SN74LS138N データシートの表示（PDF） - Motorola => Freescale
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SN74LS138N Datasheet PDF : 5 Pages
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SN54 / 74LS138
FUNCTIONAL DESCRIPTION
The LS138 is a high speed 1-of-8 Decoder/Demultiplexer
fabricated with the low power Schottky barrier diode process.
The decoder accepts three binary weighted inputs (A0, A1, A2)
and when enabled provides eight mutually exclusive active
LOW Outputs (O0 – O7). The LS138 features three Enable in-
puts, two active LOW (E1, E2) and one active HIGH (E3). All
outputs will be HIGH unless E1 and E2 are LOW and E3 is
HIGH. This multiple enable function allows easy parallel ex-
pansion of the device to a 1-of-32 (5 lines to 32 lines) decoder
with just four LS138s and one inverter. (See Figure a.)
The LS138 can be used as an 8-output demultiplexer by
using one of the active LOW Enable inputs as the data input
and the other Enable inputs as strobes. The Enable inputs
which are not used must be permanently tied to their appropri-
ate active HIGH or active LOW state.
TRUTH TABLE
INPUTS
OUTPUTS
E1
E2
E3
A0
A1
A2
O0
O1
O2
O3
O4
O5
O6
O7
H
X
X
X
X
X
H
H
H
H
H
H
H
H
X
H
X
X
X
X
H
H
H
H
H
H
H
H
X
X
L
X
X
X
H
H
H
H
H
H
H
H
L
L
H
L
L
L
L
H
H
H
H
H
H
H
L
L
H
H
L
L
H
L
H
H
H
H
H
H
L
L
H
L
H
L
H
H
L
H
H
H
H
H
L
L
H
H
H
L
H
H
H
L
H
H
H
H
L
L
H
L
L
H
H
H
H
H
L
H
H
H
L
L
H
H
L
H
H
H
H
H
H
L
H
H
L
L
H
L
H
H
H
H
H
H
H
H
L
H
L
L
H
H
H
H
H
H
H
H
H
H
H
L
H = HIGH Voltage Level
L = LOW Voltage Level
X = Don’t Care
A0
A1
A2
A3
A4
H
123
A0 A1 A2
E
LS138
O0 O1 O2 O3 O4 O5 O6 O7
123
A0 A1 A2
E
LS138
O0 O1 O2 O3 O4 O5 O6 O7
123
A0 A1 A2
E
LS138
O0 O1 O2 O3 O4 O5 O6 O7
O0
Figure a
LS04
123
A0 A1 A2
E
LS138
O0 O1 O2 O3 O4 O5 O6 O7
O31
FAST AND LS TTL DATA
5-231
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