MC74AC157, MC74ACT157

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2

Figure 2. Logic Symbol

S

FUNCTIONAL DESCRIPTION

The

MC74AC157/74ACT157

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

MC74AC157/74ACT157 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:

A common use of the MC74AC157/74ACT157 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

MC74AC157/74ACT157 can generate any four of the

sixteen different functions of two variables with one

variable common. This is useful for implementing gating

functions.

Figure 3. Logic Diagram

E

S

NOTE:

This diagram is provided only for the understanding of logic

operations and should not be used to estimate propagation delays.