Bob Blick wrote:
>
> Does anyone have a slick method for detecting rising or falling edges? I
> keep ending up with a variation of these two methods, and both seem cheesy.
> In this case I am trying to detect a falling edge on PORTA,4 and jump to
> Index_now. I am using index_flag for storage.
>

<code cut>

> Anybody got a quantum leap for me?
>

 Try this untested code:

        MOVF    PORTA,W         ;Get the current state of PORTA,4
        XORWF   index_flag,W    ;Compare to the saved state.
        ANDLW   1<<4            ;Only interested in PORTA,4

        SKPNZ
         goto   no_change

   ;Change in states was detected
        XORWF   index_flag,F    ;Save state for next time.

        ;"Index_now" code goes here.


no_change


You may get one spurious detection the first time through. If that's
really a problem, then initialize index_flag with the current state
of PORTA,4.


Check out a variation of this "edge-detection" algorithm in my
debouncing
algorithm:

http://www.interstice.com/~sdattalo/technical/software/pic/debounce.html


Scott