54FCT138 NSC [National Semiconductor], 54FCT138 Datasheet - Page 2

• Manufacturer Part Number: 54FCT138
• Description: 1-of-8 Decoder/Demultiplexer
• Manufacturer: NSC [National Semiconductor]

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Functional Description
The FCT138 high-speed 1-of-8 decoder/demultiplexer ac-
cepts three binary weighted inputs (A
enabled, provides eight mutually exclusive active-LOW out-
puts (O
two active-LOW (E
puts will be HIGH unless E
HIGH. This multiple enable function allows easy parallel ex-
H = HIGH Voltage Level
L = LOW Voltage Level
X = Immaterial
Logic Diagram
Please note that this diagram is provided only for the understanding of logic operations and should not be used to estimate propagation delays.
E
H
X
X
L
L
L
L
L
L
L
L
1
0
–O
E
X
H
X
L
L
L
L
L
L
L
L
2
7
). The FCT138 features three Enable inputs,
E
X
X
H
H
H
H
H
H
H
H
L
Inputs
3
1
, E
2
A
X
X
X
H
H
H
H
) and one active-HIGH (E
L
L
L
L
0
1
A
and E
X
X
X
H
H
H
H
L
L
L
L
1
2
A
X
X
X
H
H
H
H
L
L
L
L
0
2
are LOW and E
, A
1
, A
O
H
H
H
H
H
H
H
H
H
H
L
2
0
) and, when
3
). All out-
O
H
H
H
H
H
H
H
H
H
H
L
1
3
is
O
H
H
H
H
H
H
H
H
H
H
L
2
2
O
Outputs
H
H
H
H
H
H
H
H
H
H
L
pansion of the device to a 1-of-32 (5 lines to 32 lines) de-
coder with just four FCT138 devices and one inverter (see
Figure 1 ). The FCT138 can be used as an 8-output demulti-
plexer by using one of the active LOW Enable inputs as the
data input and the other Enable inputs as strobes. The En-
able inputs which are not used must be permanently tied to
their appropriate active-HIGH or active-LOW state.
3
O
H
H
H
H
H
H
H
H
H
H
L
4
O
H
H
H
H
H
H
H
H
H
H
L
5
O
DS100963-4
H
H
H
H
H
H
H
H
H
H
L
6
O
H
H
H
H
H
H
H
H
H
H
L
7