I'm presently using portb to drive 3 seven seg displays, multiplexed
with common drives from porta 0,1 & 2.
I need an external interrupt, and I've tried using RB7, with poor
results, mainly due to determining the polarity of the interrupt signal.
I'd like to try RB0 as an interrupt, because of it's settable edge
triggering facility. (I need to interrupt on a falling edge only.)
However, when RB7 is not used as an interrupt, or anything else - it's
not connected - I only have to copy a full byte to the port, and it's
done. What happens to RB7 doesn't matter.
OK - but if I, say, configure RB0 as an input, the rest outputs, setup
RB) as an interrupt pin, set the edge triggering correctly, then get my
byte of data for the 7 segment led, and RLF once (garbage in bit0) and
then write it to portb, I'll be OK on the leds, but what's the effect on
RB0?
I've read a lot on this, and I may have attention deficiency syndrome
(an accute possibility) but I can't find out exactly what happens if you
write to an port bit that's configured as an input.  E.G. if the port
bit is held up, a byte is written to the whole port, and the bit in
question just happens to be low.  Does the port bit input buffer go low
momentarily, then get pulled back high again once the write operation is
over?  If it doesn't then OK, but if it does, would that trigger an
interrupt?
However, even if I don't have an interrupt problem looming, I'd like to
know what happens anyway.
Regards to you all,
Howard.

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