# Digital Circuits Multiple-Choice Questions (MCQs)

**Digital circuits** is a field of electronics involving the study of digital signals and the engineering of devices that use or produce them.

**Digital Circuits MCQs**: This section contains multiple-choice questions and answers on the various topics of Digital Circuits. Practice these MCQs to test and enhance your skills on Digital Circuits.

## List of Digital Circuits MCQs

**1. What is the base of the decimal number system?**

- 2
- 8
- 10
- 16

**Answer:** C) 10

**Explanation:**

The base of the decimal number system is 10.

**2. What is the range of the decimal number system?**

- 1-10
- 0-10
- 0-9

**Answer:** C) 0-9

**Explanation:**

The range of the decimal number system is 10.

**3. Integer part is the part that lies to the ____ of the decimal point in the Decimal number system.**

- Right
- Left

**Answer:** B) Left

**Explanation:**

The integer part is the part that lies to the left of the decimal point in the Decimal number system.

**4. The ____ component is the part of the number to the right of the decimal point.**

- Fractional
- Integer

**Answer:** A) Fractional

**Explanation:**

The Fractional component is the part of the number to the right of the decimal point.

**5. What of the following is the correct representation of a decimal number system?**

- 192.146 = (1 × 10
^{2}) + (9 × 10^{1}) + (2 × 10^{0}) + (1 × 10^{-1}) + (4 × 10^{-2}) + (6 × 10^{-3}) - 192.146 = (1 × 10
^{3}) + (9 × 10^{2}) + (2 × 10^{1}) + (1 × 10^{-1}) + (4 × 10^{-2}) + (6 × 10^{-3}) - 192.146 = (1 × 10
^{1}) + (9 × 10^{2}) + (2 × 10^{3}) + (1 × 10^{-1}) + (4 × 10^{-2}) + (6 × 10^{-3}) - None

**Answer:** A) 192.146 = (1 × 10^{2}) + (9 × 10^{1}) + (2 × 10^{0}) + (1 × 10^{-1}) + (4 × 10^{-2}) + (6 × 10^{-3})

**Explanation:**

192.146 = (1 × 10^{2}) + (9 × 10^{1}) + (2 × 10^{0}) + (1 × 10^{-1}) + (4 × 10^{-2}) + (6 × 10^{-3}) is the correct answer.

**6. What is the base number of the binary number system?**

- 2
- 4
- 6
- 8

**Answer:** A) 2

**Explanation:**

The base of the binary number system is 2.

**7. What is the range of numbers used in a binary number system?**

- 0-2
- 0-1
- 1-2
- None

**Answer:** B) 0-1

**Explanation:**

O and 1 numbers are used in the binary number system.

**8. What is the base of the Octal number system?**

- 2
- 4
- 8
- 16
- 10

**Answer:** C) 8

**Explanation:**

The base of the Octal number system is 8.

**9. What range of numbers are used in the octal number system?**

- 0-8
- 1-9
- 0-9
- 0-7

**Answer:** D) 0-7

**Explanation:**

From 0 to 7 numbers are used in the octal number system.

**10. What is the base of the hexadecimal number system?**

- 10
- 16
- 20
- 18

**Answer:** B) 16

**Explanation:**

The base of the hexadecimal number system is = 6.

**11. What is the range of the hexadecimal number system?**

- 0 to 10 and A to F
- 0 to 9 and A to F
- 1-10 and A to E
- 0-9 and A to E

**Answer:** B) 0 to 9 and A to F

**Explanation:**

The range of the hexadecimal number system is: 0 to 9 and A to F.

**12. All unsigned numbers are ____.**

- Positive
- Negative

**Answer:** A) Positive

**Explanation:**

All unsigned numbers are positive.

**13. What is the full form of MSB?**

- Main significant bit
- Minimum significant bit
- Most significant bit

**Answer:** C) Most significant bit

**Explanation:**

MSB stands for the most significant bit.

**14. MSB of signed binary numbers is also known as ____.**

- Most bit
- Min bit
- Signed bit
- Sign bit

**Answer:** D) Sign bit

**Explanation:**

MSB of signed binary numbers is also known as the sign bit.

