TL/F/6417
54LS257A/DM54LS257B/DM74LS257B, 54LS258A/DM54LS258B/DM74LS258B
TRI-STATE Quad 2-Data Selectors/Multiplexers
June 1989
54LS257A/DM54LS257B/DM74LS257B,
54LS258A/DM54LS258B/DM74LS258B
TRI-STATE
É
Quad 2-Data Selectors/Multiplexers
General Description
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.
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.
Features
Y
TRI-STATE versions LS157 and LS158 with same pin-
outs
Y
Schottky-clamped for significant improvement in A-C
performance
Y
Provides bus interface from multiple sources in high-
performance systems
Y
Average propagation delay from data input 12 ns
Y
Typical power dissipation
LS257B 50 mW
LS258B 35 mW
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
TL/F/6417–1
Order Number 54LS257ADMQB, 54LS257AFMQB,
54LS257ALMQB, DM54LS257BJ, DM54LS257BW,
DM74LS257BM or DM74LS257BN
See NS Package Number E20A, J16A,
M16A, N16E or W16A
Dual-In-Line Package
TL/F/6417–2
Order Number 54LS258ADMQB, 54LS258AFMQB,
54LS258ALMQB, DM54LS258BJ, DM54LS258BW,
DM74LS258BM or DM74LS258BN
See NS Package Number E20A, J16A,
M16A, N16E or W16A
Function Table
Inputs Output Y
Output
Select A B LS257 LS258
Control
HXXXZZ
LLLXLH
LLHXHL
LHXLLH
LHXHHL
H
e
High Level, L
e
Low Level, X
e
Don’t Care,
Z
e
High Impedance (off)
TRI-STATE
É
is a registered trademark of National Semiconductor Corporation.
C
1995 National Semiconductor Corporation RRD-B30M105/Printed in U. S. A.
