www.fairchildsemi.com

2

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 com-

mon 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 sup-

plied 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 obvious 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.

Logic Diagram

Please note that this diagram is provided only for the understanding of logic operations and should not be used to estimate propagation delays.

Inputs

Outputs

E

Z

HX

X

X

L

LH

X

L

L

LH

X

H

H

LL

L

X

L

LL

H

X

H