>I have implemented portB with inputs and outputs, the inputs configured "to
>interrupt on change" as i require, I am monitoring for stray interrupts
>(using leds) and so far, emphasis on so far no random problems/errors,

As I said, if you want to use them as general interrupts, disabling them
during portions of the code that use PORTB I/O and re-enabling them during
portions that don't use PORTB access, that's fine.  The only problem with
this is that for many people, trying to isolate portions of the code that
allow interrupt on change from portions that use PORTB for I/O (can't allow
interrupt on change) is very tough.  That's not to say it can't be done, but
unless you're really desperate for interrupt sources and have your code
sectioned off safely, you might as well poll the lines rather than try to
use the interrupts.

For example, if you have PORTB interrupt on change enabled for RB<4:7> and
somewhere in your code you proceed to set RB<2> (output), the entire port
gets read, bit 2 latch is set, and the entire port is written.  During the
read cycle (Q2), if one of your interrupt pins detects a change, it will be
ignored because the PORTB read is in process and the latches are re-written
with the new value.  So, the interrupt on change comparison shows "no
change."

From the 16C71 datasheet again:

"Note: For the PIC16C71
If a change on the I/O pin should occur
when the read operation is being executed
(start of the Q2 cycle), then interrupt flag bit
RBIF may not get set."

Granted, I'm not sure if this note applies to ALL PICs, but it should be
noted anyways.  I can't imagine the bug would only exist on the 'C71 since
the same architecture is used for PORT I/O.  The 'F876 datasheet also
cautions against polling PORTB during int. on change enable.  It also
references Microchip's AN552, which may contain more information.

--Andrew
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