What are the "Enable Input" pins on a decoder?

I'm trying to multiplex with an arduino and a 74HC238N decoder. on the datasheet I was looking at I saw that besides the 8 outputs, 3 inputs, GND and Vcc there were also 3 "Inable Input" pins, that I couldn't figure out what they do. Can somebody please explain?

Picture of What are the
The enable pins are used to switch ON the output pins. Logic chips have THREE states for their outputs, "0", "1" and "Tri-state". WHen they are outputting a "0", the output is switched towards the ground line. When they output a "1", the output is switched to the supply line. When the output is tri-state the output pin "FLOATS", and is what we call "high-impedance".

Its an important feature: it means that pins can share lines with other chips, and their outputs don't fight - in some ancient computer designs, it was possible to connect outputs set to 0 with outputs set to 1 and start a fire !!!
yonch (author)  steveastrouk4 years ago