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• Page 1
• Page 2
• Page 3
• Page 4
• Page 5: The PIC12C508A Instruction-Set
• Page 6: The PIC16F84 Instruction-Set
• Page 7: The Instruction-Set Explained

Introduction

This PIC Programming Course has been designed to get the BEGINNER into programming the PIC12C508A and PIC16F84 microcontrollers.
The ‘508A is the “baby” in the range with 6 lines that can be configured as input or output (GP3 can only be an input line) and the ‘F84 is the “one-and-a-half-port” version with 13 lines.
Both of these are very small devices in the “micro” world but they are the place to start.
Before starting this course we have prepared a discussion by Jim Brown BSc(Eng), HDipEdAd, GDE (Wits) on the PIC16F84 microcontroller. Just read the first 25% and come back to our course. You can gradually read the remainder later. Click HERE for the discussion.

The pin-out for the two chips we are covering in this course are as follows:

POWERING A PROJECT

All projects need to be powered from a power-source. This can be a battery, power-supply or even a set of solar-cells. Click HERE for an article on Powering A Project.

THE PIC’S

We have chosen these two out of the range of PIC devices as they are the cheapest and the best (for the beginner). You will see what we mean, AND AGREE, after you read the course.
Maybe you are wondering why we have produced so much information on programming these chips, as there is already an enormous amount available in books and on web sites.
The reason is the information is generally of a highly technical nature and not designed to get the REAL BEGINNER into programming. What is needed is an absolute beginners course. One that introduces the least amount of complication to get a program up-and-running.
And that’s what we have done. You don’t have to know Boolean Algebra, complex mathematics or the effect of double XOR’ing a file, to be able to program. We do everything in a simple way. The course also shows you how to interface the chips to external devices and by taking ideas from one project and applying them to another you can create a totally new circuit with the least amount of technical skill.
There’s an amazing thing about programming. A program can be constructed using highly complex thinking or very simple thinking. The end result is the same but the simple approach may take a few more instructions to achieve the end result. Who cares about a few more instructions when the micro is processing at 1,000,000 instructions per second!
We start off with a simple five-line program to turn on a LED with a PIC12C508A microcontroller.

SetUp   MOVLW 3E  ;Make GP0 output
        TRIS 06   ;Load TRISB file
Out0    MOVLW 01  ;Load W with 1
        MOVWF 06  ;Make GP0 HIGH
        GOTO Out0

This is the simplest program for the ‘508A. It turns on a LED as shown in the animation below:

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Click and hold down on the animation below and you will see it turn on the LED connected to GP0 (General Purpose IN-OUT line ZERO - Pin 7):

This is what the program is doing:
In the first two lines the input/output port is set-up so that the first line (GP0) is an output.
GP0 is turned ON and this will illuminate the LED connected to the line. The program goes to the fifth line and is sent back to the third line. Instructions 3, 4 and form a loop and the micro constantly executes these until the power is removed.
The diagram above is very simple. The power switch is turned ON and the LED illuminates.
You don’t need a microcontroller to turn on the LED but this is the simplest circuit to explain how the microcontroller operates.
The important point to note is the operation of the micro. It does not execute the 5 instructions in the program above, then stop. It keeps going as the oscillator inside the chip keeps operating all the time. The instruction-set for the PIC12C508A does not have a STOP or HALT instruction, so you must write the program so that the micro loops around a number of instructions. These instructions are sometimes called “do-nothing” instructions.
In the example above, the micro loops around instructions 3, 4 and 5, by executing 3, 4, 5, 3, 4, 5, 3, 4, 5, etc. The flowchart for the micro is shown below:

USING A PIC16F84

The same program can be written for the PIC16F84 microcontroller. Although the two chips do not have exactly the same set of instructions, about 90% of the instruction-set is the same and in this course we are going to concentrate on the instructions that are common to both chips.
The instruction to access lines GP0 to GP5, for the PIC12C508A are the same as accessing RB0 to RB5 for the PIC16F84 chip.
This means many of the programs and projects we will be presenting can be “burnt” into either chip.
“Burning” is an old name for “programming” and we use it to differentiate between the operation of writing a program - commonly called Programming, from the operation of downloading a program into a chip - also called Programming.
As soon as a project requires more than 5 or 6 lines (input/output lines) the PIC16F84 micro will be used.
But this is getting too advanced too quickly, getting back to the simplest program, it can be “burnt” or “downloaded ” into a PIC16F84 and the circuit below will turn on a LED.
The instruction: MOVWF 06 will turn ON (make HIGH) GP0 for a PIC12C508A or Line RB0 for a PIC16F84.
The PIC12C508A has an internal oscillator and no external components are required.
The PIC16F84 has some internal oscillator components and you must add the timing components (the resistor and capacitor). These two components are shown in the diagram below:

