5-429

FAST AND LS TTL DATA

SN54/74LS257B

D SN54/74LS258B

FUNCTIONAL DESCRIPTION

The LS257B and LS258B are Quad 2-Input Multiplexers

with 3-state outputs. They select four bits of data from two

sources each under control of a Common Data Select Input.

When the Select Input is LOW, the I0 inputs are selected and

when Select is HIGH, the I1 inputs are selected. The data on

the selected inputs appears at the outputs in true (non-

inverted) form for the LS257B and in the inverted form for the

LS258B.

The LS257B and LS258B are 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:

LS257B

Za = E0 • (I1a • S + I0a • S) Zb = E0 • (I1b • S + I0b • S)

Zc = E0 • (I1c • S + I0c • S) Zd = E0 • (I1d • S + I0d • S)

When the Output Enable Input (E0) is HIGH, the outputs are

forced to a high impedance “off” state. If the outputs are tied

together, all but one device must be in the high impedance

state to avoid high currents that would exceed the maximum

ratings. Designers should ensure that Output Enable signals

to 3-state devices whose outputs are tied together are

designed so there is no overlap.

LS258B

Za = E0 • (I1a • S + I0a • S) Zb = E0 • (I1b • S + I0b • S)

Zc = E0 • (I1c • S + I0c • S) Zd = E0 • (I1d • S + I0d • S)

TRUTH TABLE

OUTPUT

ENABLE

SELECT

INPUT

DATA

INPUTS

OUTPUTS

LS257B

OUTPUTS

LS258B

EO

S

I0

I1

Z

Z

H

X

X

X

(Z)

(Z)

L

H

X

L

L

H

L

H

X

H

H

L

L

L

L

X

L

H

L

L

H

X

H

L

H = HIGH Voltage Level

L = LOW Voltage Level

X = Don’t Care

(Z) = High Impedance (off)

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

– 1.0

– 2.6

mA

IOL

Output Current — Low

54

74

12

24

mA