## 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

### Multiple Choice Questions

- A half adder has

- 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. A full adder has

- 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

3. Half adders are used for addition of

- Three bits
- Four bits
- Five bits
- Two bits

**Answer:** Two bits

4. Full adders are used for addition of

- Three bits
- Four bits
- Five bits
- Two bits

**Answer:** Three bits

5. Ripple carry adders use ________ to add two *n*-bit numbers.

- Two half adders
- Two full adders
- One half adder and one full adder
- None of the above

**Answer:** One half adder and one full adder

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

- T
*n*T- 1
- 1–T

**Answer:** *n*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

**Answer:** 4 select input lines

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

- Subtractor
- Decoder
- Multiplexer
- Encoder

**Answer:** 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
- Adders
- Demultiplexer

**Answer:** 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

**Answer:** Decoder

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

**Answer:** both

20. BCD-adder requires — number of full adders

- one
- two
- three
- four

**Answer:** two

21. EX-3 adder requires — number of full adders

- one
- four
- three
- two

**Answer:** two

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

- five
- six
- seven
- eight

**Answer:** seven

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

- one parallel adder
- two parallel adders
- three parallel adders
- four parallel adders

**Answer:** four parallel adders

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

- one
- two
- three
- four

**Answer:** two

26. Magnitude comparator is a circuit that compares

- magnitude of two numbers
- magnitude of three numbers
- magnitude of four numbers
- sign of two numbers

**Answer:** magnitude of two numbers

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

- 2
^{n} - 2
^{n}– 1 - 2
^{n – 1} - 2n

**Answer:** 2^{n}

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

- SOP
- POS
- cannonical SOP
- cannonical POS

**Answer:** cannonical SOP

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

**Answer:** AND-OR

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

- 5
- 6
- 64
- 8

**Answer:** 6

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

**Answer:** All of the above

34. Which of the following statements belongs to a MUX?

- Has more inputs than outputs
- Uses SELECT inputs
- Used in parallel to serial conversion
- All

**Answer:** All