**15. How many types of representation are there for signed binary numbers?**

- 5
- 4
- 3
- 2

**Answer:** C) 3

**Explanation:**

There are three types of representations for signed binary numbers:

- Sign-Magnitude form
- 1's complement form
- 2's complement form

**16. 1's complement of positive number gives a ____ number.**

- Positive number
- Negative number
- Both

**Answer:** B) Negative number

**Explanation:**

1's complement of a positive number gives a negative number.

**17. 1's complement of negative number gives a ____ number.**

- Positive
- Negative
- Original signed binary number

**Answer:** A) Positive

**Explanation:**

1's complement of a negative number gives a positive number.

**18. If you do two times the one's complement of a binary number including the sign bit, what result you would get?**

- Positive
- Negative
- Original signed binary number

**Answer:** C) Original signed binary number

**Explanation:**

If you do two times the one's complement of a binary number including the sign bit, you will get the original signed binary number.

**19. The 2's complement of positive number gives a ____ number?**

- Negative number
- Positive number

**Answer:** A) Negative number

**Explanation:**

The 2's complement of a positive number gives a negative number.

**20. What will be the 1's complement of 50 in binary number?**

- 110010
- 001101
- 110110

**Answer:** C) 110110

**Explanation:**

First step is to convert the decimal 50 into binary which is equal to 110010, now to find the 1's complement just replace 0 with 1 therefore the final answer is = 001101.

**21. What will be the 1's complement of 30 in binary number?**

- 11110
- 00000
- 11111
- 00001

**Answer:** D) 00001

**Explanation:**

First step is to convert decimal 30 to binary i.e., 11110, now just change the value of 0 to 1 and 1 to 0 therefore the final answer is = 00001.

**22. Binary codes are classified into how many types?**

- 5
- 4
- 3
- 2

**Answer:** D) 2

**Explanation:**

Binary codes are classified into 2 types:

- Weighted codes
- Unweighted codes

**23. Weighted codes are classified into how many types?**

- 5
- 4
- 3
- 2

**Answer:** D) 2

**Explanation:**

Weighted codes are classified into 2 types: positively weighted codes and negatively weighted codes.

**24. What is the full form of BCD?**

- Base decimal code
- Binary dialogue code
- Binary coded decimal
- Base-coded decimal

**Answer:** C) Binary coded decimal

**Explanation:**

BCD stands for binary coded decimal.

**25. How many types of parity codes are there?**

- 5
- 4
- 2
- 1

**Answer:** C) 2

**Explanation:**

There are two types of parity codes: Even parity code and odd parity code.

**26. The value of an even parity bit should be ____ if an even number of ones is present in the binary code.**

- 0
- 1

**Answer:** A) 0

**Explanation:**

If the binary code has an even number of ones, the value of the even parity bit should be zero.

**27. Even parity bit is used only for ____.**

- Error detection
- Error correction

**Answer:** A) Error detection

**Explanation:**

Even parity bit is used only for Error detection.

**28. The value of the odd parity bit should be ____ if an odd number of ones is present in the binary code.**

- 0
- 1

**Answer:** A) 0

**Explanation:**

If there are an odd number of ones in the binary code, the value of the odd parity bit should be zero.

**29. Hamming code is used for ____.**

- Error detection
- Error correction
- None
- Both

**Answer:** D) Both

**Explanation:**

Hamming code is used for Error detection and Error correction.

**30. Which of the following theorem is used to find the complement of the Boolean function?**

- Duality theorem
- DeMorgan's theorem

**Answer:** B) DeMorgan's theorem

**Explanation:**

DeMorgan's theorem is used to find the complement of a Boolean function.

**31. What do you mean by Canonical SoP?**

- Canonical sum of products
- Canonical solution of problems
- Canonical solution of products

**Answer:** A) Canonical sum of products

**Explanation:**

Canonical SoP stands for Canonical sum of products.

