Encoder, Decoder, Multiplexor, De-multiplexor

Name ID

Muhammad Numan Yousaf 13003065009

Qasim Shehzad 13003065028

Waqar-ul-Malik 13003065050

Seharyar Munir 13003065049

Haseeb-ur-Rehman 13003065034

Multiplexer and De-Multiplexer

• A multiplexer is a circuit that accept many input but giveonly one output. A de-multiplexer function exactly in thereverse of a multiplexer, that is a de-multiplexer acceptsonly one input and gives many outputs. Generallymultiplexer and de-multiplexer are used together, becauseof the communication systems are bi directional.

Multiplexer

Multiplexer means manyinto one. A multiplexer is acircuit used to select androute any one of the severalinput signals to a signaloutput. An simple exampleof an non electronic circuitof a multiplexer is a singlepole multi position switch.

Single Pole Multi Position Switch

Uses of Multiplexers

Multi-position switches arewidely used in manyelectronics circuits. Howevercircuits that operate at highspeed require the multiplexerto be automatically selected. Amechanical switch cannotperform this task satisfactorily.Therefore, multiplexer used toperform high speed switchingare constructed of electroniccomponents. Multiplexer

Types of Multiplexer

• Multiplexer handle two type of data that is analogand digital. For analog application, multiplexerare built of relays and transistor switches. Fordigital application, they are built from standardlogic gates.

• The multiplexer used for digital applications, alsocalled digital multiplexer, is a circuit with manyinput but only one output. By applying controlsignals, we can steer any input to the output. Fewtypes of multiplexer are 2-to-1, 4-to-1, 8-to-1, 16-to-1 multiplexer.

4-to-1 Multiplexer

The 4-to-1 multiplexer has 4 input bit, 2 control bits, and 1 output bit. The four input bits are I0,I1,I2 and I3. only one of this is transmitted to the output y. The output depends on the value of S0 and S1 which is the control input. The control input determines which of the input data bit is transmitted to the output.

4-to-1 multiplexer

4-to-1 Multiplexer

S1 S0 F

0 0 I0

0 1 I1

1 0 I2

1 1 I3

4-to-1 Multiplexer

• An example of 4-to-1 multiplexer is IC 74153 in which the output is same as the input.

• Another example of 4-to-1 multiplexer is 45352 in which the output is the compliment of the input.

• Example of 16-to-1 line multiplexer is IC74150.

Applications of Multiplexer

• Multiplexer are used in various fields where multiple data need to be transmitted using a single line. Following are some of the applications of multiplexers

• Communication system

• Telephone network

• Computer memory

• Transmission from the computer system of a satellite

De-multiplexer

De-multiplexer means one tomany. A de-multiplexer is acircuit with one input andmany output. By applyingcontrol signal, we can steerany input to the output. Fewtypes of de-multiplexer are 1-to 2, 1-to-4, 1-to-8 and 1-to16 de-multiplexer 1-to-4

De- multiplexer

1-to-4 De-Multiplexer

A B Y0 Y1 Y2 Y3

0 0 I 0 0 0

0 1 0 I 0 0

1 0 0 0 I 0

1 1 0 0 0 I

Applications of De-Multiplexer

• De-multiplexer is used to connect a single source to multiple destinations. The main application area of de-multiplexer is communication system where multiplexer are used.

• Communication System

• ALU (Arithmetic Logic Unit)

• Serial to parallel converter

Decoders

A decoder has N inputs

2N outputs

A decoder selects one of 2N outputs by decoding the binary value on the N inputs.

The decoder generates all of the min-terms of the N input variables.

Exactly one output will be active for each combination of the inputs.

Decoders

•A decoder is a logic circuit that accepts a set of inputs that

represents a binary number and activates only the output that

corresponds to the input number.

•In other words, a decoder circuit looks at its inputs,

determines which binary number is present there, and activates

the one output that corresponds to that number ; all other

outputs remain inactive

General decoder diagram

# There are 2N possible input combinations, from A0 to AN1.

For each of these input combinations only one of the M outputs will be activeHIGH (1), all the other outputs are LOW (0).

