LCDinit

macro

call

LCD_init

en dm

LCDchar

macro

LCDarg

uuv.V ■
caiJ

LMdati

endm

LUDU

Diacso

caiJ

L^rdati

endm

LCDcmd

macro

LCD command

movlKT

LCD command

call

LCDcomd

endm

LCD line

macro

line num

LCD DDAdr

L CD initializ ation

write out the character on

LCD

send the command to LCD

IF (line_num == 1)
LCDcmd LCD LI

ELSE
IF (line_num == 2)
LCDcmd LCDL2

ELSE

EHDIF
END IF
endm

macro DDRamAddress

Local value = DDRamAddress

Start the macro with "First Line"
instruction

Start the macro with "Second Line"
instruction

b ' 1000 0000

; beginning of
; DDRAH

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Chapter 6 - Samples

Local value = DDRamAddress

b '10000000

; beginning of
; DDRAH

IF (DDRamAddress > 0x67)

ERROR "Wrong DDRAH address in LCD_DDAdr"
ELSE

movlu value

call LCDcomd
EHDIF
endm

LCD CGAdr

macro CGRamAddress

Local value = CGRamAddress

b '01000000

; Beginning of
; CGRAH-a

IF (CGRamAddress > b' 00111111')

ERROR "Wrong DDRAH address in LCD_CGAdr"
ELSE

movlu value

call LCDcomd
EHDIF
endm

;***** Subprograms *****

LCDcomd clrf LCDbuf
goto LCDur

LCDdata clrf LCDbuf

bsf LCDbuf, RS

LCDur

movuf

andlu

ioruf

movuf

call

clrf

suapf

LCDtemp

b' 11110000

LCDbuf,

LCDport

LCDclk
LCDport
LCDtemp,

; clear Data Flag

andlu b' 11110000'
ioruf LCDbuf,
movuf LCDport
call LCDclk
clrf LCDport
RETURH

LCDclk UAITX 0x01, 0x00

bsf LCDport, EN
bcf LCDport, EN
WAIT 0x01
RETURH

LCD_init

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; set Data Flag

Command / Data in Temp

set aside the upper half byte

set aside Data Flag

send the upper half byte to P0RTB

exchange the upper and louer half byte

places again

set aside the louer half byte

set aside the Data Flag

send the lou ha If byte to PORTE:

; Enable access to LCD for data and
; commands to be uritten in

Chapter 6 - Samples

LCD

init

clrf LCDport

BANK1

clrf 0PTI0N_RECt

movlT.j b ' 00000 000'

mowf LCDtris

prepare LCDport

BANKO
WAIT
movlu
mowf

r-o 1 1

0x01

LCDEH8

LCDport

t rrifliu

; START INITIALIZATION
; start with "8-bit mode"

4-bit mode

:sor

.to Inc , No Auto 5 hi f t

.ress counter to zero
defined by the user

characters
.ne is 8
0x00 ***

J! address

f:j it

toAl l"

movlu

mowf

call

clrf

movlu

mo^nuf

call

clrf

1.C]);kh v.

I ::l I

LCDDZ

LCDport

LCDclk

LCDport

LCDEH4

LCDport

LCDclk

LCDuort

write in DDRAH

go to 4 bit mode

LCDcmd LCD2L

LCDcmci LCDC0NT

LCDcmd LCDSH

LCDcmd LCDCLR

call LCDspecialChars

RETURN
LCDspecialChars

; function: 2 lines,

; display ON, no cur
; Mode displaying Au

; clear display, add
; read in characters
;to CGRAH

; maximum number of
; that user can defi

-** first special character is "E" at the position
*** is called from "LCDchar 0x00" ***

LCD_CGAdr 0x00
LCDchar b' 00001010'
LCD_CGAdr 0x01
LCDchar b' 00000100'
LCD_CGAdr 0x02
LCDchar b ' 00001110 '
LCD_CGAdr 0x03
LCDchar b' 00010 001'
LCD_CGAdr 0x04
LCDchar b' 00010000'
LCD_CGAdr 0x05
LCDchar b' 00010001'
LCD_CGAdr 0x06
LCDchar b' 00001110'
LCD_CGAdr 0x07

LCDchar b' 00000000'

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send CGRAH address
write data to CGRi

Chapter 6 - Samples

***

J-I address

LCD_CGAdr 0x07
LCDchar to' 00000000'

; *** second special character

is & at position 0x01

; *** is called

from "LCDchar

0x01" ***

LCD_CGAdr

0x08

; send CGRAH address

• LCDchar b

00000010'

; write data to CGRi

LCDchar b

00000100'

LCD_CGAdr

OxOA

LCDchar b

00001110'

L CD_C GAdr

Ox OB

LCDchar b

00010001'

LCD_CC-Adr

OxOC

LCDchar b

00010000'

LCD_CGAdr

OxOD

LCDchar b

00010001'

LCD_CGAdr

OxOE

LCDchar b

00001110'

LCD_CGAdr

Ox OF

LCDchar b

00000000'

LCD_DDAdr

0x00

; reset DDRAH

RETURN

Macro Terms

LCDinit macro used to initialize LCD. Initialize port for LCD. LCD is configured to work in four-bit

mode.

Example: LCDinit

LCDchar LCDarg Write ASCII character. Argument is ASCII sign.
Example: LCDChar 'd'

LCDw Write character found in W register.
Example: movlw 'p'
LCDw

LCDcmd LCDcommand Sending command instructions
Example: LCDcmd LCDCH

LCD_DDAdr DDRamAddress Set DD RAM address.
Example: LCD_DDAdr .3

LCDIine line_num Set cursor to the beginning of 1st or 2nd row
Example: LCDIine 2

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Chapter 6 - Samples

When working with a microcontroller the numbers are presented in a binary form.
As such, they cannot be displayed on a display. That's why it is necessary to change the numbers
from a binary system into a decimal system so they can be easily understood. Listings of two
macros LCDval_08 and LCDval_16 are given below. The first converts a number from the
binary system to the decimal system and displays it on an LCD display.

Macro LCDval_08 converts an eight-bit binary number into a decimal number from to 255 and
displays it on the LCD display. It is necessary to declare the following variables in the main
program: TEMPI, TEMP2, LO, LO_TEMP, Bcheck. An eight-bit binary number is found in variable
LO. When a macro is executed, the decimal equivalent of its number will be displayed on the LCD
display. The leading zeros before the number will not be displayed.

Hakro: LCDvOB. INC

■ ^^^^^ Hsn ros "fr^^^ft"

LCDval OS

macro

call LCDvalOS

endm

;***** Sub pcogr anas *****

LCDvalOS

movfu

movwf

L0_TEHP

ClEf

Bcheck

movlu

d'100'

movwf

TEHP2

call

VAL cnv

movlu

d'10'

movwf

TEHP2

call

VAL cnv

movlu

d'l '

movwf

TEHP2

bsf

Bcheck,

call

VAL cnv

RETURH

VAL cnv clef

TEMPI

movfu

TEHP2

VALcOl subuf

L0_TEMF,0

skpc

goto

LCDval2

incf

TEMPI, 1

rnovfu

TEMP2

subwf

L0_TEMP,1

bsf

Bcheck,

goto

VALcOl

LCDval2 movlu '0'
adduf TEMP 1,0
btfss Bcheck,
movlu ' ■

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Chapter 6 - Samples

btf 33

Bcheck,

movlu

i i

LCD u

RETURN

Macro LCDval_16 converts 16-bit binary number into decimal number from to 65535 and
displays it on LCD display. The following variables need to be declared in the main program:
TEMPI, TEMP2, TEMP3, LO, HI, LO_TEMP, HI_TEMP, Bcheck. A 16-bit binary number is found in
variables LO and HI. When a macro is executed, a decimal equivalent of this number will be
displayed on LCD display. The leading zeros before the number will not be displayed.

