At 06:32 PM 10/21/00 -0600, Robert Rolf wrote:
>Does
> > anyone use the port change interrupt while they are changing the other bits
> > on that port?  Or is the port change interrupt still only useful for waking
> > the chip from sleep?
>
>It's useful, as long as you don't try to manipulate ANY other
>bits on the port.
>ALL instructions are read/modify/write so any attempt to change
>bits on the port causes a read, and that resets the bit change
>registers, so you can miss the change if it happens right
>at the moment you access the port.

So if I just WRITE the port, there shouldn't be a problem?  In other words,
the 3 lines that drive my shift registers are outputs only.  I can simply
write literals to the port to manipulate the lines as required.

The 3 control lines that drive this card are pretty much guaranteed to be
non-coincident.  Only one control line will ever change at a time (driven
from a CPLD).  So I could either use the 3 interrupts that are now
available to me or just use the port change interrupt only.  Hmm - same
board layout either way.  I'll try it!

My other choice was to write it for a 12c508 and sample the inputs at a
fairly high rate - every 12 uS or so.  Its not as much trouble as I had
initially thought.

dwayne



Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 16 years of Engineering Innovation (1984 - 2000)

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