Mux 2.1

Multiplexers and De-Multiplexers 2:

©Paul GodinUpdated November 2007

Mux 2.2

De-Multiplexers

◊ De-Multiplexers are often used in conjunction with other digital circuits such as decoders, counters and other multi-function devices.

Mux 2.3

A simple De-MUX

X

Y

S

A

Selects whether input “A” goes to “X” or “Y”

Mux 2.4

A Simple De-Multiplexer (2-output)

S

Z

B

A

B

A

If S = 1, value Z is forwarded to AIf S = 0, value Z is forwarded to B

Boolean Expression: A = SZBoolean Expression: B = S’Z

Mux 2.5

A 1-to-4 De-Multiplexer

S0 S1

Z

B

C

D

A

B

A

C

D

Build a function table for this circuit

Mux 2.6

A multi-channel De-MUX

a1

b1

c1

d1

S

A

B

C

Da2

b2

c2

d2

Channel 1

Channel 2

Mux 2.7

Address De-Multiplexer

◊ Microprocessors often multiplex their address bus with their data bus. This is to save on pins and physical size.

◊ At times, address information is on the bus and at other times data is on the bus.

μP

Mux 2.8

Address De-Multiplexer

The Control output from the microprocessor indicates whether the bus

is in Address mode or in Data mode.

ADDRESS

DATA

Control

AD Bus

Mem

ory

μP

Mux 2.9

Questions

◊ What is the difference between a de-multiplexer and an encoder?

Mux 2.10

Questions

◊ Identify the following as MUX or De-MUX

From Texas Instruments, Specification sheet for SN74LS194

Mux 2.11

Questions

◊ Identify the following as MUX or De-MUX

From Texas Instruments, Specification sheet for CD74AC139

Mux 2.12

End

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