# Hex inverter floating outputs

For a project, I am connecting the output ports of a 74AC04E hex inverter to bnc ports.

Something could be (but not necessarily) be plugged in at one or more ports at a given time.

Should the ports have pull-up:s / pull-down:s or could they be left floating?

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Am I understanding correctly that the inputs will not be floating? –  Kevin Vermeer Nov 8 '10 at 16:12
@reemrevnivek - Yes, thats correct, the input is properly defined, and will not be floating. I should probably have noted that. –  Theodor Nov 9 '10 at 8:50

There is no problem in left the ports floating. If you want to insert a resistor (avoiding some high frequency noise problems) its better a pull down, as the IC has greater capacity to load a low level (8mA) than a high level (-0.4mA).

For a 5v a 47k ohms resistor would be ok (from datasheet min output resistance is 2k).

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Logic gates either have open drain outputs or push-pull. If it's open drain you need a pull-up to get a defined level when the output MOSFET is off. If it's on it will pull the output level low.
The 74AC04 has push-pull outputs. This isn't mentioned explicitely, but you can tell from the driving capabilities: "Outputs source/sink 24 mA". Push-pull outputs always have a defined output level, either 0V or $V_{DD}$, so you can leave them open.

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The outputs will never be 'floating', they'll always be driven by your IC, so you don't need to add pull-ups/downs.

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Perhaps they are trying to ask what state the outputs will be in if the inputs are left floating? –  mjh2007 Nov 8 '10 at 21:56
@mjh - Nope, the poster said the input is properly defined, and will not be floating. in a comment to the question. –  Kevin Vermeer Nov 9 '10 at 16:56