June 1989
54LS257A/DM54LS257B/DM74LS257B,
54LS258A/DM54LS258B/DM74LS258B
TRI-STATE Quad 2-Data Selectors/Multiplexers
Features
Y
É
General Description
TRI-STATE versions LS157 and LS158 with same pin-
outs
These Schottky-clamped high-performance multiplexers
feature TRI-STATE outputs that can interface directly with
data lines of bus-organized systems. With all but one of the
common outputs disabled (at a high impedance state), the
low impedance of the single enabled output will drive the
bus line to a high or low logic level. To minimize the possibil-
ity that two outputs will attempt to take a common bus to
opposite logic levels, the output enable circuitry is designed
such that the output disable times are shorter than the out-
put enable times.
Y
Y
Schottky-clamped for significant improvement in A-C
performance
Provides bus interface from multiple sources in high-
performance systems
Y
Y
Average propagation delay from data input 12 ns
Typical power dissipation
LS257B 50 mW
LS258B 35 mW
This TRI-STATE output feature means that n-bit (paralleled)
data selectors with up to 258 sources can be implemented
for data buses. It also permits the use of standard TTL reg-
isters for data retention throughout the system.
Y
Alternate military/aerospace devices (54LS257A/
54LS258A) are available. Contact a National Semicon-
ductor Sales Office/Distributor for specifications.
Connection Diagrams
Dual-In-Line Package
Dual-In-Line Package
TL/F/6417–2
Order Number 54LS258ADMQB, 54LS258AFMQB,
54LS258ALMQB, DM54LS258BJ, DM54LS258BW,
DM74LS258BM or DM74LS258BN
TL/F/6417–1
Order Number 54LS257ADMQB, 54LS257AFMQB,
54LS257ALMQB, DM54LS257BJ, DM54LS257BW,
DM74LS257BM or DM74LS257BN
See NS Package Number E20A, J16A,
M16A, N16E or W16A
See NS Package Number E20A, J16A,
M16A, N16E or W16A
Function Table
Inputs
Output
Control
Output Y
Select
A
B
LS257 LS258
H
L
L
L
L
X
L
L
H
H
X
L
H
X
X
X
X
X
L
Z
L
H
L
Z
H
L
H
L
H
H
e
e
e
High Impedance (off)
e
Low Level, X Don’t Care,
H
Z
High Level, L
TRI-STATEÉ is a registered trademark of National Semiconductor Corporation.
C
1995 National Semiconductor Corporation
TL/F/6417
RRD-B30M105/Printed in U. S. A.