DM74S138 鈥?DM74S139 Decoder/Demultiplexer
August 1986
Revised April 2000
DM74S138 鈥?DM74S139
Decoder/Demultiplexer
General Description
These Schottky-clamped circuits are designed to be used
in high-performance memory-decoding or data-routing
applications, requiring very short propagation delay times.
In high-performance memory systems these decoders can
be used to minimize the effects of system decoding. When
used with high-speed memories, the delay times of these
decoders are usually less than the typical access time of
the memory. This means that the effective system delay
introduced by the decoder is negligible.
The DM74S138 decodes one-of-eight lines, based upon
the conditions at the three binary select inputs and the
three enable inputs. Two active-LOW and one active-HIGH
enable inputs reduce the need for external gates or invert-
ers when expanding. A 24-line decoder can be imple-
mented with no 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 DM74S139 comprises two separate two-line-to-four-
line decoders in a single package. The active-LOW enable
input can be used as a data line in demultiplexing applica-
tions.
All of these decoders/demultiplexers feature fully buffered
inputs, presenting only one normalized load to its driving
circuit. All inputs are clamped with high-performance
Schottky diodes to suppress line-ringing and simplify sys-
tem design.
Features
s
Designed specifically for high speed:
Memory decoders
Data transmission systems
s
DM74S138 3-to-8-line decoders incorporates 3 enable
inputs to simplify cascading and/or data reception
s
DM74S139 contains two fully independent 2-to-4-line
decoders/demultiplexers
s
Schottky clamped for high performance
s
Typical propagation delay time (3 levels of logic)
DM74S138 8 ns
DM74S139 7.5 ns
s
Typical power dissipation
DM74S138 245 mW
DM74S139 300 mW
Ordering Code:
Order Number
DM74S138N
DM74S139N
Package Number
N16E
N16E
Package Description
16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
漏 2000 Fairchild Semiconductor Corporation
DS006466
www.fairchildsemi.com
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