Page 100 - Computer science 868 Class 12
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29. What is a half adder? Write the truth table and derive an SOP expression for sum and carry for a half adder. [ISC 2019]
Ans. The half adder is a combinational circuit that is designed to perform the addition of two bits and produce the two binary outputs
as sum (S) and carry (C) bits. If A and B denote two inputs, then sum and carry are:
Input Output
A B Sum Carry
0 0 0 0
0 1 1 0
1 0 1 0
1 1 0 1
30. Draw the logic diagram and truth table for a 2 input XNOR gate. [ISC 2017]
Ans. A B A⊙B A
0 0 1 A⊙B
0 1 0 B
1 0 0
1 1 1 The Boolean expression of the two
variable XNOR gate is A'.B' + A.B.
Truth table of 2 variable XNOR gate
The logic circuit diagram of the two variables XNOR gate is as follows:
A A.B
B
A'.B' + A.B
A'
A'.B'
B'
31. Draw the logic gate diagram for the reduced expression. Assume that the variables and their complements are available as
inputs. [ISC 2017]
Ans.
A A'
A'C
C
A' A'B
B
F
B'
B'C
C
B' AB'D'
D
A D'
32. Draw the logic gate diagram for the reduced expression. Assume that the variables and their complements are available as
inputs. [ISC 2017]
Ans. Logic gate diagram:
A
A'+C'
C
A
A'+D' (A+C)(A+D)(B+D)
D
B
B'+D'
D
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