Thanks Olin, I see your point..



Hi All,=20

I'm new to PICs and am trying to "port" my Z80 assembler skills to
something that belongs in this century but am having problems with my
test program.

Here it is:
          LIST p=3D16f877,c=3D140
        include "p16f877.inc"


          org   0
        clrf    STATUS
        goto    BootStart
        org     4
ISR     goto    5               ; Setup Interupt Address
          org   5


BootStart
          clrf          PORTB

        bsf     STATUS,RP0      ; set RAM Page 1 for TRIS registers
        movlw   b'00000000'
        movwf     TRISB             ; set PORTB for all outputs

        bcf     STATUS,RP0      ; back to RAM page 0


LoopAgain
        ;movlw   0x00
        ;movwf   PORTB              ; All PORTB bits off
        ;movlw   0xFF
        ;movwf   PORTB              ; All PORTB bits on

        incf    W, 0                ; W =3D W + 1
        movwf   PORTB               ; PORTB =3D W
        goto    LoopAgain

        end=20

Now I thought that 'incf W, 0' would perform a W=3DW+1 operation, and =
that
when it reached 255, it would simply start from 0 (since it's an 8-bit
register), but this doesn't seem to be the case.

If I use the 4 commented lines instead of the 3 lower ones, then I get a
nice square wave on all 8 I/O pins, so I know the PIC is working and
that my programmer is ok etc.
All I expect the above test program to do is count in binary flashing 8
LEDs....

So what stupid thing am I doing wrong...

Any help much appreciated,

Joe

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