r l

Macro: LCDvl6. INC

UnJ -■*****

Macros *****
macro

LCDval_16

call LCDvallS

en dm

;***** Subpro

grams *****

LCDvall6

movfu

movuf

L0_TEMP

IHOVfU

mowf

HI_TEHP

clrf

Bcheck

movlu

b'00010000'

movuf

TEHP2

movlu

b'00100111 1

mowf

TEHP3

call

VALcnv

movlw

b'11101000 1

mOWf

TEHP2

movlu

b'00000011'

movuf

TEHP3

call

VALcnv

movlu

b'01100100'

mOWf

TEMP2

clrf

TEMP 3

call

VALcnv

movlu

b'OOOOlOlU 1

movuf

TEMP2

clrf

TEMP 3

call

VALcnv

movlu

b'00000001'

movwf

TEMP 2

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Chapter 6 - Samples

movlw

b'00000001'

movwf

TEMP 2

clrf

TEMP 3

bsf

Bcheck,0

call

VALcnv

RETURJJ

VALcnv clef

TEMPI

Vcnvl

movfir

TEMP 3

subwf

HI_TEHP ,

skpc

goto

L CDval 2

bnz

Vcnv2

movfw

TEMP 2

subwf

L0_TEMP,0

skpc

goto

L CDval 2

Vcnv2

movfw

TEMP 3

subwf

HI_TEHP , 1

movfw

TEMP 2

subwf

L0_TEMP,1

skpc

decf

HI TEMP,1

incf

TEMPI, 1

bsf

Bcheck,0

goto

Vcnvl

L CDval 2 movlw

■0'

addwf

TEMP 1 ,

btf ss

Bcheck,0

movlw

i i

LCDw

RETURN

The main program is a demonstration of how to use the LCD display and generate new characters
At the beginning of a program, we need to declare variables LCDbuf and LCDtemp used by
subprograms for the LCD as well as the microcontroller port connected to the LCD.
The program writes the message 'characters:' on the first row and shows two special characters
'—' and '}'. In the second row, 'mikroElektronika' is displayed.

- *****

PROCESSOR 16f84
^include rr pl6f84.inc"

CONFIG CP OFF & WDT OFF &

Program: LCD. ASM

PTOTE ON & >CT 03C

******

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Chapter 6 - Samples

- *****

Cblock OxOC

LCDbuf

LCDtemp

UCYCLE

PRESCuait

Po inter

endc

- *****

LCDtris equ TRISB
LCDport equ PORTB

-*****

ORG

0x00

goto

Main

ORG

0x04

goto

Main

Poruke

mowf

PCL

Porukal dt "

mlkRoEleKtrOnlkA"

Kraj

# i nc lud e "ft ank . inc "

# i nc lud e "uai t . inc "
^include "led. inc"
^include "print. inc

Main

LCDinit

LCD char

a '

LCD char

r '

LCD char

a '

LCD char

k ■

LCD char

t '

LCD char

e '

LCD char

r '

LCD char

i '

LCD char

. i

LCD char

LCD char 0x00
LCD char 0x01

LCD line 2

PRINT Poruke, Porukal, Kraj , Pointer, LCDw

http://www.mikroelektronika.co.yu/english/books/6_10Poglavlje.htm (12 of 13) [30/12/2001 16:54:44]

Chapter 6 - Samples

l llp line ^

Poruke,

Porukal,

Kraj,

Pointer,

LCDu

Loop

goto
End

Loop

a Previous Table of Chapter Npy1 - n - np k

^ page contents overview P^y c r

http://www.mikroelektronika.co.yu/english/books/6_10Poglavlje.htm (13 of 13) [30/12/2001 16:54:44]

Chapter 6 - Samples

page

Table of
contents

Chapter
overview

Next page ►

12-bit AD converter

Since everything in the microcontroller world is represented with "O's" and "l's", how do we cater
for a signal that is 0.5 or 0.77?

Most of the world outside a computer consists of audio signals. Apart from speech and music,
there are many quantities that need to be fed into a computer. Humidity, temperature, air
pressure, colour, turbidity, and methane levels, are just a few.

The answer is to take a number of digital lines and combine them so they can "read" an analogue
value. An analogue value is any value between and 1. You can also call it a "fractional value."
All the above quantities must now be converted to a value between and 1 so they can be fed
into a computer.

This is the broad concept. It becomes a little more complex in application.

If we take 8 lines and arrange than so they accept binary values, the total count will be 256 (this
is obtained by a count to 255 plus the value 0).

If we connect these 8 lines into a "black box," they will be called output lines and so we must
provide a single input line. With this arrangement we can detect up to 255 increments between
zero and "1." This black box is called a CONVERTER and since we are converting from Analogue
to Digital, the converter is called an A-to-D converter or AD CONVERTER.
AD converters can be classified according to different parameters. The most important
parameters are precision and mode of transferring data. As to precision, the range is: 8-bit,
10-bit, 12-bit, 14-bit, 16-bit. Since 12-bit conversion is an industrial standard, the example we
have provided below was done with a 12- bit AD converter. The other important parameter is the
way data is transferred to a microcontroller. It can be parallel or serial. Parallel transmission is
faster. However, these converters are usually more expensive. Serial transmission is slower, but i
terms of cost and fewer input lines to a microcontroller, it is the favourite for many applications.
Analogue signals can sometimes go above the allowed input limit of an AD converter. This may
damage the converter. To protect the input, two diodes are connected as shown in the diagram.
This will protect from voltages above 5v and below Ov.

In our example we used a LTC1286 12-bit AD converter (Linear Technology). The converter is
connected to the microcontroller via three lines: data, clock and CS (Chip Select). The CS line is
used to select an input device as it is possible to connect other input devices (eg: input shift
register, output shift register, serial AD converter) to the microcontroller and have them use the
same data lines.

The circuit below shows how to connect an AD converter, reference and LCD display to a micro.
The LCD display has been added to show the result of the AD conversion.

http://www.mikroelektronika.co.yu/english/books/6_11Poglavlje.htm (1 of 6) [30/12/2001 16:54:46]

Chapter 6 - Samples

Protection
diodes

+5v

Analogue inpul

+5v

*=■

flvref Hi

[ QHD

+5V

p-n ]

i -_- LTC1286

Vin=Itom ? to 40 V
o

rr?

VIp
TEWP

V-uTir

]
]

]

I---

i-n

+5v

1 0k

■a."

fcw^l/

-fl

* REF02

RAJ
RArtTQCKl

RA1

RAO

05C1

OSC2

PIC

Vst 16F84 Vdel

RHMNT
RBI

RBi
R&i

}

RET
RBti

RB5
R64[

1>:

}

4 +S-.

4MHz

IF-

Jfc-

■ 1

}

«■

+5V

+5v

Contrast

Connecting an AD converter with voltage reference to a microcontroller

The Macro used in this example is LTC86 and is found in LTC1286.inc file,

http://www.mikroelektronika.co.yu/english/books/6_11Poglavlje.htm (2 of 6) [30/12/2001 16:54:46]

Chapter 6 - Samples

Macro: LTC1286. INC

LTC86 macro Var LO, Var HI, Var

Loop

Loopl

CLK

Local

Loop

Local

Loopl

ClEf

Var LO

clrf

Var HI

movlw

mowf

Var

bcf

call

CLK

call

CLK

call

CLK

rlf

Var_RT,

btfss

Data

bcf

Var_RT,

btfsc

Data

bsf

Var_RT,

call

CLK

decfsz

Var,f

goto

Loop

movlw

mowf

Var

Elf

Var_L0,

btfss

Data

bcf

Var_L0,

btfsc

Data

bsf

Var_L0,

call

CLK

decfsz

Var,f

goto

Loopl

bsf

en dm

bsf

Clock

nop

bcf

Clock

RETUEH

The LTC86 Macro has three arguments:

LTC86 macro Var_LO, Var_HT, Var

Var_LO variable is where the result of lower byte conversion is stored

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Chapter 6 - Samples

Var_HI variable is where the result of higher byte conversion is stored
Var loop counter

Example: LTC86 LO, HI, Count

The four bits of the highest value are in variable HI , and first eight bits of conversion result are in
variable LO. Count is an assistant variable to count the passes through loops.

