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PDF DM74LS257 Data sheet ( Hoja de datos )

Número de pieza DM74LS257
Descripción (DM74LS257 / DM74LS258) TRI-STATE Quad 2-Data Selectors/Multiplexers
Fabricantes National Semiconductor 
Logotipo National Semiconductor Logotipo



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No Preview Available ! DM74LS257 Hoja de datos, Descripción, Manual

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 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
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
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
Control
Select
A
B
LS257
LS258
H
X XX Z
Z
L
L LX L
H
L
L HX H
L
L
H XL L
H
L
H XH H
L
H e High Level L e Low Level X e Don’t Care
Z e High Impedance (off)
TRI-STATE is a registered trademark of National Semiconductor Corporation
C1995 National Semiconductor Corporation TL F 6417
RRD-B30M105 Printed in U S A

1 page




DM74LS257 pdf
Logic Diagrams
LS257B
LS258B
TL F 6417 – 3
TL F 6417 – 4
5

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