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Which Micro and Why ?I use the PIC micro. The reason is simply "because I do". I've used it for quite a while now, it gets the job done, it's cheap, easy to get, I've got plenty of code already written, it's not worth changing to another micro. There are other popular hobby micros like the Atmel range. Most people religously recommend one or the other, but it really doesn't matter. For most relatively simple hobby or low volume applications it makes about as much difference as favorite colour.
This is a common question but it's too general. Smaller more specific questions are easier to answer. The first thing to do is: Search the Internet. Even if this doesn't provide the answers it should narrow the questions a bit.
A Quick IntroductionYou don't have to be able to read Binary or HEX but it's all part of the bigger picture. I don't know of any simple or getting started assembly language tutorials. Motorola put out a good book called "M68HC05 Applications Guide". It's for their HC05 micro but that doesn't matter too much for the basics. I think you can download it (Google search). ASM (Assembly Language)ASM requires that you know what's inside the micro in the form of registers and hardware features. The guts of assembly programming is the same for all micros but the individual micros "workings" determine how you apply it. The best way to start is probably to get a development kit or at least some chips, a board to run it on and a way of loading the program (a programmer).
Microchip provide free a development pacakge for the PICs called MPLAB. This includes the editor and assembler, and has some advanced features for later on. The assembler produces a "hex or s19" output file that the programmer loads into the chip. You create a simple acsii text source file containing the assembly program source code. The assembler program creates output files including a listing of the assembled program and a file containing the raw code that gets programmed into the PIC. Example to pulse an LED for a short time:This is a simple example that produces one pulse of an LED connected to PORT-B of the PIC. It occupies only 7 memory locations within the program memory of the PIC. This program assumes that you have already defined a few things earlier in the asm source file. These definitions tell the assembler program where port-b and the timer variable GPTIM1 are located within the PIC and which port-b pin the LED is connected to. |
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label |
instruction |
comment |
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FLASH |
bsf |
portb,led |
; turn on the LED connected to portb |
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movlw |
250d |
; load W with 250 decimal (sets pulse length) |
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movwf |
GPTIM1 |
; copy W to GPTIM1 |
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FL_1 |
decfsz |
GPTIM1 |
; count -1 and end if zero otherwise loop |
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goto |
FL_1 |
; loop back and -1 again |
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bcf |
portb,led |
; turn off the LED connected to portb |
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FINISH |
goto |
FINISH |
; program stops here in an endless loop |
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end |
; end of program |
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To make the asm source file more readable we assign labels to things like port-b and the LED. This measn that we don't have to remember all the numbers that would otherwise refer to the specifics of the PIC and the way it's connected. The assembler program reads the assignments and definitions and works through the asm instructions of the source file swapping things about and doing lots of lookups and exchanges to produce the specific instruction codes that go into the PIC program memory. There are usually some instructions inthe source file that are not actually PIC instructions but are there to tell the assembler program what to do. These are called assembler directives. The actual PIC asm instructions are described in the data sheet for the micro which can be downloaded from the Microchip website. There are also lots of examples and applications notes. The next step:
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last updated: 16 July 2004 |