The following example shows how macros are used in the program. The program reads the value
from an AD converter and displays it on the LCD display. The result is given in quantum's. Eg: for
OV the result is 0, and for 5V it is 4095.

Program: LTC12S6. INC

PROCESSOR 16f84
^include rr pl6f84. inc"

CONFIG CP OFF & 1BDT OFF & PURTE ON & XT OSC

Cblock 0x0 C

LCDbuf

LCD temp

WCYCLE

PRE 5 C wait

TEH PI

TEHP2

TEHP3

L0_TEHP

HI_TEHP

Bcheck

Count

Pointer

endc

#define Data PORTA,
^define Clock PORTA, 1
#define CS PORTA, 2
LCDtris equ TRI5B
LCDport equ PORTB

ORG

0x00

goto

Ha in

ORG

0x04

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Chapter 6 - Samples

ORG
goto

iia j-ii

0x04
Main

Messages mowf PCL
Messaged dt "* LTC1286 * rr
Me ss age 1 dt "A/D rezul.:"
Kraj

^include

"bank. inc"
"ltcl286.inc"
"wait, inc"
"led. inc"

lcdvl6. inc"
print. inc"

Main

BAHK1
movlu
mowf
BAHKO

LOJTEMP

HI_TEMP

Bcheck

Count

Pointer

endc

Oxfl
TRI5A

.*****

#define Data PORTA,
^define Clock PORTA, 1
#define CS PORTA, 2
LCDtris equ TRISB
LCDport egu PORTB

ORG 0x00

go to Ma

ORG 0x04

go to Ma

Messages mowf

PCL

Messaged dt "*

LTC1286 *"

Message 1 dt "A/D rezul.:"

Kraj

^include

"bank. inc"

^include

"ltcl286. inc

^include

"wait, inc"

^include

"led. inc"

^include

"lcdvl6.inc"

^include

"print. inc"

http

Main

BAHK1

movlu Oxfl

■m n ttt.t-F TD T ^ A

//www.mikroelektronika.co.yu/english/books/6_1 1 Poglavlje.htm (5 of 6) [30/12/2001 16:54:46]

Chapter 6 - Samples

movlu Oxfl
mowf TRISA
BAHKO

LCDinit

clrf PORTA

LCD_DDAdE .3

PRIHT Messages, Messaged, Messagel, Pointer, LCDw

Loop LTC86 LO, HI, Count

call Out

goto Loop

Out

LCD line 2

PRIHT Messages, Messagel, EndMsg , Pointer, LCDw

LCDval_16

return

End

a Previous Table of Chapter Npy1 - n - n p k

" page contents overview M y "

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Chapter 6 - Samples

page

Table of
contents

Chapter
overview

Next page ►

Serial Communication

SCI is short for Serial Communication Interface and, as a special subsystem, it exists on most
microcontrollers. When it is not available, as is the case with PIC16F84, it can be created in
software.

Free line

I 1

data

As with hardware communication, we use standard NRZ (Non Return to Zero) format also known
as 8 (9)-N-l, or 8 or 9 data bits, without a pair bit and with one stop bit. Free line is defined as
the status of logic one. Start of transmission - Start Bit, has the status of logic zero. The data
bits follow the start bit (the first bit is the bit of the lowest value), and after the bits we place the
Stop Bit of logic one. The duration of the stop bit T depends on the speed of transmission and
is adjusted according to the needs of the transmission. For the transmission speed of 9600 baud,
Tisl04uS.

1 . CD (Carrier Detect)

2. RXD (Receive Data)

3. TXD (Transmit Data)

4. DTR (Data terminal Ready)

5. GND (Ground)

6. DSR (Data Set Ready)

7. RTS (Request To Send)

8. CTS (Clear To Send)

9. Rl (Ring Indicator)

Pin designations on RS232 connector

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Chapter 6 - Samples

In order to connect a microcontroller to a serial port on a PC computer, we need to adjust the
level of the signals so communicating can take place. The signal level on a PC is -10V for logic
zero, and +10V for logic one. Since the signal level on the microcontroller is +5V for logic one,
and OV for logic zero, we need an intermediary stage that will convert the levels. One chip
specially designed for the job is MAX232. This chip receives signals from -10 to +10V and converts
them into and 5V.
The circuit for this interface is shown in the diagram below:

SUB-D 9-pin
connector on
microcontroller
system

MAX232

Serial cable
(1 on 1)

Receives data (Rx)

Sends data (Tx)

Reset

+3-'

SUB-D 9-pin connector on PC

■OK

(

i
[

=" 9

[

T_/

RMTOCKI

MCLR

PIC
v 55 16FB4

RBOW

1
RB

2
RB

0SC1

0SC2

d
RB

7
RB

6
RB

5
RB

1-E-

14 +Sv

]

4MHz

■w-

-II-

Connecting a microcontroller to a PC via a MAX232 line interface chip.

File RS232.inc contains a group of macros used for serial communication.

- * *

■frtt*

Macro: RS232. INC

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Chapter 6 - Samples

Idefine RXport P0RTB,0
tfdefine RXtris TRISB.O

-**■***

CONSTANT LF
CONSTANT CR
CONSTANT TAB
CONSTANT BS

■ ft ft ^ ^ ft" M&CrOS ftftftftft

d 1 10'
d 1 13'
d'9'
d' 8'

RS232init macro

call

RS_init

en dm

SEND

macro

S_string

movlu

S_string

call

SENDsub

en dm

SENDu

macro

call

SENDsub

en dm

RECEIVE

macro

call

RECsub

en dm

Subprc

jgrams *****

RS_init bcf

Import

BANK1

clrf

0PTI0N_REG

bcf

TXtris

bsf

RXtris

BANKO

bsf

Import

movlu

b' 10010000'

mowf

INTCON

RETURN

SEND sub mowf TXD

bcf

TXport

movliT

0x0 8

mowf

RSJTEHP1

call

SJJait

SEND a

btf sc

TXD ,0

goto

SENDb

bcf

Import

goto

SENDc

SENDb

bsf

TXport

SENDc

rrf

TXD,!

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Chapter 6 - Samples

SENDb

bsf TXport

SENDc

rrf TXD,1

call 5_Uait

decfsz RS_TEMP1,1

goto SEND a

goto SENDd

SENDd

bsf Import

call 5_Uait

call 5 Wait

RETURN

S_Uait movlu Ox IE

movxjf RS_TEMP2

goto X_Uait

Rs_Uait movlw OxOC

mowf RS_TEMP2

goto X_Nait

R_Uait movlu OxlD

mowf RS_TEMP2

goto X_Uait

XJJait

decfsz RS_TEMP2,1

goto X_TJait

RETURN

RECsub

call Rs_Uait

btfsc RXport

goto REENTRY

movlKT 0x0 8

mowf RSJTEHP1

goto RECa

RECa

call R_Uait

btfss RXport

goto RECb

bsf RXD,0x07

goto RECc

RECb

bcf RXD,0x07

RECc

decfsz RS_TEMP1,0

rrf RXD,1

decfss RS_TEMP1,1

goto RECa

call R_Nait

btfss RXport

clrf RXD

RETURN

REEHTRY clrf RXD

goto IS Rend

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Chapter 6 - Samples

Using the macro:

RS232init Macro for initializing RBO pin and line for transmitting data (TX-pin).
Example: RS232init

SEND S_ string Sending ASCII character. Argument is ASCII sign.
Example: SEND g 1

SENDw Sending data found in W register.

