Fairchild Semiconductor DM74LS251N, DM74LS251MX, DM74LS251M, DM74LS251CW Datasheet

© 2000 Fairchild Semiconductor Corporation DS006415 www.fairchildsemi.com

August 1986
Revised March 2000

DM74LS251 3-STATE 1-of-8 Line Data Selector/Multiplexer

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-o f-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 3­STATE outputs permit direct connection to a common bus.
When the strobe input is HIGH , both out put s are in a hig h­impedance state in which both the upper and lower transis­tors of each totem-pole output are OFF, and the output nei­ther drives nor loads the bus significantly. When the strobe
is LOW, the outputs are activa ted a nd op era te 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 con­trol circuitry is designed so th at the ave rage ou tput disa ble
time is shorter than the average output enable time.

Features

■ 3-STATE version of DM74LS151

■ Interface directly with system bus

■ Perform parallel-to-serial conversion

■ Permit multiplexing from N-lines to one line

■ Complementary outputs provide true and inverted data

■ Maximum number of common outputs: 129

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

■ Typical power dissipation: 35 mW

Ordering Code:

Devices also availab le in Tape and Reel. Specify by appending th e s uffix let t er “X” to the ordering code.

Connection Diagram Function Table

H = HIGH Logic Level
L = LOW Logic Level
X = Don't Care
Z = High Impedance (OF F )
D0, D1…D7 = The level of the respe ctiv e D input

Order Number Package Number Package Description

DM74LS251M M16A 16-Lead Small Outline Integrated Circuit (SOIC), JED EC 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

XXX H Z Z
LLL L D0D0
LLH L D1D1
LHL L D2D2
LHH L D3D3
HLL L D4D4
HLH L D5D5
HHL L D6D6
HHH L D7D7

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DM74LS251

Logic Diagram