At 22:07 07.7.1997 EST, you wrote:
>Easy Question (for you pro's): I want to read a non-interrupt driven
>port on a PIC16C74 and detect a rising or falling edge. Any ideas on
>the best way to implement this? I'm quite the rookie here -this is
>my first design. Reasoning tells me to :
>
>               Read the port
>               Store it's value
>               Read it again
>               Compare the values
>
>If the values are different - i've detected the edge change. Does
>this make sense? How could I implement this in C?
>
>Thanks -
>
>

Hi Daniel,
u can try this:

loop
        movf    last,w          ; load last port value
        movwf   work            ; move it to work register
        movf    port,w          ; load port value
        movwf   last            ; move to last register
        xorwf   work,f          ; exlusive OR port value with last port value
                                ; compare is done, last port status is stored

;       btfsc   status,z
;       goto    loop            ; if no change, go to loop

        btfsc   work,0
        goto    do_0            ; if port,0 is changed do 0
        btfsc   work,1
        goto    do_1            ; if port,1 is changed do 1
        .....
        goto    loop            ; port is not changed, go to begining
do_0
        ......
        goto    loop            ; 0 is done, go to begining
do_1
        ......
        goto    loop            ; 1 is done, go to begining


Cheers,
Chris B.