Functional Description

The ’AC/’ACT138 high-speed 1-of-8 decoder/demultiplexer

accepts three binary weighted inputs (A

enabled, provides eight mutually exclusive active-LOW out-

puts (O

puts, two active-LOW (E

outputs will be HIGH unless E

HIGH. This multiple enable function allows easy parallel ex-

pansion of the device to a 1-of-32 (5 lines to 32 lines) de-

coder 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.

Truth Table

Inputs

Outputs

E

1

E

2

E

3

A

0

A

1

A

2

O

0

O

1

O

2

O

3

O

4

O

5

O

6

O

7

H

XXXXX

HHHHHHHH

X

H

XXXX

HHHHHHHH

X

X

L

X

X

X

HHHHHHHH

LL

H

LLLL

HHHHHHH

L

L

HH

L

L

H

L

HHHHHH

L

L

H

L

H

L

HH

L

HHHHH

L

L

HHH

L

HHH

L

HHHH

L

L

H

L

L

HHHHH

L

HHH

L

L

HH

L

HHHHHH

L

H

H

L

L

H

L

HHHHHHHH

L

H

L

L

HHHHHHHHHHH

L

H = HIGH Voltage Level

L = LOW Voltage Level

X = Immaterial

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