On Friday, May 05, 2000 Kevin Blain wrote:
> I am having trouble with window detection - using the subwf function. It
> looks to me very much like the following code section should work, but then
> again, have I just been staring at it too long?

Looks like you did it right.

> I am using interrupts - Yes, I am preserving all the right registers, but
> could the C flag be getting corrupted is teh interrupt occurs during the
> skpc instruction???

Interrupt can't occur during skpc execution. Two cycle instructions
are executed actually in one cycle, the other cycle is dummy, during
which  the  next  instruction  is  fetched.  So  even  if  C flag gets
corrupted by interrupt, it can happen only between instructions.

Just make the registers saving/restoring in interrupt by the book and
you must be safe.

> For reference, device PIC16C72

> entry to routine is with ADRES freshly captured. That bit seems okay.

BTW, you can make the program a bit shorter:

        Radix = DEC

        movf ADRES, w   ;w = ADRES
        addlw  -176
;w  = ADRES - 176 = ADRES + (256 - 176) = ADRES + 80
        skpc
         goto SECTION_C ;ADRES < 176
;numbers 176-255 now start from 0
        addlw -(198-176)
;w = w - 22 = w + 234
        skpc
         goto SECTION_B ;176 <= ADRES < 198
;numbers 198-255 now start from 0
        addlw -(221-198)
        skpc
         goto SECTION_A ;198 <= ADRES < 221

Hint: ready to pack into a macro :)

<snip>

 Nikolai
 http://techref.massmind.org/member/NG--944