Example: movlw 't'

SENDw

RECEIVE macro in interrupt routine receives data for RS232 and stores it in RXD register
Example:

ORG 0x04

goto ISR
ISR bcf INTCON,GIE

btfsc INTCON,GIE

goto ISR

RECEIVE

ISRend bcf INTCON, INTF
RETFIE

At the beginning of the main program, we need to declare variables RS_TEMP1, RE_TEMP2, TXD,
RXD and TX pin on microcontroller. After resetting a microcontroller the program sends a greeting
message to PC computer: $ PI V16F84 on line $, and is ready to receive data from RX line.
We can send and receive data from PC computer from some communication program. When
microcontroller receives data, it will send a message: Primljen karakter od PIC16F84: x (Character
received from PIC16F84: x), thus confirming that reception was successful.

Main program:

- *****

Program:

RS232.ASH

PROCESSOR 16f84

^include rr pl6f84.inc rr

CONFIG _CP_0FF & _¥DT_0FF &

_PWRTE_0N &

_XT_0SC

Cblock OxOC

RS TEMPI

D«! TTTWTJ?

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Chapter 6 - Samples

RSJTEHP1
RSJTEMP2

TXD
RXD

Pointer
endc

Messages mowf PCL

HessageO dt "Received character from PIC16F84"

Hessagel dt "$ PIC16F84 connected $"

Kraj

# i nc lud e "b ank . inc "
^include "rs232. inc"
^include "print. inc"

- *****

ISR bcf INTCON,GIE
btf sc INTCON, GIE
goto ISR

RECEIVE
SEND TAB

PRINT Messages, HessageO, Hessagel, Pointer, SENDw

movfw RXD
SENDw

SEND CR
SEND LF
SEND LF

ISRendbcf INTCON,INTF
RET FIE

Hain

RS232init

PRINT Hessages, Hessagel, EndHsg , Pointer, SENDw

SEND CR

SEND LF

SEND L F

Loop goto Loop
End

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Chapter 6 - Samples

a Previous Table of Chapter NpYt n - np t

™ page contents overview P^y c r

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Appendix A - Instruction Set

Table of
contents

Chapter
overview

Next page ►

Appendix A

I nstruction Set

I ntroduction

Appendix contains all instructions presented separately with examples for their use. Syntax,
description and its effects on status bits are given for each instruction.

A.l MOVLW
A. 2 MOVWF
A. 3 MOVF
A. 4 CLRW
A.5 CLRF
A. 6 SWAPF
A. 7 ADDLW
A.8 ADDWF
A.9 SUBLW
A.10 SUBWF
A. 11 ANDLW
A. 12 ANDWF
A. 13 IORLW
A. 14 IORWF
A. 15 XORLW
A. 16 XORWF
A.17 INCF
A. 18 DECF
A.19 RLF
A.20 RRF
A.21 COMF
A.22 BCF
A.23 BSF
A.24 BTFSC

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Appendix A - Instruction Set

q A.25 BTFSS

q A.26 INCFSZ

q A.27 DECFSZ

q A. 28 GOTO

q A. 29 CALL

q A.30 RETURN

q A. 31 RETLW

q A. 32 RETFIE

q A.33 NOP

q A. 34 CLRWDT

q A.35 SLEEP

A.l Write constant in W register

Syntax: [label] MOVLW k

Description: 8-bit constant k is written in W register

Operation: k => (W)

Operand: < k< 255

Flag:

Number of words: 1

Number of cycles: 1

Example 1 MOVLW 0X5A

After instruction: W=0x5A

Example 2 MOVLW REGISTAR

Before instruction: W=0xi0 and REGISTAR=0x40
After instruction: W=0x40

A. 2 Copy W to f

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Appendix A - Instruction Set

Syntax: [label] MOVWF f

Description: Contents of W register is copied to f register

Operation: W => (f )

Operand: < f < 127

Flag:

Number of words: 1

Number of cycles: 1

Example 1 MOVWF OPTION_REG

Before instruction: OPTION_REG = 0x20

W=0X40
After instruction: OPTION_REG = 0x40

W=0X40

Example 2 MOVWF INDF

Before instruction: W=Qxi7

FSR=0xC2

address contents 0xC2=0x00
After instruction: W=0xi7

FSR=0XC2

address contents 0xC2=0xi7

A. 3 Copy f to d

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Appendix A - Instruction Set

Syntax: [label] MOVF f, d

Description: Contents off register is stored in location determined by d operand

If d = J destination is W register,

If d = l, destination is f register itself,

Option d = l is used for testing the contents off register because

execution of this instruction affects Z flag in STATUS register.

Operation: f => (d)

Operand: < f < 127

d <= [0,1]
Flag: Z

Number of words: 1
Number of cycles: 1

Example 1 MOVF FSR,

Before instruction: FSR=0xC2

W=0X00

After instruction: W=0xC2

Z=0

Example 2 MOVF INDF,

Before instruction: W=0xi7

FSR=0XC2

address contents 0xC2=0x00
After instruction: W=0xi7

FSR=0XC2

address contents 0xC2=0x00

Z = l

A.4 Write in W

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Appendix A - Instruction Set

Syntax: [label] CLRW

Description: Contents of W register evens out to zero, and Z flag in STATUS

Operation: => (W)
Operand:

Flag: Z

Number of words: 1

Number of cycles: 1

Example CLRW

Before instruction: W=0x55
After instruction: W=0x00

Z = l

A.5 Write in f

Syntax: [label] CRLF f

Description: Contents off register evens out to zero, and Z flag in status

Operation: => f

Operand: < f < 127

Flag: Z

Number of words: 1
Number of cycles: 1

Example 1 CRLF STATUS

Before instruction: STATUS=0xC2
After instruction: STATUS=0x00

Z = l

Example 2 CLRF INDF

Before instruction: FSR=0xC2

address contents 0xC2=0x33
After instruction: FSR=0xC2

address contents 0xC2=0xnrj

Z = l

A.6 Copy the nibbles from f to d crosswise

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Appendix A - Instruction Set

Syntax: [label] SWAPF f, d

Description: Upper and lower half off register exchange places.

If d = 0, result is stored in W register.

If d = l, result is stored in f register.

Operation: f<0: 3> => d<4:7>, f<4:7> => d<0:3>;

Operand: < f < 127

d € [0,1]
Flag:

Number of words: 1

Number of cycles: 1

Example 1 SWAP REG,

Before instruction: REG = 0xF3
After instruction: REG = 0xF3

W=0X3F

Example 2 SWAP REG, 1

Before instruction: REG = 0xF3
After instruction: REG = 0x3F

A. 7 Add W to a constant

Syntax: [label] ADDLW k

Description: Contents of W register is added to 8-bit constant k and result is

stored in W register.

Operation: (W) + k => W

Operand: < k < 255

Flag: C, DC, Z

Number of words: 1

Number of cycles: 1

Example 1 ADDLW Ox IE

Before instruction: W=Oxio
After instruction: W=0x25

Example 2 ADDLW REG

Before instruction: W=0xi0

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Appendix A - Instruction Set

A.8 Add Wtof

Syntax: [label] ADDWF f, d

Description: Add contents of register W to register f

If d = 0, result is stored in W register.

If d = l, result is stored in f register.
Operation: (W) + (f ) => d

d e [0,1]
Operand: < f < 127

Flag: C, DC, Z

Number of words: 1
Number of cycles: 1

Example 1 ADDWF FSR,

Before instruction: W=0xi7

FSR=0XC2
After instruction: W=0xD9

FSR=0XC2

Example 2 ADDLW INDF, 1

Before instruction: W=0xi7

FSR=0XC0

address contents 0x02=0x20
After instruction: W=0xl7

FSR=0XC2

address contents 0xC2=0x37

A.9 Subtract W from a constant

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Appendix A - Instruction Set

Syntax: [label] SUBLW k

Description: Contents of W register is subtracted from k constant, and result is

stored in W register.

