HD74AC157

Rev.2.00, Jul.16.2004, page 2 of 7

Logic Symbol

S

Pin Names

I

Source 0 Data Inputs

I

Source 1 Data Inputs

E

Enable Input

S

Select Input

Z

Outputs

Functional Description

The HD74AC157 is a quad 2-input multiplexer. It selects four bits of data from two sources under the control of a

common Select input (S). The Enable input (

E) is active-Low. when E is High, all of the outputs (Z) are forced Low

regardless of all other inputs. The HD74AC157 is the logic implementation of a 4-pole, 2-position switch where the

position of the switch is determined by the logic levels supplied to the Select input. The logic equations for the outputs

are shown below:

Z

Z

Z

Z

A common use of the HD74AC157 is the moving of data from two groups of register to four common output busses.

The particular register from which the data comes is determined by the state of the Select input. A less obvious use is

as a function generator. The HD74AC157 can generate any four of the sixteen different functions of two variables with

one variable common. This is useful for implementing gating functions.

Truth Table

Inputs

Output

ES

I

0

I

1

Z

H

XXX

L

LH

X

L

L

LH

X

H

H

LL

L

X

L

LL

H

X

H

H :

High Voltage Level

L

:

Low Voltage Level

X :

Immaterial