Decoders

A B W X Y Z

0 0 1 0 0 0

0 1 0 1 0 0

1 0 0 0 1 0

1 1 0 0 0 1

Active-high outputs

BW

X

Y

Z

I0

I1A

Out0

Out1

Out2

Out3

W = A'.B'

X = A.B'

Y = A'.B

Z = A.Bmsb

2-to-4 Decoder

• A 2-to-4 Decoder▫ 2 inputs (A1, A0)

▫ 22 = 4 outputs (D3, D2, D1, D0)

▫ Truth Table

A1 A0 D0 D1 D2 D3

0 0 1 0 0 0

0 1 0 1 0 0

1 0 0 0 1 0

1 1 0 0 0 1

2-to-4 Decoder with Enable

EN

A1 A0 D0 D1 D2 D3

0 X X 0 0 0 0

1 0 0 1 0 0 0

1 0 1 0 1 0 0

1 1 0 0 0 1 0

1 1 1 0 0 0 1

Truth Table

3-to-8 Decoder

A2

A1 A0

D0

D1

D2

D3

D4

D5

D6

D7

0 0 0 1 0 0 0 0 0 0 0

0 0 1 0 1 0 0 0 0 0 0

0 1 0 0 0 1 0 0 0 0 0

0 1 1 0 0 0 1 0 0 0 0

1 0 0 0 0 0 0 1 0 0 0

1 0 1 0 0 0 0 0 1 0 0

1 1 0 0 0 0 0 0 0 1 0

1 1 1 0 0 0 0 0 0 0 1

3-to-8 Decoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

3-to-8 Decoder

3-to-8 Decoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

Decodersmsb

Encoders An encoder has

2N inputs

N outputs

An encoder outputs the binary value of the selected (or active) input.

An encoder performs the inverse operation of a decoder.

Issues What if more than one input is active?

What if no inputs are active?

Encoders

A B C D Y Z

0 0 0 1 0 0

0 0 1 0 0 1

0 1 0 0 1 0

1 0 0 0 1 1

D

Z

Y

I0

I1C

B I2

I3A

Out0

Out1

Priority Encoders

If more than one input is active, the higher-order input has priority over the lower-order input.

The higher value is encoded on the output

A valid indicator, d, is included to indicate whether or not the output is valid.

Output is invalid when no inputs are active

d = 0

Output is valid when at least one input is active

d = 1

8-to-3 Encoder (truth table)

8-to-3

Encoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

inputs outputs

D7 D6

D5 D4

D3

D2

D1 D0

A2 A1 A0

0 0 0 0 0 0 0 1 0 0 0

0 0 0 0 0 0 1 0 0 0 1

0 0 0 0 0 1 0 0 0 1 0

0 0 0 0 1 0 0 0 0 1 1

0 0 0 1 0 0 0 0 1 0 0

0 0 1 0 0 0 0 0 1 0 1

0 1 0 0 0 0 0 0 1 1 0

1 0 0 0 0 0 0 0 1 1 1

8-to-3 Encoder (truth table)

8-to-3

Encoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

10000000

000

inputs outputs

D7 D6

D5 D4

D3

D2

D1 D0

A2 A1 A0

0 0 0 0 0 0 0 1 0 0 0

0 0 0 0 0 0 1 0 0 0 1

0 0 0 0 0 1 0 0 0 1 0

0 0 0 0 1 0 0 0 0 1 1

0 0 0 1 0 0 0 0 1 0 0

0 0 1 0 0 0 0 0 1 0 1

0 1 0 0 0 0 0 0 1 1 0

1 0 0 0 0 0 0 0 1 1 1

8-to-3 Encoder (truth table)

8-to-3

Encoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

01000000

100

inputs outputs

D7 D6

D5 D4

D3

D2

D1 D0

A2 A1 A0

0 0 0 0 0 0 0 1 0 0 0

0 0 0 0 0 0 1 0 0 0 1

0 0 0 0 0 1 0 0 0 1 0

0 0 0 0 1 0 0 0 0 1 1

0 0 0 1 0 0 0 0 1 0 0

0 0 1 0 0 0 0 0 1 0 1

0 1 0 0 0 0 0 0 1 1 0

1 0 0 0 0 0 0 0 1 1 1

8-to-3 Encoder (truth table)

8-to-3

Encoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

00000100

101

inputs outputs

D7 D6

D5 D4

D3

D2

D1 D0

A2 A1 A0

0 0 0 0 0 0 0 1 0 0 0

0 0 0 0 0 0 1 0 0 0 1

0 0 0 0 0 1 0 0 0 1 0

0 0 0 0 1 0 0 0 0 1 1

0 0 0 1 0 0 0 0 1 0 0

0 0 1 0 0 0 0 0 1 0 1

0 1 0 0 0 0 0 0 1 1 0

1 0 0 0 0 0 0 0 1 1 1

8-to-3 Encoder (truth table)

8-to-3

Encoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

00000001

111

inputs outputs

D7 D6

D5 D4

D3

D2

D1 D0

A2 A1 A0

0 0 0 0 0 0 0 1 0 0 0

0 0 0 0 0 0 1 0 0 0 1

0 0 0 0 0 1 0 0 0 1 0

0 0 0 0 1 0 0 0 0 1 1

0 0 0 1 0 0 0 0 1 0 0

0 0 1 0 0 0 0 0 1 0 1

0 1 0 0 0 0 0 0 1 1 0

1 0 0 0 0 0 0 0 1 1 1

8-to-3 Encoder (equations)

8-to-3

Encoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

inputs outputs

D7 D6

D5 D4

D3

D2

D1 D0

A2 A1 A0

0 0 0 0 0 0 0 1 0 0 0

0 0 0 0 0 0 1 0 0 0 1

0 0 0 0 0 1 0 0 0 1 0

0 0 0 0 1 0 0 0 0 1 1

0 0 0 1 0 0 0 0 1 0 0

0 0 1 0 0 0 0 0 1 0 1

0 1 0 0 0 0 0 0 1 1 0

1 0 0 0 0 0 0 0 1 1 1

Note: This truth table is not complete! Why?

Output equations:

A0 = ?A1 = ?A2 = ?

8-to-3 Encoder (equations)

8-to-3

Encoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

inputs outputs

D7 D6

D5 D4

D3

D2

D1 D0

A2 A1 A0

0 0 0 0 0 0 0 1 0 0 0

0 0 0 0 0 0 1 0 0 0 1

0 0 0 0 0 1 0 0 0 1 0

0 0 0 0 1 0 0 0 0 1 1

0 0 0 1 0 0 0 0 1 0 0

0 0 1 0 0 0 0 0 1 0 1

0 1 0 0 0 0 0 0 1 1 0

1 0 0 0 0 0 0 0 1 1 1

Output equations:

A0 = D1 + D3 + D5 + D7

A1 = ?A2 = ?

8-to-3 Encoder (equations)

8-to-3

Encoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

inputs outputs

D7 D6

D5 D4

D3

D2

D1 D0

A2 A1 A0

0 0 0 0 0 0 0 1 0 0 0

0 0 0 0 0 0 1 0 0 0 1

0 0 0 0 0 1 0 0 0 1 0

0 0 0 0 1 0 0 0 0 1 1

0 0 0 1 0 0 0 0 1 0 0

0 0 1 0 0 0 0 0 1 0 1

0 1 0 0 0 0 0 0 1 1 0

1 0 0 0 0 0 0 0 1 1 1

Output equations:

A0 = D1 + D3 + D5 + D7

A1 = D2 + D3 + D6 + D7

A2 = ?

8-to-3 Encoder (equations)

8-to-3

Encoder

D0

D1

D2

D3

D4

D5

D6

D7

A0

A1

A2

inputs outputs

D7 D6

D5 D4

D3

D2

D1 D0

A2 A1 A0

0 0 0 0 0 0 0 1 0 0 0

0 0 0 0 0 0 1 0 0 0 1

0 0 0 0 0 1 0 0 0 1 0

0 0 0 0 1 0 0 0 0 1 1

0 0 0 1 0 0 0 0 1 0 0

0 0 1 0 0 0 0 0 1 0 1

0 1 0 0 0 0 0 0 1 1 0

1 0 0 0 0 0 0 0 1 1 1

Output equations:

A0 = D1 + D3 + D5 + D7

A1 = D2 + D3 + D6 + D7

A2 = D4 + D5 + D6 + D7