FLASHING A LED

Suppose you want to make the LED flash with an on-time of 0.1seconds and off-time=0.9seconds. This requires a 4-step program shown in the Flowchart below:

From the flow-chart you can see you need to do 4 things:

1. Turn ON an output
2. Keep the output ON for a period of time - called the Delay time
3. Turn OFF the output
4. Keep the output turned OFF for a period of time - called the Delay time

The thing you must remember is the processor (the heart of the microcontroller chip) must be kept running all the time. The PIC12C508A chip contains a 4MHz oscillator and this frequency is internally divided by 4 so that one instruction is processed every microsecond. This makes it very easy to produce accurate delay routines.
The PIC16F84 chip requires external components to complete the oscillator circuit. By using a 4k7 and 22p capacitor the oscillator circuit will operate a 4MHz.
In our example we can create a delay by knowing that each instruction takes 1 microsecond to execute or 2 microseconds if a branch is involved.
This means we need to produce a sub-routine of 100,000 “DO-NOTHING” cycles to create a delay of 0.1 seconds.
To produce a delay of 0.9 seconds, the delay above is called 9 times.
To create the routine needed to flash the LED, you can start from scratch by reading the notes we have provided in our chapters or go to the Library of Routines chapter. All the information you need to write a program on a template is contained on page 24 of this course. Click to download BlankF84.asm. With it you will be able to write programs on a text editor and run them in a PIC16F84. These are the lines of code you will need:

FlashLED1   BSF 03h,5     ;Select Page1
            MOVLW 00      ;to make GP0 output
            MOVWF 06
            BCF 03h,5     ;Select Page0
Loop1       BSF 06,0      ;SET bit0 HIGH
            CALL Delay1
            BCF 06,0      ;Make bit0 LOW
            MOVLW 09      ;Put 9 in W
            MOVWF 0C      ;0C is the loop file
AA1         CALL Delay1
            DECFSZ 0C
            GOTO AA1
            GOTO Loop1


Delay1      MOVLW 82h     ;130 loops
            MOVWF 1A
DelX        DECFSZ 1B     ;256 decrements
            GOTO DelX     ;2uS instruction
            DECFSZ 1A
            GOTO DelX
            RETLW 0

This program turns ON a LED for 0.1sec (Delay1 routine) then OFF for 0.9s by calling Delay1 nine times.

The following animation shows the result of burning the code into a ‘508A:

The program can be downloaded into a PIC16F84 and the circuit below will flash a LED:

But just before you rush out and do anything, you must understand that a PIC12c508A chip can only be burnt ONCE because the cells holding the program receive a charge during programming and this charge cannot be removed. The chip is guaranteed to hold a program for many years but you only use this chip when you are completely satisfied with a program and the project is ready for completion.

TWO CHIPS

This course concentrates on two chips. The PIC12C508A and PIC16F84. At the moment you don’t know how powerful these chips are and the type of projects they can drive. This knowledge will come “down the track” so we will explain our policy:
We firstly try to use a PIC12C508A for a project. If the project requires less than 5 input and/or output lines, the PIC12C508A will be suitable. If not, you will have to use the PIC16F84.
Programming a PIC16F84 is easy because it is programmed in the Multi Chip Programmer and placed in the project being developed.
If the project needs a PIC12C508A, you will need an adaptor. The adaptor holds a PIC16F84 and has oscillator components soldered to the pins. An 8-pin IC socket is soldered to the 18-pin socket and fits onto the project being developed. The PIC16F84 chip is taken out of the adaptor and “burnt” in the multi Chip Programmer. It is then placed into the adaptor and it functions exactly like a PIC12C508A chip.
When the program works perfectly, you can burn a real PIC12C508A chip and fit it to the project.
The diagram below shows how the adaptor holds the PIC16F84 chip and plugs into an 8-pin socket on the project you are developing.

