[sdiy] Keyboard with PIC microcontroller

[simon.oo.o at xs4all.nl]

Hi Stefano,

kernel255\.mailinglis zei:
> Hi all,
> I have developed a small circuit to read keys of a keyboard with a PIC
> microcontroller. I have already developed the hardware, but I have some
> problem in developing the software with Assembler. I checked the PIC's CPU
> instructions and I haven't found any instruction to do indirect addressing
> or indexed addressing; I explain it by a simple C example:
>
> #define BufferSize 5
>
> char buffer[BufferSize],data,i;
> char *bufferPtr = buffer;
>
> for(i=0;i<BufferSize;i++)
> {
>     data = *(bufferPtr+i);
>     /* ... do something on data ... */
> }
>
> What I'm not able to do with PIC Assembler is to have a pointer to memory,
> increment it, and read or write the memory location pointed by it. I
> searched for a special register to do stuff like these (as append for
> other CPUs) but I haven't found it.

The index register in a PIC is called FSR.
The data it points to can be read and written via INDF.

Example:

   movlw  bufstart     ; bufstart defined as start address of buffer
   movwf  FSR          ; SFR now points to start of buffer
   movlw  d'5'
   movwf  count
Loop:
   movfw  INDF         ; get next byte
   call   Putchar      ; (or something)
   incf   FSR          ; increase pointer
   decfsz count
   goto   Loop


Vriendelijke groet,

Simon Brouwer
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