DM74LS257BN
3-STATE Quad 2-Data Selectors/Multiplexers

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Datasheet

Size: 56.55KB
Page: 5
PDF: DM74LS257BN.pdf
  • Description:
    3-STATE Quad 2-Data Selectors/Multiplexers
  • MFG:
    FAIRCHILD [Fairchild Semiconductor]
 

Abstract


? 1999 Fairchild Semiconductor Corporation DS006417 www.fairchildsemi.com
June 1989
Revised November 1999
DM74LS257
B
3-
ST
A
T
E Q
u
ad

2-
Data Sele
ctor
s/Mul
t
i
p
lexer
s
DM74LS257B
3-STATE Quad 2-Data Selectors/Multiplexers
General Description
These Schottky-clamped high-performance multiplexers
feature 3-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 pos-
sibility 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 output enable times.
This 3-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
a73 3-STATE versions LS157 and LS158 with same pinouts
a73 Schottky-clamped for significant improvement in A-C
performance
a73 Provides bus interface from multiple sources in
high-performance systems
a73 Average propagation delay from data input 12 ns
a73 Typical power dissipation: 50 mW

Ordering Code:
Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
Connection Diagram
Function Table
H = HIGH Level X = Don’t Care
L = LOW Level Z = High Impedance (off)
Logic Diagram
Order Number Package Number Package Description
DM74LS257BM M16A 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
DM74LS257BN N16E 16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
Inputs Output Y
Output
Select A B LS257
Control
HXXXZ
LLL L
HXH
LHXLL
HH

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