>The only problem I'd point out is the the 9500 series CPLD's drive only 8 mA
>per output and, unless you were planning to pair them up, i.e. use multiple
>pins tied together to drive the FD cable, you might have problems.
The biggest problem is with the outputs that'll drive the floppy disk bus.
Typically it's an open-collector output terminated to +5V with 150 ohms, so
you have to be able to sink 30 mA or so. So yes, this may be a concern.
(Or you can cheat and tie the lines high with "only" 220 or 300 or 470 ohms -
shouldn't be a big problem as long as there's only one drive on the bus.)
Do any CPLD's have "real" open-collector outputs, or can you fake it by
sending the output into tristate mode? (I'm asking this as a guy who's
never designed with CPLD's but does know 74XX00 series logic pretty
well.) I don't think it's an issue either way with exactly one controller
and one floppy drive on the bus.
--
Tim Shoppa Email: shoppa_at_trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
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Received on Tue Jul 04 2000 - 15:53:52 BST