On Mon, Aug 19, 2002 at 04:16:23PM -0700, Andrew Warren wrote:
> Dave Dribin <PICLIST@mitvma.mit.edu> wrote:
>
> > >     Twenty dollars says that the CRC is being calculated correctly,
> > >     but your serial-out routine (and whatever other junk you've put
> > >     between the PIC's registers and your eyes) is corrupting the
> > >     data that you see.
> >
> > I thought of that and have double checked the serial code.  The serial
> > routines do not to touch `crc_high' nor `crc_low'.
>
>     Right, that's exactly my point.
>
>     CRC_HI and CRC_LO are just fine, but your serial code (or your
>     one-byte-to-two-ASCII-hex-characters routine, or your PC
>     terminal program, or your serial-port settings, or whatever) is
>     showing the wrong information.

Ok, I see what you were getting at.  I added this code to the
beginning of my proggie:

        movlw   255
        movwf   count
        movlw   0
        movwf   byte
out_bytes:
        movfw   byte
        call    SerPrintHexByte
        call    SerPrintNewline
        incf    byte, f
        decfsz  count, f
         goto   out_bytes
        movfw   byte
        call    SerPrintHexByte
        call    SerPrintNewline

And sure enough, 00 through FF all come out ok.  No unexpected output.
This would seem to verify SerPrintHexByte.  I wrote a Perl script to
verify the results, rather than just eyeball it, too.

>     It's EXTRAORDINARILY unlikely that your serial routines are
>     corrupting any data... But if you want to know for certain, make
>     these changes to your code:

I tried this and sure enough, the same thing was printed both times.

I'm stumped. This makes no logical sense.  I've got to be missing
something here.  I guess this is where an ICE would help out, huh? :)
I'm just gonna dump this code, but at the same time I would like to
know what is the root cause of the problem here.

-Dave

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