74F138PC datasheet(2/10 Pages) NSC

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Unit LoadingFan Out

54F74F

Pin Names

Description

Input IIH IIL

HIGHLOW

Output IOH IOL

A0–A2

Address Inputs

1010

20 mA b06 mA

E1 E2

Enable Inputs (Active LOW)

1010

20 mA b06 mA

Enable Input (Active HIGH)

1010

20 mA b06 mA

O0–O7

Outputs (Active LOW)

50333

1 mA20 mA

Functional Description

The ’F138 high-speed 1-of-8 decoderdemultiplexer ac-

cepts three binary weighted inputs (A0 A1 A2) and when

enabled provides eight mutually exclusive active LOW out-

puts (O0–O7) The ’F138 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 ’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

Truth Table

Inputs

Outputs

HHHHH

HHHH

HHH

HLH

HHH

HHHH

H e HIGH Voltage Level

L e LOW Voltage Level

X e Immaterial

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