l7 multiplexers

8/6/2019 L7 Multiplexers

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Multiplexer

It is a combinational logic circuit

Multiplexer is a circuit with many inputs and only one output.

i.e. it accepts several data inputs and allows only one of them

AT A TIME to get through to the output

The routing of desired data input to output is controlled by

SELECT (CONTROL) LINES.

Also called as Data

Selector.

Multiplex meansMany

into one. Multiplexer

m control signals

n i/p signals

1 o/p signal


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Above diagram is of n:1 multiplexer with n input lines, m

control lines and 1 output line. Here2m = n

So we can have

2:1 MUX ;with 1 control line

4:1 MUX ;with 2 control line8:1 MUX ;with 3 control line

16:1 MUX ;with 4 control line


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2:1 Multiplexer

Here the 2: 1 MUX has two I/P lines D0 and D1 and one

select (control) line S0 When S0 =0 then output= D0

When S0 =1 then output= D1

Circuit Diag.

Inputs

OutputS0

0 D0

1 D1


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4:1 Multiplexer

In

puts OutputS1 S0

0 0 D0

0 1 D1

1 0 D2

1 1 D3

Circuit diagram and truth table of 4:1 MUX are shown below:


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Assignment:

Draw circuit diagram and write the truth table of 8:1

Multiplexer and 16:1 multiplexer.


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realizations of a 4-to-1 multiplexer from a decoder, AND

gate and an OR gate:


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Demultiplexer

Also called as Data

distributor.

Demultiplex means one

to Many.

Demultiplexer is a circuit with one input and many outputs.

i.e. it accepts one data input and steer the input signal to one ofthe output line.

The routing of data input to one of the output is controlled by

CONTROL SIGNALS.

The circuit has 1 i/p signal, m control signals & n o/p signals

Demultiplexer

m control signals

1 i/p signals

n o/psignal


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Demultiplexer is exactly reverse of multiplexer.

Above diagram is of 1:n demultiplexer. Relationship b/wm & n is given by

2m = n

where m = no. of control lines, n = no. of output lines

So we can have1:2 DEMUX ;with 1 control line

1:4 DEMUX ;with 2 control line




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1:2 Demultiplexer

Here the 1:2 DEMUX has 2 O/P lines Y0 and Y1 and one

select (control) line S0 When S0 =0 then output= Y0

When S0 =1 then output= Y1

Circuit Diag.


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Inputs Output

S1 S0

0 0 Y0=D

0 1 Y1=D

1 0 Y2=D

1 1 Y3=D

Circuit diagram and truth table of 1:4 DEMUX are shown below:

1:4 Demultiplexer


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Assignment:

Draw circuit diagram and write the truth

table of 1:8 Demultiplexer and 1:16

Demultiplexer.


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Applications

A very common application for this type of circuit is found

in computers, where dynamic memory uses the same

address lines for both row and column addressing. A set of

multiplexers is used to first select the row address to the

memory, then switch to the column address

l7 multiplexers

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