5-269

FAST AND LS TTL DATA

SN54/74LS157

FUNCTIONAL DESCRIPTION

The LS157 is a Quad 2-Input Multiplexer fabricated with the

Schottky barrier diode process for high speed. 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 LS157 is the logic implementation of a 4-pole,

2-position switch where the position of the switch is deter-

mined by the logic levels supplied to the Select Input. The logic

equations for the outputs are:

Za = E ⋅ (I1a ⋅ S + I0a ⋅ S)

Zb = E ⋅ (I1b ⋅ S + I0b ⋅ S)

Zc = E ⋅ (I1c ⋅ S + I0c ⋅ S)

Zd = E ⋅ (I1d ⋅ S + I0d ⋅ S)

A common use of the LS157 is the moving of data from two

groups of registers to four common output busses. The partic-

ular 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 LS157 can generate any four of the 16 different

functions of two variables with one variable common. This is

useful for implementing highly irregular logic.

TRUTH TABLE

ENABLE

SELECT

INPUT

INPUTS

OUTPUT

E

S

I0

I1

Z

H

X

X

X

L

L

H

X

L

L

L

H

X

H

H

L

L

L

X

L

L

L

H

X

H

H = HIGH Voltage Level

L = LOW Voltage Level

X = Don’t Care

GUARANTEED OPERATING RANGES

Symbol

Parameter

Min

Typ

Max

Unit

VCC

Supply Voltage

54

74

4.5

4.75

5.0

5.0

5.5

5.25

V

TA

Operating Ambient Temperature Range

54

74

– 55

0

25

25

125

70

°C

IOH

Output Current — High

54, 74

– 0.4

mA

IOL

Output Current — Low

54

74

4.0

8.0

mA