adastra wrote:
>
> I am writing a couple of thousand lines of code for 16c877 using the ICD.
> Well into the project, I have encountered some very strange problems
> involving data memory variables.  I have defined a list of them starting at
> 0x0020.  At some places in my program, I cannot seem to write to them, even
> though I THINK I have taken care with respect to the proper bank and page
> definitions.  For instance, in this case:
>
> calib   nop
>         banksel msg_nbr
>         movlw   .65             ;table address
>         movwf   msg_nbr
>         movwf   sp1
>
> The literal in w WILL be written to msg_nbr, but NOT to sp1.
>
> FWIW, msg_nbr is assembled at 0x0024 and sp1 is at 0x003D (using
> CBLOCK/ENDC.)  Curiously, if I reverse the placement of the variable names,
> the result reverses also.


The easiest check is to look at the *.lst file to make sure of the HEX
code produced. If it is correct and the bank select bit is right, then
the ICD must(?) be at fault.

00D4   00A4           00342         movwf msg_nbr
00D5   00BD           00343         movwf spl

Do you have both 'sp1' labels and 'spl' labels. They look the same, but
they aren't.

Is this actually doing what you think "banksel msg_nbr"

Try using this...

calib   nop
;        banksel msg_nbr
        clrf STATUS
        movlw   .65             ;table address
        movwf   msg_nbr
        movwf   sp1

If it now works, the banksel is somehow at fault. (unlikely)
If it still doesn't work, then good, msg_nbr or spl is defined wrong.

I actually got caught with a similar problem yesterday. I accidently
deleted a RAM definition, and while writing the upteenth code line I
used the same name as a label for a GOTO. It assembles and works ok, but
the results are weird.

Prior to that I spent 5 frustrating hours trying to find a bug that
turned out to be a BTFSC instruction that was supposed to be a BTFSS.

After awhile you begin to think that that little PIC has somehow come to
life and is out to get you. What you have to remember is the micro will
do exactly what you tell it to, not what you want it to.

Take a break for an hour and go for a brisk walk. You'd be amazed at the
bugs that suddenly jump out at you on your return.

I must remember to take that advice myself ;-)

--
Best regards

Tony

ICmicro's
http://www.picnpoke.com
mailto:sales@picnpoke.com

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