7 Jul
2006
7 Jul
'06
9:55 p.m.
On Friday 07 July 2006 07:58 pm, Tony Duell wrote:
Oh really? I've never heard _that_ before about these parts... Do you know
offhand if that's the case for other brands as well? I believe I have some
NEC parts around somewhere.
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.
I sure have enough of those, too, and 6526s as well. No idea how hard it
would be to interface one of those parts to a bus that's not made for it but
I believe I've seen it done -- if I'm remembering right the Osborne 1 used a
68xx chip for something, it's been ages since I looked at the schematics,
but that at least tells me that it's possible.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin