On Mon, 23 Mar 1998 16:41:44 -0500 myke predko <myke@PASSPORT.CA> writes:

>This is why I use the code:
>
>  movlw   1
>  subwf   Count
>  btfss   STATUS, C             ;  If Carry Not Set, Then Gone from 0
>to 0x0FF
>   decf   Count+1

You could also use this routine, which doesn't affect W or C:
        movf    Count,f         ;Test if LSB is zero -- if so,
set Z.
        btfsc   STATUS,Z        ; If low byte won't roll under,
don't
        decf    Count+1,f       ;  need to dec. high.
        decf    Count,f         ;Always dec. low byte.

But it doesn't have a good way to tell if the decremented Count is now
zero.  After Myke's routine, the Z flag will be set when both bytes of
Count are zero(i.e. if Count was 0001 before the routine).  Myke's
routine can also be modified to detect when the count rolls under past
zero by replacing the decf of the high byte with another subwf.  In this
case, the C flag will be clear only if Count is now FFFF (was 0000 on
entry), and the Z flag test for zero will also still work.


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