74AC138_03 FAIRCHILD [Fairchild Semiconductor], 74AC138_03 Datasheet - Page 2

• Manufacturer Part Number: 74AC138_03
• Description: 1-of-8 Decoder/Demultiplexer
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

www.fairchildsemi.com
Truth Table
H
Functional Description
The AC/ACT138 high-speed 1-of-8 decoder/demultiplexer
accepts three binary weighted inputs (A
when enabled, provides eight mutually exclusive active-
LOW outputs (O
Enable inputs, two active-LOW (E
HIGH (E
LOW and E
easy parallel expansion of the device to a 1-of-32 (5 lines
to 32 lines) decoder with just four AC/ACT138 devices and
one inverter (see Figure 1). The AC/ACT138 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.
HIGH Voltage Level
3
). All outputs will be HIGH unless E
3
is HIGH. This multiple enable function allows
E
H
X
X
L
L
L
L
L
L
L
L
1
0
–O
E
7
H
X
X
L
L
L
L
L
L
L
L
). The AC/ACT138 features three
2
L
LOW Voltage Level
E
X
X
H
H
H
H
H
H
H
H
L
Inputs
3
1
A
X
X
X
H
H
H
H
L
L
L
L
, E
0
FIGURE 1. Expansion to 1-of-32 Decoding
2
) and one active-
0
A
H
H
H
H
X
X
X
L
L
L
L
, A
1
1
1
and E
X
, A
A
X
X
X
H
H
H
H
L
L
L
L
Immaterial
2
2
) and,
2
are
O
H
H
H
H
H
H
H
H
H
H
L
0
2
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.
O
H
H
H
H
H
H
H
H
H
H
L
1
O
H
H
H
H
H
H
H
H
H
H
L
2
O
Outputs
H
H
H
H
H
H
H
H
H
H
L
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
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