Operation: k - (W) => W

Operand: < k < 255

Flag: C, DC, Z

Number of words: 1

Number of cycles: 1

Example 1 SUBLW 0x03

Before instruction: W=0x0l, C = x, Z = x

After instruction: W=0x02 J C = lj Z=0 Result >

Before instruction: W=0x03 J C = x, Z = x

After instruction: W=0x00 J C = lj Z=l Result =

Before instruction: W=0x04 J C = x, Z = x

After instruction: W=0xFF J C=0, Z=0 Result <

Example 2 SUBLW REG

Before instruction: W=0xi0

contents REG = 0x37
After instruction: W=0x27

C = l Result >

A. 10 Subtract W from f

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Appendix A - Instruction Set

Syntax: [label] SUBWF f, d

Description: Contents of W register is subtracted from the contents off register

If d = 0, result is stored in W register.

If d = l, result is stored in f register,
Operation: (f) - (W) => d

Operand: < f < 127

d € [0,1]
Flag: C, DC, Z

Number of words: 1
Number of cycles: 1

Example 1 SUBWF REG, 1

Before instruction: REG = 3, W = 2, C = x, Z=x

After instruction: REG=1, W = 2, C = l, Z=0 Result >

Before instruction: REG = 2, W = 2, C = x, Z=x

After instruction: REG = J W = 2, C = l, Z = l Result =

Before instruction: REG=1, W = 2, C = x, Z=x

After instuction: REG = 0xFF J W=2, C = 0, Z=0 Result <

A. 11 Logic AND W with constant

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Appendix A - Instruction Set

Syntax: [label] ANDLW k

Description: Performs operation logic AND over the contents of W register and

constant k.

Result is stored in W register,
Operation: (W) .AND. k => W

Operand: < k < 255

Flag: Z

Number of words: 1
Number of cycles: 1

Example 1 ANDLW OxSF

Before instruction: W=0xA3 ; 0101 1111 (OxSF)

After instruction: W=0x03 ; 1010 0011 (0XA3)

; 0000 0011 (0X03)

Example 2 ANDLW REG

Before instruction: W=0xA3 ; 1010 0011 (0XA3)

REG = 0X37 ; 0011 0111 (0X37)
After instruction: W=0x23

; 0010 0011 (0X23)

A. 12 Logic AND W with f

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Appendix A - Instruction Set

Syntax: [label] ANDWF f, d

Description: Performs operation of logic AND over the contents of W and f

registers.

If d = 0, result is stored in W register,

If d = l, result is stored in f register.
Operation: (W).AND.f=>d

Operand: < f < 127

d € [0,1]
Flag: Z

Number of words: 1
Number of cycles: 1

Example 1 ANDWF FSR, 1

Before instruction: W=0xi7 J FSR=0xC2 ; 0001 0111 (0x17)

After instruction: W=0xi7 J FSR=02 ; 1100 0010 (0XC2)

Example 2 ANDWF FSR,

A. 13 Logic OR W with constant

; 0000 0010 (0X02)

Before instruction: W=0xi7, FSR=0xC2 ; 0001 0111 (0x17)

After instruction: W=0x02 J FSR=0xC2 ; 1100 0010 (0xC2)

; 0000 0010 (0X02)

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Appendix A - Instruction Set

Syntax: [label] IORLW k

Description: Operation logic OR is performed over the contents of W register and

over 8-bit constant k, and result is stored in W register.

Operation: (W) .OR. (k) => W

Operand: < k < 255

Flag: Z

Number of words: 1

Number of cycles: 1

Example 1 IORLW 0x35

Before instruction: W=0x9A
After instruction: W=0XBF

Z=0

Example 2 IORLW REG

Before instruction: W=0x9A

contenst REG = 0X37
After instruction: W=0x9F

Z=0

A. 14 Logic I LI W with f

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Appendix A - Instruction Set

Syntax: [label] IORWF f, d

Description: Operation logic OR is performed over the contents of W and f

registers,

If d = 0, result is stored in W register.

If d=l, result is stored in f register.
Operation: (W) OR. (f) => d

Operand: < f < 127

d € [0,1]
Flag: Z

Number of words: 1
Number of cycles: 1

Example 1 IORWF REG,

Before instruction: REG = 0xi3 J W=0x9l
After instruction: REG = 0xi3 J W=0x93

Z=0

Example 2 IORWF REG, 1

Before instruction: REG = 0xl3, W=0x91
After instruction: REG = 0x93, W=0x91

Z=0

A. 15 Logic exclusive OR W with constant

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Appendix A - Instruction Set

Syntax: [label] XORLW k

Description: Operation exclusive OR (XOR) is done over the contents of W

Operation: (W) .XOR. k => W

Operand: < k< 255

Flag: Z

Number of words: 1

Number of cycles: 1

Example 1 XORLW OxAF

Before instruction: W=0xBS ; 1010 1111 (OxAF)

After instruction: W=0xiA ; 1011 0101 (OxBS)

; 0001 1010 (0X1A)

Example 2 XORLW REG

Before instruction: W=0XAF ; 1010 1111 (0XA3)

REG = 0X37 ; 0011 0111 (0X37)

Afterinstruction: W=0xi8

Z=0 ; 0001 1000 (0X18)

A. 16 Logic exclusive OR W with f

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Appendix A - Instruction Set

Syntax: [label] XORWF f, d

Description: Operation exclusive OR is performed over the contents of W and f

registers,

If d = 0, result is stored in W register,

If d = l, result is stored in f register.
Operation: (W) ,XOR. (f) => d

Operand: < f < 127

d € [0,1]
Flag: Z

Number of words: 1
Number of cycles: 1

Example 1 XORWF REG, 1

Before instruction: REG = 0xAF J W=0xBS ; 1010 1111 (OxAF)

After instruction: REG = 0xiA J W = 0xB5 ; 1011 0101 (OxBS)

A. 17 Increment f

; 0001 1010 (0X1A)

Example 2 XORWF REG,

Before instruction: REG = 0xAF, W=0xBE ; 1010 1111 (OxAF)

After instruction: REG = 0xAF J W=0xiA ; 1011 0101 (OxBS)

; 0001 1010 (0X1A)

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Appendix A - Instruction Set

Syntax: [label] INCF f, d

Description: Increments f register by one.

If d = Oj result is stored in W register
If d = lj result is stored in f register,

Operation: (f ) + 1 => d

Operand: < f < 127

d <= [0,1]
Flag: Z

Number of words: 1
Number of cycles: 1

Example 1 INCF REG, 1

Before instruction: REG = 0xFF

Z=0
After instruction: REG = 0x00

Z = l

Example 2 INCF REG,

Before instruction: REG = 0xi0

W = x

Z=0
After instruction: REG = 0xl0

W=0X11

Z=0

A. 18 Decrement f

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Appendix A - Instruction Set

Syntax: [label] DECF f, d

Description: Decrements f register by one.

If d = Oj result is stored in W register
If d = lj result is stored in f register.

Operation: (f ) - 1 => d

Operand: < f < 127

d € [0,1]
Flag: Z

Number of words: 1
Number of cycles: 1

Example 1 DECF REG, 1

Before instruction: REG = 0x01

Z=0
After instruction: REG = 0x00

Z = l

Example 2 DECF REG,

Before instruction: REG = 0xi3

W = x

Z=0
After instruction: REG = 0xl3

W=0X12
Z=0

A. 19 Rotate f to the left through CARRY

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Appendix A - Instruction Set

Syntax:
Description:

Operation:
Operand:

Flag:

Number of words

Number of cycles

[label] RLF f, d

Contents off register is rotated by one space to the left through C

(Carry) flag,

If d = J result is stored in W register,

If d = lj result is stored in f register.