**32. Canonical SoP form is also known as ____.**

- Sum of Max terms
- Sum of Min terms

**Answer:** B) Sum of Min terms

**Explanation:**

Canonical SoP form is also known as the Sum of min terms form.

**33. Canonical PoS form is also known as ____.**

- Product of Max terms
- Sum of Max terms
- Product of Min terms
- Sum of Min terms

**Answer:** A) Product of Max terms

**Explanation:**

Canonical PoS is also known as Product of Max terms.

**34. What is the number of cells in 3 variable K-map?**

- 5
- 2
- 6
- 8

**Answer:** D) 8

**Explanation:**

There are 8 cells in 3 variable K-map.

**35. What is the number of cells in 2 variable K-map?**

- 4
- 2
- 6
- 8

**Answer:** A) 4

**Explanation:**

There are 4 cells in 2 variable K-map.

**36. What is the number of cells in 4 variable K-map?**

- 32
- 16
- 20
- 14

**Answer:** B) 16

**Explanation:**

There are 16 cells in 4 variable K-map.

**37. What is the number of cells in 5 variable K-map?**

- 40
- 24
- 32
- 20
- 14

**Answer:** C) 32

**Explanation:**

There are 32 cells in 5 variable K-map.

**38. Ex-OR and Ex-NOR gate comes under which category of the gate?**

- Basic gate
- Special gate
- Universal gate

**Answer:** B) Special gate

**Explanation:**

Ex-OR and Ex-NOR gate comes under the category of special gate.

**39. Which of the following is the universal gate?**

- NAND
- NOR
- Both
- None

**Answer:** C) Both

**Explanation:**

NAND and NOR both come under the category of universal gate.

**40. ____ form is used when the output of a two-level logic realization cannot be achieved using a single logic gate.**

- Non-degenerative
- Degenerative

**Answer:** A) Non-degenerative

**Explanation:**

Non-degenerative form is used when the output of a two-level logic realization cannot be achieved using a single logic gate.

**41. Octal to binary encoder has how many inputs?**

- 2
- 8
- 16
- 1

**Answer:** B) 8

**Explanation:**

Octal to binary encoder has 8 inputs.

**42. A 4*1 mux has how many inputs?**

- 5
- 4
- 2
- 1

**Answer:** B) 4

**Explanation:**

4*1 mux has 4 data inputs, two selection lines, and one output.

**43. What do you mean by PLDs?**

- Programmable Logic devices
- Perfect Logic devices
- Prune Logic devices
- Personal Logic devices

**Answer:** A) Programmable Logic devices

**Explanation:**

PLDs are known as Programmable Logic devices. These are the integrated circuits.

**44. How many types of PLDs are there based on the types of arrays?**

- 5
- 4
- 3
- 2

**Answer:** C) 3

**Explanation:**

On the basis of type of array there are 3 kinds of PLDs:

- Programmable Read Only Memory
- Programmable Array Logic
- Programmable Logic Array

**45. Which of the following statement is correct?**

- PROMs are programmable logic devices with fixed AND and programmable OR arrays
- PROMs are programmable logic devices with fixed NAND and programmable OR arrays
- PROMs are programmable logic devices with fixed NOR and programmable OR arrays

**Answer:** A) PROMs are programmable logic devices with fixed AND and programmable OR arrays.

**Explanation:**

PROMs are programmable logic devices with fixed AND and programmable OR arrays.

**46. Which of the following statement is TRUE about PAL (Programmable array logic)?**

- PAL is a programmable logic device with a fixed NOR array and a programmable OR array
- PAL is a programmable logic device with a fixed AND array and a programmable NOR array
- PAL is a programmable logic device with a fixed OR array and a programmable AND array

**Answer:** C) PAL is a programmable logic device with a fixed OR array and a programmable AND array.

**Explanation:**

PAL is a programmable logic device with a fixed OR array and a programmable AND array.

**47. PAL's outputs will be in the form of a ____.**

- Product of sum
- Sum of products

**Answer:** B) Sum of products

**Explanation:**

PAL's outputs will be in the form of a sum of products.

