Bob Ammerman <PICLIST@MITVMA.MIT.EDU> wrote:

> Here is  a neat trick to get a 'push-pull' output from two PORT A
> pins:
>
> 1: define them as analog (ADCON1)
> 2: TRIS them as outputs.
>
> Now, when you BSF either of them the other will automatically be
> cleared.
>
> This would have been useful in a system I built that drove a piezo
> transducer directly off two PIC pins.

    Clever; I don't think I've ever seen that.

    Of course, if you can't configure the pins as analog inputs
    (because, for instance, the PIC you're using doesn't HAVE an A/D
    converter), you can do this:

        MOVLW   00000001B       ;RA0 = 1, RA1 = 0.
        MOVWF   PORTA           ;

        MOVLW   00000011B
        XORWF   PORTA           ;Toggle RA0 and RA1.
        XORWF   PORTA           ;Toggle the two pins again.
        XORWF   PORTA           ;And again...

    Or, if those two pins are the only ones defined as outputs on
    that port:

        MOVLW   00000001B       ;RA0 = 1, RA1 = 0.
        MOVWF   PORTA           ;

        COMF    PORTA           ;Toggle RA0 and RA1.
        COMF    PORTA           ;Again.
        COMF    PORTA           ;And again...

    -Andy


=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - San Diego, California
=== http://www.geocities.com/SiliconValley/2499

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