# MCQ on Combinational Logic Circuits

## MCQ on Combinational Logic Circuits

MCQ on Combinational Logic Circuits, Multiple choice questions on combinational logic circuits, MCQ on Half Adder, MCQ on Full Adder, Objective Questions on Combinational logic, MCQ on Look Ahead Carry Adder, Engineering MCQ, Multiple Choice Question based on Engineering, Digital Electronics MCQ

### Multiple Choice Questions

• 2 inputs and 2 outputs
• 2 inputs and 3 outputs
• 3 inputs and 2 outputs
• 3 inputs and 3 outputs

Answer: 2 inputs and 2 outputs

• 2 inputs and 3 outputs
• 2 inputs and 2 outputs
• 3 inputs and 2 outputs
• 3 inputs and 3 outputs

Answer: 2 inputs and 2 outputs

• Three bits
• Four bits
• Five bits
• Two bits

• Three bits
• Four bits
• Five bits
• Two bits

• None of the above

6. An n-bit ripple carry adder having ‘n’ adders has time delay T equal to

• T
• nT
• 1
• 1–T

7. A 1-to-8 demultiplexer has ________ select input lines.

• 2 select input lines
• 3 select input lines
• 8 select input lines
• 4 select input lines

8. The circuit containing 2n input lines and n output lines, that performs converse of decoding is called as

• Subtractor
• Decoder
• Multiplexer
• Encoder

9. In the full adder, if the sum is S and carry is C then

• S = 1 when two or more inputs are unity
• C = 1 when two or more inputs are unity
• S = 1 when all inputs are unity
• C = 1 when all inputs are unity

Answer: C = 1 when two or more inputs are unity

10. The data from input to a selected output line is directed by

• Multiplexer
• Coder
• Demultiplexer

11. A 32 to 1 multiplexer has the following terminals

• 32 outputs, one input and 5 control signals
• 32 inputs, one output and 5 control signals
• 5 inputs, one control signal and 32 outputs
• 5 inputs 32 control signals and one output

Answer: 32 inputs, one output and 5 control signals

12. If a multiplexer can switch one of 16 data inputs to its output then how many inputs does it have?

• 16 data inputs and 1 select inputs
• 8 data inputs and 2 select inputs
• 16 data inputs and 4 select inputs
• 2 data inputs and 8 select inputs

Answer: 16 data inputs and 4 select inputs

13. A half adder circuit is constructed using

• EX-OR gate and NOR gate
• EX-OR gate and OR gate
• EX-OR gate and AND gate
• EX-OR gate and NAND gate

Answer: EX-OR gate and AND gate

14. Demultiplexer is a device used to change

• Sum two parallel data
• Serial data to parallel data
• Parallel data to serial data
• Sum two serial data

Answer: Serial data to parallel data

15. A device that coverts binary words into alphanumeric characters is

• Decoder
• Encoder
• Multiplexer
• Demultiplexer

16. To achieve proper functioning of the encoder, which of the following condition is to be satisfied?

• All inputs are active
• Only one of the inputs is active
• No input is active
• All inputs are at logic 0

Answer: Only one of the inputs is active

17. The addition of two binary variables A and B results into a SUM and CARRY equal to

• Sum = A’B’ + AB, Carry = AB
• Sum = AB + B, carry = A’B
• Sum = AB’ + A’B, Carry = AB
• Sum = AB + A, Carry = A’B’

Answer: Sum = AB’ + A’B, Carry = AB

18. In the half adder circuit given figure if the inputs AB = 10 then

• X = 0; Y = 0
• X = 0; Y = 1
• X = 1; Y = 1
• X = 1; Y = 0

Answer: X = 1; Y = 0

19. In a look ahead carry adder, the carry of each stage (except the initial stage) is a function of

• carry propagate
• carry generate
• both
• none

• one
• two
• three
• four

• one
• four
• three
• two

22. The — number of NAND gates are required to realize a half subtractor

• five
• six
• seven
• eight

23. Full subtractor can be realized by using

• one half-subtractor and one OR gate
• two half-subtractor and one OR gate
• one half-subtractor and one AND gate
• two half-subtractor and one AND gate

Answer: two half-subtractor and one OR gate

24. BCD subtractor requires

25. EX-3 subtractor can be implemented by using — number of parallel adders

• one
• two
• three
• four

26. Magnitude comparator is a circuit that compares

• magnitude of two numbers
• magnitude of three numbers
• magnitude of four numbers
• sign of two numbers

27. A decoder with n inputs produces maximum of — number of minterms

• 2n
• 2n – 1
• 2n – 1
• 2n

28. Any Boolean function can be implemented if it can be represented be — form

• SOP
• POS
• cannonical SOP
• cannonical POS

29. For economical realization decoder is used to realize a function which contains

• less number of don’t cares
• more number of don’t cares
• for any case
• none

Answer: less number of don’t cares

30. A 6-to-64 decoder can be obtained by cascading of…..

• four numbers 4-to-16 decoders and one 2 : 4 decoder
• five numbers 4-to-16 decoders
• three numbers 4-to-16 decoders and two numbers 2 : 4 decoder
• can not possible

Answer: four numbers 4-to-16 decoders and one 2 : 4 decoder

31. MUX is …… implementation

• AND-OR
• OR-AND
• NAND-OR
• NOR-AND

32. What is the number of inputs, outputs of a decoder that accepts 64 different input combinations?

• 5
• 6
• 64
• 8

33. Which of the following statements refers to decoder?

• Only one output can be activated at any time
• Has more outputs than inputs
• Can be used as a BCD to 7 segment display interface
• All of the above