©1992 Fairchild Semiconductor Corporation

www.fairchildsemi.com

74VHC157 Rev. 1.2

2

Logic Symbols

IEEE/IEC

Truth Table

H

= HIGH Voltage Level

L

= LOW Voltage Level

X

= Immaterial

Functional Description

The VHC157 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 VHC157 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:

A common use of the VHC157 is the moving of data from

two groups of registers to four common output busses.

The particular register from which the data comes is

determined by the state of the Select input. A less obvi-

ous use is as a function generator. The VHC157 can

generate any four of the sixteen different functions of two

variables with one variable common. This is useful for

implementing gating functions.

Inputs

Outputs

E

Z

HX

X

X

L

LH

X

L

L

LH

X

H

H

LL

L

X

L

LL

H

X

H