1.If A, B and C are the inputs of a full adder then the carry is given by __________
a) A AND B OR (A OR B) AND C
b) A OR B OR (A AND B) C
c) (A AND B) OR (A AND B)C
d) A XOR B XOR (A XOR B) AND C
Explanation: If A, B and C are the inputs of a full adder then the carry is given by A AND B OR (A OR B) AND C, which is equivalent to (A AND B) OR (B AND C) OR (C AND A).
2. How many AND, OR and EXOR gates are required for the configuration of full adder?
a) 1, 2, 2
b) 2, 1, 2
c) 3, 1, 2
d) 4, 0, 1
Explanation: There are 2 AND, 1 OR and 2 EXOR gates required for the configuration of full adder, provided using half adder. Otherwise, configuration of full adder would require 3 AND, 2 OR and 2 EXOR.
3. Half subtractor is used to perform subtraction of ___________
a) 2 bits
b) 3 bits
c) 4 bits
d) 5 bits
Explanation: Half subtractor is a combinational circuit which is used to perform subtraction of two bits, namely minuend and subtrahend and produces two outputs, borrow and difference.
4. For subtracting 1 from 0, we use to take a _______ from neighbouring bits.
a) Carry
b) Borrow
c) Input
d) Output
Explanation: For subtracting 1 from 0, we use to take a borrow from neighbouring bits because carry is taken into consideration during addition process.
5. How many outputs are required for the implementation of a subtractor?
a) 1
b) 2
c) 3
d) 4
Explanation: There are two outputs required for the implementation of a subtractor. One for the difference and another for borrow.
6. Let the input of a subtractor is A and B then what the output will be if A = B?
a) 0
b) 1
c) A
d) B
Explanation: The output for A = B will be 0. If A = B, it means that A = B = 0 or A = B = 1. In both of the situation subtractor gives 0 as the output.
7. Let A and B is the input of a subtractor then the borrow will be ___________
a) A AND B’
b) A’ AND B
c) A OR B
d) A AND B
Explanation: The borrow of a subtractor is received through AND gate whose one input is inverted. On that basis the borrow will be (A’ AND B).
8. What does minuend and subtrahend denotes in a subtractor?
a) Their corresponding bits of input
b) Its outputs
c) Its inputs
d) Borrow bits
Explanation: Minuend and subtrahend are the two bits of input of a subtractor. If A and B are the two inputs of a subtractor then A is called minuend and B as subtrahend.
9. The full subtractor can be implemented using ___________
a) Two XOR and an OR gates
b) Two half subtractors and an OR gate
c) Two multiplexers and an AND gate
d) Two comparators and an AND gate
Explanation: A full subtractor has 3 input bits and two outputs bits BORROW and DIFFERENCE. The full subtractor can be implemented using two half subtractors and an OR gate.
10.The output of a full subtractor is same as ____________
a) Half adder
b) Full adder
c) Half subtractor
d) Decoder
Explanation: The sum and difference output of a full adder and a full subtractor are same. If A, B and C are the input of a full adder and a full subtractor then the output will be given by (A XOR B XOR C), respectively.