54LS257A DM54LS257B DM74LS257B 54LS258A DM54LS258B DM74LS258B
TRI-STATE Quad 2-Data Selectors Multiplexers
June 1989
54LS257A DM54LS257B DM74LS257B
54LS258A DM54LS258B DM74LS258B
TRI-STATE 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
Y
Y
Y
Y
Y
TRI-STATE versions LS157 and LS158 with same pin-
outs
Schottky-clamped for significant improvement in A-C
performance
Provides bus interface from multiple sources in high-
performance systems
Average propagation delay from data input 12 ns
Typical power dissipation
LS257B 50 mW
LS258B 35 mW
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 鈥?1
TL F 6417 鈥?2
Order Number 54LS257ADMQB 54LS257AFMQB
54LS257ALMQB DM54LS257BJ DM54LS257BW
DM74LS257BM or DM74LS257BN
See NS Package Number E20A J16A
M16A N16E or W16A
Order Number 54LS258ADMQB 54LS258AFMQB
54LS258ALMQB DM54LS258BJ DM54LS258BW
DM74LS258BM or DM74LS258BN
See NS Package Number E20A J16A
M16A N16E or W16A
Function Table
Inputs
Output
Control
H
L
L
L
L
Select
X
L
L
H
H
A
X
L
H
X
X
B
X
X
X
L
H
Output Y
LS257
Z
L
H
L
H
LS258
Z
H
L
H
L
H
e
High Level L
e
Low Level X
e
Don鈥檛 Care
Z
e
High Impedance (off)
TRI-STATE is a registered trademark of National Semiconductor Corporation
C
1995 National Semiconductor Corporation
TL F 6417
RRD-B30M105 Printed in U S A
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5
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