Re: Converting 6502 Asm to PIC

[PIC Newbie <allenbsf6502@gmail.com>]

On Nov 25, 1:06 pm, Toinet <antoine.vig...@laposte.net> wrote:
> On 24 nov, 23:30, PIC Newbie <allenbsf6...@gmail.com> wrote:
>
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> > MESSAGE STR 'APPLE 2 FOREVER'
>
> > MAIN  LDX #1     ;POINT TO FIRST ASC
> > MESSLOOP:
> >       LDA MESSAGE,X
> >       CMP $32
> >       BNE CONV
> > SPACE JSR INT_WORD_DLY   ;DELAY 6 DOT ELEMENTS ~500MS
> >       CLC
> >       BCC SPACE_OK
> > CONV  JSR CONVERT        ;CONVERT ALPHA-NUMERIC TO INDEX
> > SPACE_OK:
> >       INX
> >       CPX #MESSAGE+1     ;END OF MESSAGE?
> >       BCC MESSLOOP
> >       RTS
>
> > TIA,
>
> > Allen
>
> I would have written...
> SPACE_OK:
>       INX
>       CPX MESSAGE     ;END OF MESSAGE?
>       BCC MESSLOOP
>       RTS
> ...instead of CPX #MESSAGE+1.
> The length of the string is saved in the first byte of MESSAGE not the
> second. Unless this is due to the assembler but I doubt it.
>
> I have another question regarding $32. Is there a useful info saved on
> zero page offset $32 or is it the space character (#32 or #$20)?
>
> Thank you,
> antoine- Hide quoted text -
>
> - Show quoted text -

Yes, you are absolutely right.  After checking the object code
generating.  I found out the result wasn't what I was expecting.  I
thought CPX #MESSAGE+1 should give me the "content of message" + 1,
and it ended up as the lower byte address of (Message + 1).  $32 is a
typo, it should be #' '.  thanks for pointing out my mistakes.  The
corrected one is as below:


  ORG $800
;using LISA 2.5 by Randy Hyde

   JMP main
MESSAGE STR 'APPLE 2 FOREVER'

;str will generate the message in normal ASC with the number of
characters as the first byte

MAIN  LDX #0     ;POINT TO FIRST ASC
MESSLOOP:
      LDA MESSAGE+1,X
      CMP #32
      BNE CONV
SPACE JSR INT_WORD_DLY   ;DELAY 6 DOT ELEMENTS ~500MS
      CLC
      BCC SPACE_OK
CONV  JSR CONVERT        ;CONVERT ALPHA-NUMERIC TO INDEX
SPACE_OK:
      INX
      CPX MESSAGE        ;END OF MESSAGE?
      BCC MESSLOOP
      RTS

Allen