7 Jul
2006
7 Jul
'06
4:58 p.m.
If you have an 8255-based data acquisition board kicking around (they're
not uncommon), that might be a good "universal" solution, giving you a few
more I/Os and latched input and output.
The problem is that the 8255 is fundamnetally broken as designed (well,
I'd expect that from Intel, alas). Any write to the mode control register
clears all outputs to 0's. Which means you can't reverse the direstion of
one of the 8 bit ports without mucking up everything else.
Yes, I know about the bidirexctional mode (Mode 2 IIRC). But to use that
in a lot of cases is a kludge too. Personally I'd rather link a 6522 or
similar to the ISA bus.
-tony