what to do with 74HCxxx Control Pin ?

Hello
I don't know what should I do with 74HCxxx Control Pins
For example in 74HC245 , we have OE pin
Should I connect this pin directly to GND or with pull down resistor ?
and what's the value of pull down resistor ?
thanks a lot

Hi,

I assume you didn´t do a search in this form nor in the internet.
This really is a frequently asked question.

Try a search with "unused inputs". ;-)

Klaus

Golden rule - never leave pins floating.
In the specific case of control pins, they are there for a purpose, they change the way the device works so you must do something with them. Look at the data sheet for the device and see exactly what the pin does, then decide whether it should be tied high, tied low or actively driven.

In the case of the 74HC245, the OE pin effectively disconnects all the output pins so it can be wired to a bus. If it should be driving all the time, you can safely ground it so the outputs are permanently active, otherwise it should be driven from a logic level so it is only enabled when required. For most logic families, it doesn't matter whether you tie an input directly to supply or through a pull up/down resistor but adding a resistor can sometimes be helpful because it gives you a node you can temporarily change while testing or as a debugging aid.

Brian.