54f138 National Semiconductor Corporation, 54f138 Datasheet - Page 2

• Manufacturer Part Number: 54f138
• Description: 1-of-8 Decoder/demultiplexer
• Manufacturer: National Semiconductor Corporation

Unit Loading Fan Out
Functional Description
The ’F138 high-speed 1-of-8 decoder demultiplexer ac-
cepts three binary weighted inputs (A
enabled provides eight mutually exclusive active LOW out-
puts (O
active LOW (E
will be HIGH unless E
This multiple enable function allows easy parallel expansion
Truth Table
H
L
X
e
Pin Names
A
E
E
O
e
e
E
H
X
X
L
L
L
L
L
L
L
L
0
1
3
0
1
LOW Voltage Level
Immaterial
HIGH Voltage Level
–A
–O
E
2
2
0
7
–O
E
H
X
X
L
L
L
L
L
L
L
L
2
7
) The ’F138 features three Enable inputs two
1
Address Inputs
Enable Inputs (Active LOW)
Enable Input (Active HIGH)
Outputs (Active LOW)
E
E
X
X
H
H
H
H
H
H
H
H
L
2
3
Inputs
) and one active HIGH (E
1
Description
and E
A
H
H
H
H
X
X
X
L
L
L
L
0
2
are LOW and E
A
X
X
X
H
H
H
H
L
L
L
L
1
0
A
A
H
H
H
H
X
X
X
L
L
L
L
1
2
A
3
2
) All outputs
) and when
HIGH LOW
O
3
H
H
H
H
H
H
H
H
H
H
L
0
50 33 3
1 0 1 0
1 0 1 0
1 0 1 0
is HIGH
U L
O
H
H
H
H
H
H
H
H
H
H
L
1
54F 74F
2
O
20 A
20 A
20 A
Output I
H
H
H
H
H
H
H
H
H
H
b
L
2
Input I
1 mA 20 mA
of the device to a 1-of-32 (5 lines to 32 lines) decoder with
just four ’F138 devices and one inverter (See Figure 1 ) The
’F138 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
b
b
b
O
IH
OH
H
H
H
H
H
H
H
H
H
H
Outputs
L
0 6 mA
0 6 mA
0 6 mA
3
I
IL
I
OL
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