[Coco] OT: electronics question
theother_bob at yahoo.com
Thu May 27 00:49:45 EDT 2004
--- James Dessart <james at skwirl.ca> wrote:
> On 26-May-04, at 1:26 AM, Bob wrote:
> > If either input is high, the output should be low. Short both inputs
> > to ground
> > and the output should go high. I assume you have the pinout for this
> > quad NOR
> > gate.
> I shorted them both to ground, and it worked. I'm guessing that they
> stay high when they're unconnected.
Actually, it's kind of indeterminate... you can't count on it being one or the
other without applying a specific input. That's why they use either pull-up or
pull-down resistors, especially if being fed by tri-state chips. The third
output state is basically disconnected. This is needed for things like data
buses which could be fed by multiple sources... it's bad to connect 2 outputs
together, so you'd either need a ton of diodes for protection or tri-state
outputs, obviously the cheaper and neater solution.
(shouts from way out in left-field "throow mee the ballll!")
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