(f<n>) => d<n + l>, f<7> => C, C => d<0>;

< f < 127

d € [0,1]

c
1
1

Example 1 RLF REG,

Before instruction: REG=1110 0110

C=0
After instruction: REG=1110 0110

W = 1100 1100

C = l

Example 2 RLF REG, 1

Before instruction: REG=1110 0110

C=0
After instruction: REG=1100 1100

C = l

ril

re gi star f

■*

~ 1

A.20 Rotate f to the right through CARRY

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Appendix A - Instruction Set

Syntax:
Description:

Operation:
Operand:

Flag:

Number of words

Number of cycles

[label] RRF f, d

Contents of f register is rotated by one space to the right through C

(Carry) flag.

If d = 0, result is stored in W register.

If d = l, result is stored in f register.

(f<n>) => d<n-l>, f<0> => C, C => d<7>;

< f < 127

d € [0,1]
C

registarf

Example 1 RRF REG,

Before instruction: REG=1110 0110

W = x

C=0
After instruction: REG=1110 0110

W=0111 0011
C=0

Example 2 RRF REG, 1

Before instruction: REG=1110 0110

C=0
After instruction: REG = 0111 0011

C=0

A.21 Complement f

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Appendix A - Instruction Set

Syntax:
Description:

Operation:
Operand:

Flag:

Number of words: 1

Number of cycles: 1

Example 1 COMF REG,

Before instruction: REG = 0xi3

After instruction: REG = 0xl3

W=0XEC

[label] COMF f, d

Contents off register is complemented
If d = 0, result is stored in W register.
If d = l, result is stored in f register.

< f < 127
d <= [0,1]

; 0001 0011 (0X13)
; complement

; 1110 1100 (0XEC)

Example 2 COMF INDF, 1

Before instruction: FSR=0xC2

address contents (FSR)=0xAA
After instruction: FSR=0xC2

address contents (FSR)=0x55

A. 22 Reset bit b in f

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Appendix A - Instruction Set

Syntax: [label] BCF f, b

Description: Reset bit b in f register.

Operation: (0)^f<b>

Operand: < f < 127

< b < 7
Flag:

Number of words: 1

Number of cycles: 1

Example 1 BCF REG, 7

Before instruction: REG = 0xC7 ; 1100 0111 (0XC7)

After instruction: REG = 0x47 ; 0100 0111 (0x47)

Example 2 BCF INDF, 3

Before instruction: W=0xi7

FSR=0XC2

address contents (FSR)=0x2F
After instruction: W=0xi7

FSR=0XC2

address contents (FSR)=0x27

A.23 Set bit b in f

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Appendix A - Instruction Set

Syntax: [label] BSF f, b

Description: Set bit b in f register.

Operation: l=>f<b>

Operand: < f < 127

< b < 7
Flag:

Number of words: 1

Number of cycles: 1

Example 1 BSF REG, 7

Before instruction: REG = 0X07 ; 0000 0111 (0x07)

After instruction: REG = 0xi7 ; 1000 0111 (0x17)

Example 2 BCF INDF, 3

Before instruction: W=0xi7

FSR=0xC2

address contents (FSR)=0x20
After instruction: W=0xi7

FSR=0XC2

address contents (FSR)=0x28

A. 24 Test bit b in f, skip if it =

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Appendix A - Instruction Set

Syntax: [label] BTFSC f, b

Description: If bit b in f register equals zero, then we skip the next instruction.

If bit b equals zero, during execution of the current instruction,
execution of the next one is disabled, and NOP instruction executes
instead thus making the current one a two-cycle instruction.

Operation: Skip next instruction if (f<b>) =

Operand: < f < 127

< b < 7

Flag:

Number of words: 1

Number of cycles: 1 or 2 depending on a b bit

Example

LAB_01 BTFSC REG,1 ;Test bit no.l in REG

LAB_02 j Skip this line if =0

LAB_03 j Skip here if =1

Before instruction, program counter was at address LABJDl.

After instruction, if the first bit in REG register was zero, program counter points to
address LABJD3.

If the first bit in REG register was one, program counter points to address LAB_02.

A.25 Test bit b in f, skip if =1

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Appendix A - Instruction Set

Syntax: [label] BTFSS f, b

Description: If bit b in f register equals one, then skip over the next instruction

If bit b equals one, during execution of the current instruction, the
next one is disabled, and NOP instruction is executed instead, thus
making the current one a two-cycle instruction.

Operation: Skip next instruction if (f<b>) = l

Operand: < f < 127

< b < 7

Flag:

Number of words: 1

Number of cycles: 1 or 2 depending on a b bitj

Example

LAB_01 BTFSS REG,1 ;Test bit no.l in REG

LAB_02 j Skip this line if = 1

LAB_03 j Skip here if =0

Before instruction, program counter was at address LAB_01

After instruction, if the first bit in REG register was one, program counter points to
address LABJD3.

If the first bit in REG register was zero, program counter points to address LAB_02.

A.26 Increments skip if=0

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Appendix A - Instruction Set

Syntax:
Description:

[label] INCFSZ f, d

Contents off register is incremented by one.

If d = 0, result is stored in W register.

If d = l, result is stored in f register.

If result =0, the next instruction is executed as NOP making the

current one a two-cycle instruction.

(f ) + 1 => d

< f < 127

d € [0,1]

Operation:
Operand:

Flag:

Number of words: 1

Number of cycles: 1 or 2 depending on a result

Example

LAB_01
LAB_02
LAB 03

INCFSZ REG, 1

; Increase the contents REG by one
; Skip this line if =0
; Skip here if =0

The contents of program counter before instruction, PC=address LAB_01

The contents of REG register after executing an instruction REG = REG + 1 J if REG = 0,
program counter points to label address LAB_03. Otherwise, program counter points to
address of the next instruction or to LAB 02.

A.27 Decrement f, skip if =

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Appendix A - Instruction Set

Syntax:
Description:

[label] DECFSZ f, d

Contents off register is decremented by one.

If €1 = 0, result is stored in W register.

If d = lj result is stored in f register.

If result = 0, next instruction is executed as NOP, thus making the

current one, a two-cycle instruction.

(f ) - 1 => d

< f < 127

d € [0,1]

Operation:
Operand:

Flag:

Number of words: 1

Number of cycles: 1 or 2 depending on a result

Example

LAB_01
LAB_02
LAB 03

DECFSZ CNT, 1

; Decrement the contents REG by one
; Skip this line if =
; Skip here if = 1

The contents of program counter before instruction, PC=address LAB_01

The contents of CNT register after executing an instruction CNT=CNT-1, if CNT=0,
program counter points to address of label LAB_03. Otherwise, program counter points to
address of the following instruction, or to LABJD2.

A.28 J ump to address

Syntax:

Description:

Operation:

Operand:

Flag:

Number of words: 1

Number of cycles: 2

Example

[label] GOTO k

Unconditional jump to address k.
k=>PC<10:0>, (PCLATH<4:3>)
< k < 2048

PC<12:11>

LAB 00

GOTO LAB 01

; Jump to LAB_01

LAB_01

Before instruction: PC=address LAB_00
After instruction: PC=address LAB 01

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Appendix A - Instruction Set

A.29 Call a program

Syntax:
Description:

Operation:

[label] CALL k

Instruction calls a subprogram. First; return address (PC+1) is

stored on stack, then 11-bit direct operand k, which contains the

subprogram address, is stored in program counter.

(PC) + 1 => Top Of Stack (TOS)

k=> PC<10:0> J (PCLATH<4:3>) => PC<12:11>

Operand:

Flag:

Number of words: 1

Number of cycles: 2

Example

< k< 2048

LAB 01

CALL LAB 02

; Call subrutine LABJD2

LAB_02

Before instruction: PC=address LABJD1

TOS=x

After instruction: PC=address LABJD2

TOS=LAB_01

A.30 Return from a subprogram

Syntax:

Description:

Operation:

Operand:

Flag:

Number of words: 1

Number of cycles: 2

[label] RETURN

Contents from the top of a stack is stored in program counter

TOS => program counter PC

Example

RETURN

Before instruction: PC = x

TOS=x

After instruction: PC=TOS

TOS=TOS-l

A.31 Return from a subprogram with constant in W

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Appendix A - Instruction Set

Syntax: [label] RETLW k

Description: 8-bit constant k is stored in W register. Value off the top of a stack

is stored in program counter.

