DM54LS251 DM74LS251 TRI-STATE Data Selectors Multiplexers
June 1989
DM54LS251 DM74LS251
TRI-STATE Data Selectors Multiplexers
General Description
These data selectors multiplexers contain full on-chip bina-
ry decoding to select one-of-eight data sources and feature
a strobe-controlled TRI-STATE output The strobe must be
at a low logic level to enable these devices The TRI-STATE
outputs permit direct connection to a common bus When
the strobe input is high both outputs are in a high-imped-
ance 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 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
Y
Y
Y
Y
Y
Y
Y
Y
TRI-STATE version of LS151
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
54LS 49
74LS 129
Typical propagation delay time (D to Y)
54LS 17 ns
74LS 17 ns
Typical power dissipation
54LS 35 mW
74LS 35 mW
Connection Diagram
Dual-In-Line Package
Function Table
Inputs
Select
C
X
L
L
L
L
H
H
H
H
B
X
L
L
H
H
L
L
H
H
A
X
L
H
L
H
L
H
L
H
Strobe
S
H
L
L
L
L
L
L
L
L
Outputs
Y
Z
D0
D1
D2
D3
D4
D5
D6
D7
W
Z
D0
D1
D2
D3
D4
D5
D6
D7
H
e
High Logic Level L
e
Low Logic Level
X
e
Don鈥檛 Care Z
e
High Impedance (Off)
D0 D1
D7
e
The level of the respective D input
TL F 6415 鈥?1
Order Number DM54LS251J DM54LS251W
DM74LS251M or DM74LS251N
See NS Package Number J16A M16A N16E or W16A
TRI-STATE is a registered trademark of National Semiconductor Corporation
C
1995 National Semiconductor Corporation
TL F 6415
RRD-B30M105 Printed in U S A
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