MC74AC138 ON Semiconductor, MC74AC138 Datasheet - Page 2

• Manufacturer Part Number: MC74AC138
• Description: 1-of-8 Decoder / Demultiplexer
• Manufacturer: ON Semiconductor

decoder/demultiplexer accepts three binary weighted inputs
(A 0 , A 1 , A 2 ) and, when enabled, provides eight mutually
exclusive
MC74AC138/74ACT138 features three Enable inputs, two
active–LOW (E 1 , E 2 ) and one active–HIGH (E 3 ). All
outputs will be HIGH unless E 1 and E 2 are LOW and E 3 is
The
MC74AC138/74ACT138
FUNCTIONAL DESCRIPTION
active–LOW
TRUTH TABLE
H = HIGH Voltage Level
L = LOW Voltage Level
X = Immaterial
E 1
H
X
X
L
L
L
L
L
L
L
L
E 2
H
X
X
L
L
L
L
L
L
L
L
E 3
outputs
NOTE:
X
X
H
H
H
H
H
H
H
H
L
Inputs
A 0
X
X
X
H
H
H
H
L
L
L
L
high–speed
This diagram is provided only for the understanding of logic
operations and should not be used to estimate propagation
delays.
(O 0 –O 7 ).
A 1
H
H
H
H
X
X
X
L
L
L
L
MC74AC138, MC74ACT138
Figure 3. Logic Diagram
A 2
X
X
X
H
H
H
H
L
L
L
L
1–of–8
http://onsemi.com
The
O 0
H
H
H
H
H
H
H
H
H
H
L
123
O 1
H
H
H
H
H
H
H
H
H
H
L
HIGH. This multiple enabled function allows easy parallel
expansion of the device to a 1–of–32 (5 lines to 32 lines)
decoder with just four MC74AC138/74ACT138 devices
and
MC74AC138/74ACT138 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.
O 2
H
H
H
H
H
H
H
H
H
H
L
one
O 3
H
H
H
H
H
H
H
H
H
H
Outputs
L
inverter
O 4
H
H
H
H
H
H
H
H
H
H
L
O 5
H
H
H
H
H
H
H
H
H
H
L
(See
O 6
H
H
H
H
H
H
H
H
H
H
L
O 7
H
H
H
H
H
H
H
H
H
H
L
Figure
4).
The