Operation: (k) => W; TOS => PC

Operand: < k < 255
Flag:

Number of words: 1

Number of cycles: 2

Example RETLW 0x43

Before instruction: W = x

PC = x

TOS=x

After instruction: W=0x43

PC=TOS

TOS=TOS-l

A.32 Return from interrupt routine

Syntax: [label] RETFIE

Description: Return from a subprogram. Value from TOS is stored in program

counter PC. Interrupts are enabled by setting a GIE (Global

interrupt Enable) bit.
Operation: TOS => PC; 1 => GIE

Operand:
Flag:

Number of words: 1
Number of cycles: 2

Example RETFIE

Before instruction: PC = x

GIE =
After instruction: PC=TOS

A.33 No operation

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Appendix A - Instruction Set

Syntax: [label] NOP

Description: Does not execute any operation or affect any flag.

Operation:

Operand:

Flag:

Number of words: 1

Number of cycles: 1

Example NOP

Before instruction: PC = x
After instruction: PC = x + i

A.34 Initialize watchdog timer

Syntax: [label] CLRWDT

Description: Watchdog timer is reset. Pre scaler of the Watchdog timer is also

reset, and status bits TO and PD are set also.
Operation: => WDT

=> WDT prescaler

1 =>TO
1 => PD

Operand: -_

Flag: TO, PD

Number of words: 1

Number of cycles: 1

Example CLRWDT

Before instruction: WDT counter=x

WDT prescaler=l: 128
After instruction: WDT counter=0x00

WDT prescaler counter=0

TQ=1

PD=1

WDT prescaler=l: 128

A.35 Stand by mode

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Appendix A - Instruction Set

Syntax: [label] SLEEP

Description: Processor goes into low consumption mode. Oscillator is stopped.

PD (Power Down) status bit is reset. To (Timer Out) bit is set. WDT

(Watchdog) timer and its prescaler are reset.
Operation: => WDT

=> WDT prescaler

1 =>TO

=> PD

Operand: -

Flag: TO, PD

Number of words: 1
Number of cycles: 1

Example SLEEP

Before instruction: WDT counter=x

WDT prescaler=x

After instruction: WDT counter=0x00

WDT prescaler=0
TO=l
PD =

a Previous Table of Chapter wpyf nanp t

^ page contents overview M^y^ r

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Appendix B - Numeric Systems

Decimal numeric system is defined by its basis 10 and decimal space that is counted from right to
left, and consists of numbers 1, 2, 3, 4, 5, 6, 7, 8, 9. That means that the end left number of the
total sum is multiplied by 1, next one by 10, next by 100, etc.

Example:

4631

1*10°
3*10 1
6*10 2
4* 10 3

600

4000

Result = 4631

Operations of addition, subtraction, division, and multiplication in a decimal numeric system are
used in a way that is already known to us, so we won't discuss it further.

B.2 Binary numeric system

Binary numeric system differs in many aspects from the decimal system we are used to in our
everyday lives. Its numeric basis is 2, and each number can have only two values, T or '0'.
Binary numeric system is used in computers and microcontrollers because it is far more suitable
for processing than a decimal system. Usually, binary number consists of binary numbers 8, 16 or
32, and it is not important in view of the contents of our book to discuss why. It will be enough for
now to adopt this information.

Example:

10011011 binary number with 8 digits

In order to understand the logic of binary numbers, we will consider an example. Let's say that we
have a small chest with four drawers, and that we need to tell someone to bring something from
one of the drawers to us. Nothing is more simple, we will say left side, bottom (drawer), and the
desired drawer is clearly defined. However, if we had to do this without the use of instructions like
left, right, beneath, above, etc., then we would have a problem. There are many solution to this
problem, but we should look for one that is most beneficent and practical! Lets designate rows
with A, and types with B. If A=l, it refers to the upper row of drawers, and for A=0, bottom row.
Similarly with columns, B=l represents the left column, and B=0, the right (next picture). Now it
is already easier to explain from which drawer we need something. We simply need to state one of
the four combinations: 00, 01, 10 or 11. This characteristic naming of each drawer individually is
nothing but binary numeric representation, or conversion of common numbers from a decimal into
binary form. In other words, references like "first, second, third and fourth" are exchanged with
"00,01, 10 and 11".

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Appendix B - Numeric Systems

A=0

A=1

B=0

B=1

DRAWERS 1
00

DRAWERS 2
01

DRAWERS 3
10

DRAWERS 4
11

What remains is for us to get acquainted with logic that is used with binary numeric system, or
how to get a numeric value from a series of zeros and ones in a way we can understand, of
course. This procedure is called conversion from a binary to a decimal number.

Example:

10011011

1*2° =

T2 1 =
0*2 2 =
1*2 3 =
1*2 4 =
0*2 5 =
0*2 6 =
1*2 7 =

128

Result = 155

As you can see, converting a binary number into a decimal number is done by calculating the
expression on the left side. Depending on the position in a binary number, digits carry different
values which are multiplied by themselves, and by adding them we get a decimal number we can
understand. Let's further suppose that there are few marbles in each of the drawers: 2 in the first
one, 4 in the second drawer, 7 in the third and 3 in the fourth drawer. Let's also say to the one
who's opening the drawers to use binary representation in answer. Under these conditions,
question would be as follows: "How many marbles are there in 01?", and the answer would be:
"There are 100 marbles in 01." It should be noted that both question and the answer are very
clear even though we did not use the standard names. It should further be noted that for decimal
numbers from to 3 it is enough to have two binary digits, and that for all values above that we
must add new binary digits. So, for numbers from to 7 it is enough to have three digits, for
numbers from to 15, four, etc. Simply said, the biggest number that can be represented by a
binary digit is the one obtained when basis 2 is graded onto a number of binary digits in a binary
number and thus derived number is decremented by one.

Example:

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Appendix B - Numeric Systems

2 4 -1= 16-1= 15

This means that it is possible to represent decimal numbers from to 15 with 4 binary digits,
including numbers '0' and '15\ or 16 different values.

Operations which exist in decimal numeric system also exist in a binary system. For reasons of
clarity and legibility, we will review addition and subtraction only in this chapter.

Basic rules that apply to binary addition are:

10 1

+ +1 +0 +1

~T" ~T~ "0" TO"

Addition is done so that digits in the same numeric positions are added, similar to the decimal
numeric system. If both digits being added are zero, their sum remains zero, and if they are '0
and '1', result is '1'. The sum of two ones gives a zero, but with transferring '1' to a higher
position that is added to digits from that position.

Example:

1010 First number
1001 Second number

10011 Result

We can check whether result is correct by transferring these number to decimal numeric system
and by performing addition in it. With a transfer we get a value 10 as the first number, value 9 as
the second, and value 19 as the sum. Thus we have proven that operation was done correctly.
Trouble comes when sum is greater than what can be represented by a binary number with a
given number of binary digits. Different solutions can be applied then, one of which is expanding
the number of binary digits in the sum as in the previous example.

Subtraction, like addition is done on the same principle. The result of subtraction between two
zeros, or two ones remains a zero. When subtracting zero and one, we have to borrow one from
binary digit which has a higher value in the binary number.

Example:

1010 First number
1001 Second number

0001 Result

By checking the result as we did with addition, when we translate these binary numbers we get
decimal numbers 10 and 9. Their difference corresponds to number 1 which is what we get in

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Appendix B - Numeric Systems

subtraction.

