Open drain and push-pull

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Yes....I know.....basic......but I have to ask what this termology means in
the form of changing a pin on a processor from an open drain to a push
pull...thanks....



Re: Open drain and push-pull
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An open drain can only sink current.  You use it for wired-OR bus connections.
It requires an external pull-up resistor.

A push/pull can source or sink current.  It MAY OR MAY NOT have a third
high-impedance state in which it does neither.

A push/pull does not require an external pull-up resistor UNLESS it also
supports the high-impedance state.

You generally will only use the tri-state ones for bus connections.  You can tie
many tri-state outputs together, sharing a pull-up, but you have to be careful
to make certain that you don't have two of them trying to drive the bus in
different directions at the same time.



Re: Open drain and push-pull
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Think of a SPDT switch.  The arm is the output pin.  Connect the
lower terminal to ground, and leave the upper terminal open.  You
have an open drain output.  Connect the upper terminal to the plus
logic voltage.  You have a push pull output.

    +V (or open) ---------o 1
                          -----o-----------> output.
    GND ------------------o 0

--
Chuck F ( snipped-for-privacy@yahoo.com) ( snipped-for-privacy@worldnet.att.net)
   Available for consulting/temporary embedded and systems.
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