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Altera_Forum's avatar
Altera_Forum
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16 years ago

open-drain/open collector type of output

Hi All, This might have been discussed before, but I didn't see a definite answer. I have one IO pins which I wanna assign it to be a open-drain type. I tried to add the following attribute ...
Altera_Forum's avatar
Altera_Forum
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16 years ago

The Z80 busses I'm aware of, e.g. ECB don't use open collector data lines. ECB has LS245 type tri-state drivers. In so far there's no problem of too high pull-up resistance values. Of course, open collector can work for rather slow (a few MHz) busses, but I would expect 470 ohm to 1k pull-up level.

The drawback with open collector drivers is, that a sufficient current strength is required for all bus members, so you surely can't operate an unbuffered CMOS or MOS peripheral, which can still work with a not to heavily loaded tri-state bus.