B.3 Hexadecimal numeric system

Hexadecimal numeric system has a number 16 as its basis. Since the basis of a numeric system is
16, there are 16 different digits that can be found in a hexadecimal number. Those digits are "0,
1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F". Letters A, B, C, D, E and F are nothing but values 10, 11,
12, 13, 14 and 15. They are introduced as a replacement to make writing easier. As with a binary
system, here too, we can determine with same formula what is the biggest decimal number we
can represent with a specific number of hexadecimal digits.

Example:

16 2 -1= 256-1 = 255

Usually, hexadecimal number is written with a sign "$" or "Ox" before it, to emphasize the numeric
system. Thus, number A37E would be written more correctly as $A37E or 0xA37E. In order to
translate a hexadecimal number into a binary numeric system it is not necessary to perform any
calculation but simple exchange of hexadecimal digits with binary digits. Since the maximum value
of a hexadecimal number is 15, that means that it is enough to use 4 binary digits for one
hexadecimal digit.

Example:

SE4 = 1110 0100

By checking, or transferring both numbers into decimal numeric system, we get a number 228
which proves the accuracy of our action.

In order to get a decimal equivalent of a hexadecimal number, we need to multiply each digit of a
number with number 16 which is gradated by the position of that digit in hexadecimal number.

Example:

A37E

14*16°
7*16 1
3*16 2

1 0* 1 6 3

112

768

40960

Result = 41854

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Appendix B - Numeric Systems

Addition is, like in two preceding examples, performed in a similar manner.
Example:

J3A2B First number
+ $A9C1 Second number

$E3EC Result

We need to add corresponding digits of the number; and, if their sum is higher than 16, we need
to write number '0' there. The value above 16 should be added to the sum of the next two digits
higher in value. By checking, we get 14891 as the first number, and second is 43457. Their sum is
58348, which is a number $E3EC when it is transferred into a decimal numeric system.
Subtraction is an identical process to previous two numeric systems. If the number we are
subtracting from is smaller, we borrow from the next place of higher value.

Example:

J2D46 First number
+ $1752 Second number

J15F4 Result

By checking this result, we get values 11590 for the first number and 5970 for the second, where
their difference is 5620, which corresponds to a number $15F4 after a transfer into a decimal
numeric system.

Conclusion

Binary numeric system is still the one that is most in use, decimal the one that's easiest to
understand, and a hexadecimal is somewhere between those two systems. Its easy conversion to
a binary numeric system and easy memorization make it, along with binary and decimal systems,
one of the most important numeric systems.

a Previous Table of Chapter npy1- nanp t

™ page contents overview |>1CAL pciye w

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Appendix C - Glossary

a Previous Table of Chapter

^ page contents overview

Appendix C

Glossary

Introduction

q Microcontroller

q I/O pin

q Software

q Hardware

q Simulator

q ICE

q EPROM Emulator

q HEX file

q List file

q Source File

q Debugging

q ROM, EPROM, EEPROM, FLASH, RAM

q Addressing

q ASCII

q Carry

q Code

q Byte f Kilobyte, Megabyte

q Flag

q Interrupt vector or interrupts

q Programmer

q Product

I ntroduction

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Appendix C - Glossary

Since all the fields of man's activity are regularly based on adequate and already adopted terms
(through which other notions and definitions become), so in the field of microcontrollers we can
single out some frequently used terms. Ideas are often connected so that correct understanding of
one notion is needed in order to get acquainted with one or more of the other ideas.

Microcontroller

Microprocessor with peripherals in one electronic component.

I/O pin

External microcontroller's connector pin which can be configured as input or output. In most cases
I/O pin enables a microcontroller to communicate, control or read information.

Software

Information that microcontroller needs in order to be able to function. Software can not have any
errors if we want the program and a device to function properly. Software can be written in
different languages such as: Basic, C, pascal or assembler. Physically, that is a file on computer
disc.

Hardware

Microcontroller, memory, supply, signal circuits and all components connected with

microcontroller.

The other way of viewing this (especially if it's not working) is, that, hardware is something you

can kick.

Simulator

Software package for PC which simulates the internal function of microcontroller. It is ideal for
checking software routines and all the parts of the code which do not have over demanding
connections with an outside world. Options are installed to watch the code, movement around the
program back and forth step by step, and debugging.

ICE

ICE (In Circuit Emulator), internal emulator, very useful part of the equipment which connects a
PC instead of microcontroller on a device that is being developed. It enables software to function
on the PC computer, but to appear as if a real microcontroller exists in the device. ICE enables you
to move through program in real time, to see what is going on in the microcontroller and how it
communicates with an outside world.

EPROM Emulator

EPROM Emulator is a device which does not emulate the entire microcontroller like ICE emulator,
but it only emulates its memory. It is mostly used in microcontrollers that have external memory.
By using it we avoid constant erasing and writing of EPROM memory.
Assembler

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Appendix C - Glossary

Software package which translates source code into a code which microcontroller can understand.
It contains a section for discovering errors. This part is used when we debug a program from
errors made when program was written.

HEX file

This is a file made by assembler translator when translating a source file, and has a form
"understood" by microcontrollers. A continuation of the file is usually File_name.HEX where the
name HEX file comes from.

List file

This is a file made by assembler translator and it contains all instructions from source file with
addresses and comments programmer has written. This is a very useful file for keeping track of
errors in the program. File extension is LST which is where its name comes from.

Source File

File written in the language understood by man and assembler translator. By translating the
source file, we get HEX and LIST files.

Debugging

Error made in writing a program, which error we are not aware of. Errors can be quite simple such
as typing errors, and quite complex such as incorrect use of program language. Assembler will find
most of these errors and report them to '.LST' file. Other errors will need to be searched for by
trying it out and watching how device functions.

ROM, EPROM, EEPROM, FLASH, RAM

Types of memories we meet with microcontroller use. First one can not be erased, what you write
in it once, stays forever, and can not be erased. The second is erasable electrically with supply
brought in separately, and voltage above that on which microcontroller is operating. Third one can
also be erased electrically, but uses voltage which microcontroller operates on. Fourth one is
electrically erasable, but unlike EEPROM memory it does not have such a great number of cycles
of writing and erasing at memory locations. Fifth one is fast, but it does not hold back the
contents as the previous when there is supply shortage. Thus, program is not stored in it, but it
serves for different variables and inter-results.

Addressing

Determines and designates certain memory locations.

ASCII

Short for "American Standard Code for Information Interchange". It is widely accepted type of
coding where each number and letter have their eight-bit code.

Carry

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Appendix C - Glossary

Transfer bit connected with arithmetic operations

Code

File, or section of a file which contains program instructions.

Byte, Kilobyte, Megabyte

Terms designating amounts of information. The basic unit is a byte, and it has 8 bits. Kilobyte has
1024 bytes, and mega byte has 1024 kilobytes.

Flag

Bits from a status register. By their activation, programmer is informed about certain actions.
Program activates its response if necessary.

Interrupt vector or interrupts

Location in microcontroller memory. Microcontroller takes from this location information about a
section of the program that is to be executed as an answer to some event of interest to
programmer and device.

Programmer

Device which makes it possible to write software in microcontroller memory, thus enabling the
microcontroller to work independently. It consists of the hardware section usually connected with
one of the ports and software section used on the computer as a program.

Product

Product development is a combination of luck and experience. Short terms, or time-limits for
production should be avoided because even with most simple assignments, much time is needed
to develop and improve. When creating a project, we need time, quiet, logical mind and most
importantly, a thorough understanding of consumer's needs. Typical course in creating a product
would have the following algorithm.

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Appendix C - Glossary

Request

Expenditures

JiL

Time lim

j=i

Ski

±L

)

Determining
a fee

jji

Outline ^
iL

Making the i
hardware part j

jiii

Making the
software part y

Jj=L

jj Making the software
part of the project

Jj=l

Buyer examines
a device

i£

f Payment J

too vague

too much

-v

too short

beyond

i.n

■4— >

m
u

u
□_

-lT

Jii-

Leave the
project

Table of
contents

Chapter
overview

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