>
> Actually I wish to monitor a change from 'low' to 'high' of
> each RB4 ~ RB7. When this happen I would like to trigger some
> jobs in sequence. As a preliminary study of RB change ISR, I
> just output a string of character, say 'RB7 changed' to a LCD.
>

Then you want something a bit like this in your ISR

        movf    PORTB,W         ; which bits have changed?
        xorwf   OLD_PORTB,F

        ; now inspect the bits of OLD_PORTB,
        ; a bit is high if it changed on portb since last time we ran
        <add your inspection code here, branch as necessary>

        ; or, f you only want to know which bits changed from 0 -> 1
        ; ignoring which bits changed from 1 -> 0
        ; do this as well
        movf    PORTB,W
        andwf   OLD_PORTB,F

        ; and check the bits of OLD_PORTB here: a high indicates a bit that
was low before and is high now
        <add your inspection code here, branch as necessary>

        movf    PORTB,W         ; save this portb value for next change
comparison
        movwf   OLD_PORTB

You need to maintain a copy of what *used* to be in PORTB, define OLD_PORTB
as a global var. In your initialisation, you should read portb and write it
to this var before you enable interupts, else your first ISR call will be
junk


Jon

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