**48. The threshold gate has how many inputs and outputs?**

- At least one output and only one input
- At least one input and only one output
- Any number of output and inputs

**Answer:** B) At least one input and only one output.

**Explanation:**

The threshold gate has at least one input and only one output.

**49. How do you represent the threshold gate?**

- Via circle
- Via Square
- Via Combinational circuit
- None

**Answer:** A) Via circle

**Explanation:**

A circle represents a threshold gate.

**50. Which of the following statement is correct about the combinational and Sequential circuit?**

- In sequential circuits Only the current inputs determine the outputs, and in combinational circuits, Outputs are determined by both the current inputs and the current state
- In combinational circuits, Only the current inputs determine the outputs and in sequential circuits, Outputs are determined by both the current inputs and the current state

**Answer:** B) In combinational circuits, Only the current inputs determine the outputs and in sequential circuits, Outputs are determined by both the current inputs and the current state.

**Explanation:**

In combinational circuits, Only the current inputs determine the outputs and in sequential circuits, Outputs are determined by both the current inputs and the current state.

**51. Among combinational and sequential circuits in which of the following feedback is not present?**

- Combinational Circuits
- Sequential Circuits

**Answer:** A) Combinational Circuits

**Explanation:**

In combinational circuits, feedback is not present.

**52. How many types of sequential circuits are there?**

- 5
- 4
- 3
- 2

**Answer:** D) 2

**Explanation:**

There are two types of sequential circuits:

- Asynchronous sequential circuits
- Synchronous Sequential circuits

**53. If all of the outputs of a sequential circuit change in response to the active transition of the clock signal, the sequential circuit is said to be ____.**

- Asynchronous
- Synchronous

**Answer:** B) Synchronous

**Explanation:**

If all of the outputs of a sequential circuit change in response to the active transition of the clock signal, the sequential circuit is said to be synchronous.

**54. How many types of triggers are used in sequential circuits?**

- 5
- 4
- 3
- 2

**Answer:** D) 2

**Explanation:**

Two types of triggers are used in sequential circuits:

- Level triggering
- Edge Triggering

**55. How many types of level triggering are there?**

- 2
- 3
- 4
- 5

**Answer:** A) 2

**Explanation:**

There are two types of level triggering:

- Positive level triggering
- Negative level triggering

**56. ____ level triggering occurs when the sequential circuit is operated with the clock signal while it is in Logic High.**

- Positive level triggering
- Negative level triggering

**Answer:** A) Positive level triggering

**Explanation:**

Positive level triggering occurs when the sequential circuit is operated with the clock signal while it is in Logic High.

**57. How many types of edge triggering are there based on the transitions of the clock signal?**

- 5
- 4
- 3
- 2

**Answer:** D) 2

**Explanation:**

There are two types of edge triggering based on the transitions of clock signal:

- Positive level triggering
- Negative level triggering

**58. What is the full form of the SR latch?**

- Set Reset Latch
- Set Remind Latch
- Save Reset Latch

**Answer:** A) Set Reset Latch

**Explanation:**

SR latch stands for Set reset latch.

**59. Which of the following is the drawback of the SR latch?**

- When both S and R are zero, the next state value cannot be predicted
- When both S and R are one, the next state value cannot be predicted
- When both S and R are one, the next state value can be predicted

**Answer:** B) When both S and R are one, the next state value cannot be predicted.

**Explanation:**

SR latch has a drawback i.e., When both S and R are one, the next state value cannot be predicted.

**60. What is the full form of a D latch?**

- Datagram latch
- Dataset latch
- Database latch
- Data latch

**Answer:** D) Data latch

**Explanation:**

Full form of the D latch is the Data latch.

**61. Which of the following is the simplest version of the JK flipflop?**

- T flip-flop
- SR flip-flop
- D flip-flop

**Answer:** A) T flip-flop

**Explanation:**

T flip-flop is the simplest version of JK flip-flop.

**62. The ____ is a collection of flip-flops that are used to store binary data.**

- Log
- Database
- Ledger
- Register

**Answer:** D) Register

**Explanation:**

The register is a collection of flip-flops that are used to store binary data.

