© 2000 Fairchild Semiconductor Corporation

DS006415

www.fairchildsemi.com

August 1986

Revised March 2000

DM74LS251

3-STATE 1-of-8 Line Data Selector/Multiplexer

General Description

These data selectors/multiplexers contain full on-chip

binary decoding to select one-of-eight data sources, and

feature a strobe-controlled 3-STATE output. The strobe

must be at a low logic level to enable these devices. The 3-

STATE outputs permit direct connection to a common bus.

When the strobe input is HIGH, both outputs are in a high-

impedance state in which both the upper and lower transis-

tors of each totem-pole output are OFF, and the output nei-

ther drives nor loads the bus significantly. When the strobe

is LOW, the outputs are activated and operate as standard

TTL totem-pole outputs.

To minimize the possibility that two outputs will attempt to

take a common bus to opposite logic levels, the output con-

trol circuitry is designed so that the average output disable

time is shorter than the average output enable time.

Features

s 3-STATE version of DM74LS151

s Interface directly with system bus

s Perform parallel-to-serial conversion

s Permit multiplexing from N-lines to one line

s Complementary outputs provide true and inverted data

s Maximum number of common outputs: 129

s Typical propagation delay time (D to Y): 17 ns

s Typical power dissipation: 35 mW

Ordering Code:

Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.

Connection Diagram

Function Table

H

= HIGH Logic Level

L

= LOW Logic Level

X

= Don't Care

Z

= High Impedance (OFF)

D0, D1…D7

= The level of the respective D input

Order Number

Package Number

Package Description

DM74LS251M

M16A

16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow

DM74LS251N

N16E

16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide

Inputs

Outputs

Select

Strobe

YW

CBA

S

XX

X

H

Z

Z

LL

L

L

D0

D0

LL

H

L

D1

D1

LH

L

L

D2

D2

LH

H

L

D3

D3

HL

L

L

D4

D4

HL

H

L

D5

D5

HH

L

L

D6

D6

HHH

L

D7

D7