de chapter8 msi logic circuit

8/3/2019 De Chapter8 Msi Logic Circuit

1/15

F O U Z I A H B I N T I M D . Y A S S I N

MSI LOGIC CIRCUIT


2/15

MULTIPLEXER

MUX

1

2

0

3

1

0

A multiplexer (MUX) selects one data line from two or more inputlines and routes data from the selected line to the output. Theparticular data line that is selected is determined by the select inputs.

-Two select (S) lines areshown here to choose any ofthe four data inputs.

- 2n input will need n

selectors.

Dataselect

Datainputs

DataoutputD1

D0

D2D3

S1

S01

0


3/15

4x1 MULTIPLEXER

Truth table for 4x1 mux

Selector o/p

S0 S1 Z

0 0 I00 1 I11 0 I21 1 I3

103102101100 IIII SSSSSSSSZ !

Boolean Expression:

I0

I1

I2

I3

S1 S0

ZMUX 4x1

Block diagram:


4/15

DEMULTIPLEXER

-A demultiplexer (DEMUX) performs the opposite function from a MUX. Itswitches data from one input line to two or more data lines depending on theselect inputs.

- n is a number of selectors that needed to control the data flow.

Dataselectlines

Dataoutputs


5/15

1 x 4 DEMULTIPLEXER

Truth table for 1x4 Demux

Selector Outputs

S0 S1 Q3 Q2 Q1 Q0

0 0 0 0 0 A

0 1 0 0 A 0

1 0 0 A 0 0

1 1 A 0 0 0

AND

S0S1

AND

AND

NOT NOT

AND

A Q0

Q1

Q2

Q3

Q0

Q1

Q2

Q3

A

S0S1

DEMUX 1x4

Block diagram:

)(

)(

)(

)

103

102

10

100

1

(

SSAQ

SSAQ

SSAQ

SSAQ

!

!

!

!

Boolean Expression:


6/15

DECODER

Adecoder is a logic circuit that detects the presence of aspecific combination of bits at its input. Two simple decodersthat detect the presence of the binary code 0011 are shown. Thefirst has an active HIGH output; the second has an active LOW

output.

A1

A0

A2

A3

X

Active HIGH decoder for 0011

A1

A0

A2

A3

X

Active LOW decoder for 0011


7/15

DECODER

IC decoders have multiple outputs to decode any combination ofinputs. For example the binary-to-decimal decoder shown here has 16outputs one for each combination of binary inputs.

Bin/Dec

A0

0

1

2

34

5

6

7

8

9

1011

12

13

14

15

4-bit binary

input

Decimaloutputs

A1

A2

A3

1

1

0

1

1

1

1

1

1

1

1

1

1

101

1

1

1

1


8/15

2 TO 4 DECODER

Truth table for 2 to 4 line decoder

Input Outputs

A B O3 O2 O1 O0

0 0 0 0 0 1

0 1 0 0 1 0

1 0 0 1 0 0

1 1 1 0 0 0

O0

O1

O2

O3

A

BDECODER2TO4

Block diagram:

ABO

BAO

BAO

O BA

!

!

!

!

3

2

0

1Boolean Expression:

AND

AND

AND

AND

NOT

NOT

A

B

O0

O1

O2

O3


9/15

DECODER IMPLEMENTATION

Example:

Given is X (A,B,C) = ABC+ABC+ABC and Y=ABC+ABC. Design a

circuit for a given functions using a decoder and gates.

Solution:

Step 1: Determine the number of outputs, gates and the type of thedecoder.

Number of outputs=2n=8 ; Number of gate= m=2 OR gate.

Type of decoder= 3-to-8 decoder

Step 2: Develop a truth table and draw the circuit

(next slide)


10/15

Truth table for 3-to-8 Decoder

Selector Outputs

A B C X Y

0 0 0 0 1

0 0 1 1 0

0 1 0 0 00 1 1 0 0

1 0 0 1 0

1 0 1 1 0

1 1 0 0 0

1 1 1 0 1

DECODER IMPLEMENTATION

OR

OR

Decoder 3-to-8

A

B

C

O0

O1

O2

O3

O4

O5

O6

O7

Y

X


11/15

BCD DECODER/DRIVER

The a-g outputs are designedfor much higher current thanmost devices (hence the worddriver in the name).

a

b

c

d

ef

g

1

2

4

8

(16)

(4)

(13)

(12)

(11)

(10)

(9)

(15)

(14)

(1)

(2)

(6)

(7)

(3)

(5)

(8)

BCDinputs

Outputsto sevensegment

device

GND

VCC

BI/RBO

LT

RBI

Another useful decoder is the 74LS47. This is a BCD-to-seven segmentdisplay with active LOW outputs.


12/15

BCD-TO-7 SEGMENT DISPLAY

The7446/47

activatesspecific

segment patterns

inresponse toinput codes

Digital Systems: Principles and Applications, 11/eRonald J. Tocci, NealS. Widmer, Gregory L. Moss

Bycontrollingcurrent

througheach LED,

somesegments are

turnedon & emit light,

whileothers are

turnedoff, which

generates thedesired

characterpattern.


13/15

74LS138 DECODER 3-to-8

Digital Systems: Principles and Applications, 11/eRonald J. Tocci, NealS. Widmer, Gregory L. Moss


14/15

ENCODER

An encoderaccepts an active logic level on one of its inputs andconverts it to a coded output, such as BCD or binary.

The decimal to BCD is an encoderwith an input for each of the tendecimal digits and four outputsthat represent the BCD code forthe active digit. The basic logicdiagram is shown. There is nozero input because the outputs areall LOW when the input is zero.

A1

A0

A2

A3

1

2

3

456

8

9


15/15

4-TO-2 ENCODER

Truth table for 4-to-2 Encoder

INPUT OUTPUT

A3 A2 A1 A0 O1 O0

0 0 0 1 0 0

0 0 1 0 0 1

0 1 0 0 1 01 0 0 0 1 1

OR

OR

A0

A1

A2

A3

O1

O0

32

310

1 AAO

AO A

!

!Boolean Expression:

A0

A1

A2

A3

O0

O1

4-to2 Encoder

Block diagram:

de chapter8 msi logic circuit

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