74138 데이터 시트보기 (PDF) - ON Semiconductor
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74138 Datasheet PDF : 8 Pages
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SN74LS138
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 inputs, 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 expansion 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
appropriate active HIGH or active LOW state.
INPUTS
TRUTH TABLE
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
LS04
123
A0 A1 A2
E
LS138
O0 O1 O2 O3 O4 O5 O6 O7
O0
O31
Figure a
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