This is the cheapest way to design a project with the PIC12C508A chip. Any other way is very expensive.
The PIC12C508A can only be programmed ONCE and the development of a project may take 50 or more “adjustments” until it is operating correctly. You can use 50 PIC12C508A chips or buy the EPROM version. These are very expensive and you will need at least 5 - 10 because they need to be erased for 20 minutes before a new program can be written into them and this slows down the time for development. You will also need an erasing lamp.
Our 8-pin to 18-pin adaptor costs very little and makes developing a program very simple.
You can program the PIC16F84 with instructions that suit the PIC12C508A and the program can be “burnt” into a PIC12C508A.
For the example we have used our Logic Probe project. This project takes an 8-pin PIC12C508A chip and by using the 8-pin to 18-pin adaptor and a PIC16F84, a program can be developed at almost NO COST.
One clever trick is to fit a PIC chip to an IC socket and keep the two together when transferring from the programmer to a project. The chip is much easier to get out of the socket (in the project) with your fingers. See photo below:

The PIC chip is fitted into an IC socket for easy removal during programming.

The diagram below shows the PICF84 being burnt on the Multi Chip Programmer, fitted to the 8-pin to 18-pin adaptor and plugged into the Logic Probe project.

Fitting the PIC chip (and IC socket) into the adaptor and into a project under development.

Why do we use the PIC12C508A?
The ‘508A is much cheaper than the ‘84 and if your project is very simple, it is ideal. Very small, cheap projects can be created with the PIC12C508A and this opens up a whole new field of projects.
The PIC16F84 can be programmed and erased over 1,000 times and is ideal for development work.
There are lots of projects designed around a PIC12C508A but the development costs are considerable if you don’t use our approach.
As you will read in the chapters, this course is entirely PRACTICAL and it gets you into programming at the least expense.
Because of this we have not used any of the “STAMP” concepts as they are very expensive and reduce the capability of the chip enormously.
Our aim is to get you into programming so you can produce microcontroller projects and sell programmed chips for as little as $5.00 each (in large quantities). This is something that has never been aimed-at before.
That’s why this course stands out from everything else.
As soon as you get into PIC programming, you should search the web for PIC user groups as they have a wealth of valuable information on their sites to help you understand PIC programming.
The chips we have chosen will allow you to get into creating projects equivalent to 6 or 8 chips (or even more in the old technology of gates and counters etc) and produce things such as electronic locks using card access, security tags that transmit up to a metre or so, displays, games, telephone devices, alarms, interfacing devices, oscillators, robotics and lots more. As one programmer said: “You will never use a 555 again!” Any of the ideas and projects that have already been produced on and for a “STAMP-type” module can now be created in a single chip and produced at less than 1/4 of the cost.
Surprisingly, our course will have enormous appeal to those already programming with one of these expensive modules. Quite often an idea will come up that is suitable for marketing. That’s when the project will have to be converted to a much cheaper design to make it marketable. And that’s where we step in. For the cost of a chip and a $5.00 prototyping PC board, you will be able to launch your own product. But obviously you will have to start at the beginning and familiarize yourself with the code and capabilities of the chip.
In the next section of this e-magazine we have designed a number of projects that use both chips. Some of the projects are simple while others are quite complex. However I can assure you they are less than half the complexity of a discrete design.
All the programming is “linear” (very simple) and by going through each line you will be able to see exactly what is being done at each step.
The biggest problem with the STAMP concept is the cost of duplication. The first prototype may cost $40 to $70 but additional copies will cost more than $20. With our approach a fully programmed chip can be sold by you for $5.00 to $8.00 (they cost as lost as $2 in large quantities), and an assembled PC board for less than $12.00. This gives you a head-start in the world of marketing and makes you competitive in manufacturing and selling your ideas.
Many will say the “STAMP concept” gets a program up and running with very few instructions but we have combated this by designing a set of routines to perform many of the operations you will require in the development of a program and placed them in a LIBRARY OF ROUTINES.
This chapter is included on this site. In this way you can get a program up and running with very little effort. The advantage of our approach is the micro runs at full speed, the program memory space can be fully utilized, no additional chips are required to store the program and all the input-output lines of the chip are available. There is really no comparison between the two concepts and the differences will not be mentioned again.
The biggest advantage of doing things our way is you are fully in-charge of the program. If something doesn’t work, you don’t have to wonder if the routine provided by the “STAMP or CLONE” is not doing the operation, or if your code has a bug. By directly using the micro’s instructions (from the set of approx 33 instructions) you can see exactly what is happening and why it’s not working.
This PIC course will be available in printed format very soon so you can have all the content at your fingertips. The book will cost $25.00 plus postage and its exact release date will be announced soon.
The book will be very popular as it is already 400 pages in size and this represents a lot of information to search on the web.