© 2000 Fairchild Semiconductor Corporation DS006111 www.fairchildsemi.com
September 1986
Revised February 2000
DM74ALS138 3 to 8 Line Decoder/Demultiplexer
DM74ALS138
3 to 8 Line 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 DM74ALS138 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 32-line decoder
requires only one inverter. An enable input can be used as
a data input for demultiplexing applications.
This decoder/demultiplexer features 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 system design.
Features
■ Designed specifically for high speed:
Memory decoders
Data transmission systems
■ 3- to 8-line decoder incorporates 3 enable inputs to sim-
plify cascading and/or data reception
■ Low power dissipation…23 mW typ
■ Switching specifications guaranteed over full tempera-
ture and V
CC
range
■ Advanced oxide-isolated, ion-implanted Schottky TTL
process
Ordering Code:
Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
Connection Diagram Function Table
Note 1: G2 = G2A + G2B
Order Number Package Number Package Description
DM74ALS138M M16A 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
DM74ALS138SJ M16D 16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
DM74ALS138N N16E 16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
Enable Select
Outputs
Inputs Inputs
G1 G
2
(Note 1)
C B A Y0Y1Y2Y3Y4Y5Y6Y7
X H XXXHHHHHHHH
L X XXXHHHHHHHH
H L LL LLHHHHHHH
H L LLHHLHHHHHH
H L LHLHHLHHHHH
H L LHHHHHLHHHH
H L HLLHHHHLHHH
H L HLHHHHHHLHH
H L HHLHHHHHHLH
H L HHHHHHHHHHL