**63. The register is known as a ____- register if it is capable of moving bits either to the right or to the left.**

- Flag
- Shift
- Accumulator
- Stack

**Answer:** B) Shift

**Explanation:**

The register is known as a shift register if it is capable of moving bits either to the right or to the left.

**64. An 'N' bit shift register contains ____ flip-flops.**

- N-1
- N+1
- N
- N2

**Answer:** C) N

**Explanation:**

An 'N' bit shift register contains 'N' flip-flops.

**65. ____ shift register is a shift register that accepts serial input and outputs serial output.**

- SISO
- SIPO
- PISO
- PIPO

**Answer:** A) SISO

**Explanation:**

Serial In - Serial Out SISO shift register is a shift register that accepts serial input and outputs serial output.

**66. Shift registers are used as ____.**

- Parallel to serial converter
- Serial to parallel converter
- Sequence generator
- Counters
- All of the above

**Answer:** E) All of the above

**Explanation:**

Shift registers are used as:

- Parallel to serial converter
- Serial to parallel converter
- Sequence generator
- Counters

**67. When a counter counts from 0 to 2N -1, it is referred to as a ____ counter.**

- Binary down counter
- Binary up counter

**Answer:** B) Binary up counter

**Explanation:**

When a counter counts from 0 to 2N- 1, it is referred to as a binary up counter.

**68. How many types of counters are there based on the flip-flops?**

- 5
- 4
- 3
- 2

**Answer:** D) 2

**Explanation:**

There are two types of counters based on the flip flops:

- Asynchronous counter
- Synchronous counter

**69. If the flip-flops do not receive the same clock signal, the counter is referred to as ____.**

- Asynchronous
- Synchronous

**Answer:** A) Asynchronous

**Explanation:**

If the flip-flops do not receive the same clock signal, the counter is referred to as asynchronous.

**70. The synchronous sequential circuits is also known as ____.**

- Finite state machine
- Regular expression
- Grammar

**Answer:** A) Finite state machine

**Explanation:**

Synchronous sequential circuits is also known as Finite state machine.

**71. How many types of Finite state machines are there?**

- 5
- 4
- 3
- 2

**Answer:** D) 2

**Explanation:**

There are two types of FSM:

- Mealy state machine
- Moore state machine

**72. A ____ machine is a finite state machine in which the current state and current input symbol determine the future state.**

- Moore
- Mealy

**Answer:** A) Moore

**Explanation:**

A Moore machine is a finite-state machine in which the current state and current input symbol determine the future state.

**73. What is the Mealy machine?**

- A Mealy machine is a machine in which the output symbol depends upon the present input symbol and the present state of the machine
- A Mealy machine is a machine in which the output symbol depends upon the present input symbol and the next state of the machine
- A Mealy machine is a machine in which the output symbol depends upon the next input symbol and the next state of the machine
- A Mealy machine is a machine in which the output symbol depends upon the next input symbol and the present state of the machine

**Answer:** A) A Mealy machine is a machine in which the output symbol depends upon the present input symbol and the present state of the machine.

**Explanation:**

A Mealy machine is a machine in which the output symbol depends upon the present input symbol and the present state of the machine.

**74. What do you mean by ASM charts?**

- Algorithmic state machine
- Altar state machine
- Algo state machine

**Answer:** A) Algorithmic state machine

**Explanation:**

ASM stands for Algorithmic state machine.

**75. In ASM charts state box is represented in which shape?**

- Oval
- Cube
- Triangle
- Rectangular

**Answer:** D) Rectangular

**Explanation:**

In ASM charts state box is represented in a rectangular shape.

**76. In ASM charts decision box is represented in which shape?**

- Oval
- Cube
- Triangle
- Diamond

**Answer:** D) Diamond

**Explanation:**

In ASM charts decision box is represented in a diamond shape.

**77. In ASM charts conditional output box is represented in which shape?**

- Oval
- Cube
- Triangle
- Square

**Answer:** A) Oval

**Explanation:**

In ASM charts conditional output box is represented in an oval shape.

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