Scott wrote:
>
> It seems to be working pretty well now, however when I use the rlf instruction
> the data is rolled into the high nibble of the variable temp and the carry nev
er
> sees is.  How can I make the temp variable four bits wide?    Thanks for havin
g
> mercy on such a newbi.

I think someone sneezed on the wafer before they cut it up and wrapped
the bits in prickly plastic. It's given your chip an extra instruction
:-)

The carry is always changed after a 'rrf' or rlf' instruction. It may
not appear to get changed, because the new data bit may be the same as
the old.

if PortA = 00000010, then

        movf porta,w
        movwf temp

temp = 00000010
carry could be 0 or 1 - it doesn't matter

        rrf temp

temp = 00000001 - [note: bit 7 is the original carry bit value and could
be 1]
carry = 0       - carry = original value of temp bit 0

carry = 0 -> key #1 not pressed, loop back and rotate again

        rrf temp

temp = 00000000 - bit 7 = the carry bit value
carry = 1       - carry = original value of temp bit 0

carry = 1 -> key #2 is pressed, service the key routine

Just looking over your message again, you mentioned "rlf" not "rrf". If
you changed this by accident that could be causing your problem.

Try using 55h or 0xAA in a register and rotate that left or right to see
the effect on the register and the carry bit.

--
Best regards

Tony

http://www.picnpoke.com
Email sales@picnpoke.com