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Chapter

74ls138


Department
Electrical Engineering
Course Code
EE 2731
Professor
All

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5-1
FAST AND LS TTL DATA
1-OF-8 DECODER/
DEMULTIPLEXER
The LSTTL/MSI SN54/74LS138 is a high speed 1-of-8 Decoder/
Demultiplexer. This device is ideally suited for high speed bipolar memory
chip select address decoding. The multiple input enables allow parallel ex-
pansion to a 1-of-24 decoder using just three LS138 devices or to a 1-of-32
decoder using four LS138s and one inverter. The LS138 is fabricated with the
Schottky barrier diode process for high speed and is completely compatible
with all Motorola TTL families.
Demultiplexing Capability
Multiple Input Enable for Easy Expansion
Typical Power Dissipation of 32 mW
Active Low Mutually Exclusive Outputs
Input Clamp Diodes Limit High Speed Termination Effects
14 13 12 11 10 9
123456 7
16 15
8
VCC
A0
O0O1O2O3O5
O4O6
A1A2E1E2E3O7GND
CONNECTION DIAGRAM DIP (TOP VIEW)
NOTE:
The Flatpak version
has the same pinouts
(Connection Diagram) as
the Dual In-Line Package.
PIN NAMES LOADING (Note a)
HIGH LOW
A0–A
2
E
1
, E2
E3
O0–O
7
Address Inputs
Enable (Active LOW) Inputs
Enable (Active HIGH) Input
Active LOW Outputs (Note b)
0.5 U.L.
0.5 U.L.
0.5 U.L.
10 U.L.
0.25 U.L.
0.25 U.L.
0.25 U.L.
5 (2.5) U.L.
NOTES:
a) 1 TTL Unit Load (U.L.) = 40 µA HIGH/1.6 mA LOW.
b) The Output LOW drive factor is 2.5 U.L. for Military (54) and 5 U.L. for Commercial (74)
Temperature Ranges.
SN54/74LS138
1-OF-8 DECODER/
DEMULTIPLEXER
LOW POWER SCHOTTKY
J SUFFIX
CERAMIC
CASE 620-09
N SUFFIX
PLASTIC
CASE 648-08
16
1
16
1
ORDERING INFORMATION
SN54LSXXXJ Ceramic
SN74LSXXXN Plastic
SN74LSXXXD SOIC
16
1
D SUFFIX
SOIC
CASE 751B-03
LOGIC SYMBOL
VCC = PIN 16
GND = PIN 8
15 14 13 12 11 10 9
123 456
12 3
A
0A
1A
2E
O
0O
1O
2O
3O
4O
5O
6O
7
7
LOGIC DIAGRAM
A2A1A0E1E2E3
O7O6O5O4O3O2O1O0
VCC = PIN 16
GND = PIN 8
= PIN NUMBERS
3 2 1 4 5 6
7915
14
1312
1110
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