Mux 1.1

Multiplexers and De-Multiplexers 1

©Paul GodinUpdated Sept 2009

Mux 1.2

Definitions

◊ Multiplexer:◊ A device that selectively forwards a single source of

data from multiple sources.◊ Often called a MUX.

Input Signals

Output signal

Selection

Mux 1.3

Definitions

◊ De-Multiplexer:◊ A device that forwards an input signal to a selected

output.◊ Often called a DEMUX.

Input Signal

Output signal

Selection

Mux 1.4

Multiplexer – Selected input to single output

A

B

C

D

Output

Rotary selector switch

A

B

C

D

S0 S1

Y

Mechanical Equivalent

Logic Diagram

Mux 1.5

De-multiplexer – Single input to selected output

A

B

C

D

Input

Rotary selector switch

A

B

C

D

S0

S1

Y

Mechanical Equivalent

Logic Diagram

Mux 1.6

MUX and DEMUX Combination

◊ A mechanical combination MUX and DEMUX is often used when evaluating stereo equipment in a store.

Unit #1

Unit #2

Unit #3

Unit #4

Speakers #1

Speakers #2

Speakers #3

Speakers #4Selector(MUX)

Selector(DEMUX)

Direction of data

Mux 1.7

MUX and DEMUX Combination

◊ A combination MUX and DEMUX is used in data communications.

Mux 1.8

Multiplexers

Mux 1.9

Examples of Multiplexers

◊ Examples of selectively forwarding an input signal to an output includes:◊ Selection switch on a home stereo, where one selects

between several sources to be sent to the amplifier and speakers.

◊ A multi-line telephone where one line is selected.◊ A video surveillance monitor that switches between

cameras.

◊ Multiplexers are used extensively in data and voice communication networks

Mux 1.10

Multiplexers

◊ Digital applications for multiplexers include external and internal applications (steering gates).

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

Mux 1.11

A Simple Multiplexer (2-input)

SZ

BA

A

B

If S = 0, value A is forwardedIf S = 1, value B is forwarded

Boolean Expression: Z = S’A + SB

Mux 1.12

A 4-to-1 Multiplexer

S0 S1

ZB

C

D

A

B

A

C

D

Mux 1.13

A 4-to-1 Multiplexer with Enable

What is the Boolean Expression for this circuit?

Build a function table for this circuit

S0 S1

ZB

A

C

D

B

C

D

A

En’

Mux 1.14

A multi-channel MUX

A1

B1

C1

D1

S

a

b

c

dA2

B2

C2

D2

Channel 1

Channel 2

En

Mux 1.15

Multi-Channel MUX in a Digital Alarm Clock

Alarm / Real Time

Decoder Decoder Decoder Decoder

Digital ClockReal Time

Digital ClockAlarm Time

VAM

PM

13 bits

13 bitsThe MUX permits the

sharing of the displays and the decoders.

Mux 1.16

A 7-Segment Display for Multiplexing

cb

a

d

e

fg

Common: Digit 1

Common: Digit 2 cb

ad

ef

g

Common: Digit 1 Common: Digit 2

To display a digit enable the common for that digit only.

Mux 1.17

Multi-Channel MUX in a Shared Display

Oscillator

Decoder

1’s counter

With a high enough frequency, the digits appear to both be lit at the same time.

10’s counter

Oscillator

Select

Mux 1.18

4-to-1 MUX in a Basic Frequency Selector

÷2

The MUX selects the output frequency.

÷2

÷4

÷1000

Output

4kHz

1kHz

500Hz

250Hz

Binary Value

4MHz Crystal

S0 S1

Mux 1.19

Questions

◊ What is the difference between a multiplexer and a decoder?

Mux 1.20

End

prgodin @ gmail.com