74AC157 查看數據表（PDF） - Fairchild Semiconductor

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74AC157

Quad 2-Input Multiplexer

Fairchild Semiconductor 

Functional Description

The AC/ACT157 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 AC/ACT157 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:

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 AC/ACT157 is the moving of data

from two groups of registers to four common output bus-

ses. 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 AC/ACT157 can gener-

ate any four of the sixteen different functions of two vari-

ables with one variable common. This is useful for

implementing gating functions.

Truth Table

Inputs

E

S

I0

H

X

X

L

H

X

L

H

X

L

L

L

L

L

H

H = HIGH Voltage Level

L = LOW Voltage Level

X = Immaterial

Logic Diagram

Outputs

I1

Z

X

L

L

L

H

H

X

L

X

H

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

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