SN54ALS138A, SN54AS138, SN74ALS138A, SN74AS138
3-LINE TO 8-LINE DECODERS/DEMULTIPLEXERS
SDAS055E – APRIL 1982 – REVISED JULY 1996
SN54ALS138A, SN54AS138 . . . J PACKAGE
SN74ALS138A, SN74AS138 . . . D OR N PACKAGE
Designed Specifically for High-Speed
Memory Decoders and Data Transmission
Systems
(TOP VIEW)
Incorporate Three Enable Inputs to Simplify
Cascading and/or Data Reception
A
B
C
V
CC
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
Y0
Y1
Y2
Y3
Y4
Y5
Y6
Package Options Include Plastic
Small-Outline (D) Packages, Ceramic Chip
Carriers (FK), and Standard Plastic (N) and
Ceramic (J) 300-mil DIPs
G2A
G2B
G1
Y7
GND
description
The ′ALS138A and ′AS138 are 3-line to 8-line
decoders/demultiplexers designed for high-
performance memory-decoding or data-routing
applications requiring very short propagation
delay times. In high-performance systems, these
devices can be used to minimize the effects of
system decoding. When employed with
high-speed memories with a fast enable circuit,
thedelaytimesofthedecoderandtheenabletime
of the memory are usually less than the typical
access time of the memory. The effective system
delayintroducedbytheSchottky-clampedsystem
decoder is negligible.
SN54ALS138A, SN54AS138 . . . FK PACKAGE
(TOP VIEW)
3
2
1
20 19
18 Y1
C
G2A
NC
4
5
6
7
8
17
16
15
14
Y2
NC
Y3
Y4
G2B
G1
9 10 11 12 13
The conditions at the binary-select (A, B, and C)
inputs and the three enable (G1, G2A, and G2B)
inputs select one of eight output lines. Two
active-low and one active-high enable inputs
NC – No internal connection
reduce the need for external gates or inverters when expanding. A 24-line decoder can be implemented without
external inverters and a 32-line decoder requires only one inverter. An enable input can be used as a data input
for demultiplexing applications.
The SN54ALS138A and SN54AS138 are characterized for operation over the full military temperature range
of –55°C to 125°C. The SN74ALS138A and SN74AS138 are characterized for operation from 0°C to 70°C.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Copyright 1996, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
1
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