Adrian Kennard <adrian@RHANNA.DEMON.CO.UK> wrote:

>On the topic of the port B int on a 16C84...
>
>Would I be right in thinking that setting or clearing B0-3 using bit
>operations would mean a port read and write and hence clear any pending
>interrupt for B4-7 change ?

    Adrian:

    No.  Interrupts set the RBIF flag; once set, that flag will trigger a
    jump to the interrupt vector as soon as its enable flag (RBIE) and GIE
    are both set.

    However...

    There's a major flaw in the Change-on-Port-B Interrupt logic.  If you
    read from Port B at the same instant that a change on RB4-7 occurs, the
    RBIF flag will NOT be set.  BSF/BCF instructions perform a read, of
    course, so if you ever do BCFs, BSFs, or any other Port-B read operation,
    you can pretty much forget about using the Change-on-Port-B interrupt.

    -Andy

--
Andrew Warren - fastfwd@ix.netcom.com
Fast Forward Engineering, Vista, California