5-54

FAST AND LS TTL DATA

SN54/74LS42

FUNCTIONAL DESCRIPTION

The LS42 decoder accepts four active HIGH BCD inputs

and provides ten mutually exclusive active LOW outputs, as

shown by logic symbol or diagram. The active LOW outputs

facilitate addressing other MSI units with LOW input enables.

The logic design of the LS42 ensures that all outputs

are HIGH when binary codes greater than nine are applied

to the inputs.

The most significant input A3 produces a useful inhibit func-

tion when the LS42 is used as a one-of-eight decoder. The A3

input can also be used as the Data input in an 8-output

demultiplexer application.

TRUTH TABLE

A0 A1 A2 A3 0

1

2

3

4

5

6

7

8

9

L

H

L

H

L

H

L

H

L

H

L

H

L

H

L

H

L

L

H

H

L

L

H

H

L

L

H

H

L

L

H

H

L

L

L

L

H

H

H

H

L

L

L

L

H

H

H

H

L

L

L

L

L

L

L

L

H

H

H

H

H

H

H

H

L

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

L

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

L

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

L

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

L

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

L

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

L

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

L

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

L

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

L

H

H

H

H

H

H

H = HIGH Voltage Level

L = LOW Voltage Level

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