theory lecture 14

7/27/2019 Theory Lecture 14

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MCT-212: DIGITAL LOGIC

DESIGN


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MULTIPLEXERS

A multiplexer(MUX) selects one data line from two or moreinput lines and routes data from the selected line to the

output.

0

1

23

DataInputs

0

1

Data

Select

MUX

Data

Output

The particular data

line that is selected isdetermined by the

select inputs.

Multiplexers are also

known as DataSelectors.


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4-INPUT MULTIPLEXER

Can select the data from four lines depending on thecombination of two select bits.

0

1

23

Data

Inputs

0

1

Data

Select

MUX

Data

Output

Data Select InputSelected

1 0

0 0

0 1

1 0

1 1

= 1

0

0

+ 1

0

1

+ 1

0

2

+ 1

2

3


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4-INPUT MULTIPLEXER

Data Select Input

Selected1 0

0 0

0 1

1 0

1 1


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EXPANDED MULTIPLEXERS

The enable (EN) pin disables the outputs of the MUX.

This way the MUX can be used one at a time.


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MULTIPLEXERS AND LOGIC

FUNCTIONS

A useful application of the MUX is in the generationof combinational logic functions in sum-of-

products form.

So whats the use [o_0]?Can replace discrete logic gates.

Often greatly reduces the

number of ICs.

Can make design changes much

easier


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MULTIPLEXERS AND LOGIC

FUNCTIONS

Consider 74LS151, an 8-input MUX, that can beuse to implement any 3-variable logic function.

The variables are connected to the data-select

inputs, and each data-input is set to logic levelrequired in the truth table of the function to be

implemented.

Example: Implement the following logic function:

F (A,B,C) = (3,5,6,7)


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Example: Implement the following logic function:

F (A,B,C) = (3,5,6,7) A B C f(A,B,C)

0 0 0 0

0 0 1 0

0 1 0 0

0 1 1 1

1 0 0 01 0 1 1

1 1 0 1

1 1 1 1

0

1

2

34

5

6

7

Func.

Inputs

0

1

2

Input

Variables

MUX Data

Output

+5

= + +

+


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DEMULTIPLEXERSThe opposite of MUX

MUX

DEM

UX

Meanwhile, in digital communication land.


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DEMULTIPLEXERS

A demultiplexer (DEMUX) performs the opposite functionfrom a MUX. It switches data from one input line to two or

more data lines depending on the select inputs.

0

1

23

DataInput

0

1

Data

Select

DEMUX

Data

Output

Lines

Data Select OutputSelected

1 0

0 0

0 1

1 0

1 1


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DEMULTIPLEXERS

Data Select OutputSelected

1 0

0 0

0 1

1 0

1 1


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You will use and enhance the following skills:

Project Design Analysis

PCB Design

Soldering

Datasheet Reading

Having fun..!!_\m/

Durat

ion:3-4Weeks

Are you willing tovolunteer?


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ANY QUESTIONS?

Anyone willing to present?

Time allowed : 5 mins

Topic : Any Bonus Points : +3


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REFERENCES

Chapter no 5: MSI and PLD components Digi tal Lo gic Designby Morris Mano

Chapter no 6: Functions of Combination Logic

Digi tal Fundamentalsby Floyd

theory lecture 14

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