M74HC257

2/11

INPUT AND OUTPUT EQUIVALENT CIRCUIT

PIN DESCRIPTION

TRUTH TABLE

X : Don’t Care

Z : High Impedance

LOGIC DIAGRAM

This logic diagram has not be used to estimate propagation delays

PIN No

SYMBOL

NAME AND FUNCTION

1

SELECT

Common Data Select

Input

2, 5, 14, 11

1A to 4A

Data Input From Source A

3, 6, 13, 10

1B to 4B

Data Input From Source B

4, 7, 12, 9

1Y to 4Y

3 State Multiplexer

Outputs

15

OE

3 State Output Enable

Inputs (Active Low)

8

GND

Ground (0V)

16

Vcc

Positive Supply Voltage

INPUTS

OUTPUT

OE

SELECT

A

B

Y

HX

XX

Z

LLL

X

L

LL

H

X

H

LH

X

L

L

LH

X

H

H