Texas Instruments 85504012A, 8550401FA Datasheet
SN54HCT138, SN74HCT138
3-LINE TO 8-LINE DECODERS/DEMULTIPLEXERS
SCLS171C – MARCH 1984 – REVISED MA Y 1997
1
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
D
Inputs Are TTL-Voltage Compatible
D
Designed Specifically for High-Speed
Memory Decoders and Data Transmission
Systems
D
Incorporate Three Enable Inputs to Simplify
Cascading and/or Data Reception
D
Package Options Include Plastic
Small-Outline (D), Thin Shrink
Small-Outline (PW), and Ceramic Flat (W)
Packages, Ceramic Chip Carriers (FK), and
Standard Plastic (N) and Ceramic (J)
300-mil DIPs
description
The ’HCT138 are designed for high-performance
memory-decoding or data-routing applications
requiring very short propagation delay times. In
high-performance memory systems, these
decoders can minimize the effects of system
decoding. When employed with high-speed
memories utilizing a fast enable circuit, the delay
times of these decoders and the enable time of the
memory are usually less than the typical access
time of the memory . This means that the effective
system delay introduced by the decoders is
negligible.
The conditions at the binary-select inputs and the three enable inputs select one of eight output lines. Two
active-low (G
) and one active-high (G) enable inputs 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 SN54HCT138 is characterized for operation over the full military temperature range of –55°C to 125°C. The
SN74HCT138 is characterized for operation from –40°C to 85°C.
3212019
910111213
4
5
6
7
8
18
17
16
15
14
Y1
Y2
NC
Y3
Y4
C
G
2A
NC
G
2B
G1
BANC
Y6
Y5
V
Y0
Y7
GND
NC
SN54HCT138 ...FK PACKAGE
(TOP VIEW)
CC
NC – No internal connection
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
A
B
C
G
2A
G
2B
G1
Y7
GND
V
CC
Y0
Y1
Y2
Y3
Y4
Y5
Y6
SN54HCT138 ...J OR W PACKAGE
SN74HCT138 . . . D, N, OR PW PACKAGE
(TOP VIEW)
Copyright 1997, Texas Instruments Incorporated
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.
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.
SN54HCT138, SN74HCT138
3-LINE TO 8-LINE DECODERS/DEMULTIPLEXERS
SCLS171C – MARCH 1984 – REVISED MA Y 1997
2
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
FUNCTION TABLE
INPUTS
ENABLE SELECT
OUTPUTS
G1 G2A G2B C B A Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7
X H X X X X H H H H H H H H
X XHXXXHHHHHHHH
L XXXXXHHHHHHHH
H LLLLLLHHHHHHH
H LLLLHHLHHHHHH
H LLLHLHHLHHHHH
H LLLHHHHHLHHHH
H LLHLLHHHHLHHH
H LLHLHHHHHHLHH
H LLHHLHHHHHHLH
H L L H H H H H H H H H H L
logic symbols (alternatives)
†
1
1
A
Y0
15
0
2
2
B
4
3
C
Y1
14
1
Y2
13
2
Y3
12
3
Y4
11
4
Y5
10
5
Y6
9
6
Y7
7
7
BIN/OCT
6
4
5
G1
G2A
G
2B
&
EN
0
1
A
Y0
15
0
2
B
2
3
C
Y1
14
1
Y2
13
2
Y3
12
3
Y4
11
4
Y5
10
5
Y6
9
6
Y7
7
7
DMUX
6
4
5
G1
G2A
G
2B
&
G
0
7
†
These symbols are in accordance with ANSI/IEEE Std 91-1984 and IEC Publication 617-12.
Pin numbers shown are for the D, J, N, PW, and W packages.
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