What is the enable pin on a multiplexer?

I am thinking of using this http://www.ti.com/lit/ds/symlink/cd74hc151.pdf to read multiple encoder outputs into one pin on the Atmega328P. It has an enable pin, what's it for and how is it used?

It acts as a global on/off switch for all the inputs and outputs. You will notice that it has a bar (-) over the E, which means 'not enable', in other words, when it is high it disables the inputs and outputs. If you don't need it tie it to 0V, which turns it on permanently. If you look at the truth table on page 2 you will see that with not enable high the output Y is always low, regardless of the other inputs.

EDIT
For some reason I1 in the truth table has a bar over it, which suggests that it is inverting, however, looking at the truth table suggests it is not inverting. I think I1 having a bar over it is a mistake.

Take a look at the "Functional diagram" in the link You attached!

You can in fact, connect more than one multiplexer with the same "common" line and enable only one of them at a time, in order to have a wider selection.

This avoids "chaining" them with the common of one coming from one selection of another, which loses one selection and introduces twice the path resistance.

Just throwin’ the idea out there: I2C encoder.

shai:
I am thinking of using this http://www.ti.com/lit/ds/symlink/cd74hc151.pdf to read multiple encoder outputs into one pin on the Atmega328P. It has an enable pin, what's it for and how is it used?

How many outputs do each of the encoders have?
How many encoders? Can you post link to specs/data please?

Do you need to read direction as well as pulses from the encoder?
Tom... :slight_smile:

TomGeorge:
How many outputs do each of the encoders have?
How many encoders? Can you post link to specs/data please?

Do you need to read direction as well as pulses from the encoder?

Don't you love it when people scatter around the information of their project?