Page 96 - Computer science 868 Class 12
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Decoder is a combinational circuit that converts any binary number to its equivalent Octal, Decimal or Hexadecimal form. It has
n
‘n’ input lines and maximum 2 output lines.
14. Draw the circuit of a two input XOR gate with the help of NOR gates. [ISC 2020]
Ans. XOR gate using only NOR gates: Expression for XOR in POS : F = (A’+B’) • (A+B)
15. Draw the logic gate diagram for the reduced expression. Assume that the variables and their complements are available as
inputs. [ISC 2020]
Ans. Logic gate diagram:
B'
D
A'
D'
B
C'
D'
16. Draw the truth table and derive an SOP expression for sum and carry for a full adder. Also, draw the logic circuit for the carry
of a full adder. [ISC 2020]
Ans. Truth Table for a Full adder:
A B C S C 0
0 0 0 0 0
0 0 1 1 0 A AB
0 1 0 1 0
0 1 1 0 1 B
1 0 0 1 0 B
1 0 1 0 1 BC CARRY
1 1 0 0 1 C
1 1 1 1 1
SOP Expression: C CA
Sum = A'B'C + A'BC' + AB'C' + ABC
Σ(1,2,4,7) A
Carry = A'BC + AB'C + ABC' +ABC
Σ(3,5,6,7)
Circuit for carry: C0 = AB + BC + AC
17. Draw the logic gate diagram for the reduced expression. Assume that the variables and their complements are available as
inputs. [ISC 2018]
Ans. C'
D'
B' F
D'
A
C'
9494 Touchpad Computer Science-XII

