A mechanical switch will "open and close" literally thousands of times each
time you actually close the switch or open the switch. This is due to the
mechanical contacts rubbing together (settling) closed or opening. Don't
forget, you're sampling the open or closed position many times during that
time period without a delay.
Rick

Rafael Vidal Aroca wrote:

>         Hi, i tried this example on PIC16F84, that counts the number of
> changes on a switch. It's easy to understand the btfss and btfsc parts
> that waits for changes on the switch and then adds the change to the
> counter.
>
>         But i didn't realize why we need to delay a bit (ANTIREBOND) when
> the switch is changed. According to the example's text, it's because of
> mechanical problems of switches...anyone could give me a better
> explanation for the need of this delay?
>
> LOOP            btfss   PORTA,0
>                 goto    LOOP
>                 call    ANTIREBOND
>
> LOOP2           btfsc   PORTA,0
>                 goto    LOOP2
>                 call    ANTIREBOND
>
>                 incf    COUNTER,f
>                 movf    COUNTER,w
>                 movwf   PORTB
>
>                 goto LOOP
>
> ANTIREBOND      bcf     INTCON,2
>
>                 movlw   0xB0
>
>                 movwf   OPTION_REG
>
> DEL             btfss   INTCON,2
>                 goto    DEL
>                 return
>
> []s Rafael.
> http://grad.icmc.sc.usp.br/~rva
>
> --

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics