Page 81 - Computer science 868 Class 12
P. 81
D = A '.A '.A .A ' is 0
2
2
0
1
3
D = A'.A '.A .A is 0
3
0
3
2
1
D = A '.A .A '.A' is 0
2
1
0
3
4
D = A '.A .A '.A is 0
5
2
1
0
3
D = A '.A .A .A ' is 0
6
2
0
3
1
D = A '.A .A .A is 0
3
1
2
0
7
D = A .A '.A '.A ' is 0
0
1
2
3
8
D = A .A '.A '.A is 1
2
0
1
3
9
We conclude output is 1 only across AND gate D which represents decimal 9.
9
Applications of Decoder circuit
1. It is used in the conversion of Binary number to its Octal, Decimal and Hexadecimal form
2. It is used in sequencing signal and timing signal applications
3. It is used in network lines
Drawbacks of Decoder
If the inputs are not connected then the output will not be 0.
Encoder vs Decoder
Encoder Decoder
It converts Octal, Decimal and Hexadecimal to Binary It is used in the conversion of Binary number to its Octal,
Decimal and Hexadecimal from
n
n
It has maximum 2 input lines and n output lines It has n input lines and maximum 2 output lines
Circuit contains OR gate AND and NOT gate used in circuit
2.6 MULTIPLEXER
We have learnt about devices Encoder and Decoder which convert data form one from to another. Now, we will know
how the computer performs selective processing with help of a circuit named a multiplexer.
A Multiplexer is a modified Decoder circuit with additional selection lines and an OR gate. A multiplexer produces one
output from many inputs.
Multiplexer is a combinational circuit which selects a single output from a set of inputs.
n
A multiplexer has 2 input lines and one output line, where n is the number of selection lines.
A Multiplexer also known as MUX can be of the following types:
1. 4 × 1 Multiplexer
2. 8 × 1 Multiplexer
3. 16 × 1 Multiplexer
2.6.1 4 × 1 Multiplexer
A 4x1 Multiplexer has four inputs denoted as A , A , A , and A and two selection lines namely S , S and single output
3
0
1
0
1
2
Y. On the basis of the input combination, only one AND gate will generate output high(1) and is selected while others
have output low(0).
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Computer Hardware 79

