Digital Electronics MCQ Quiz - Objective Question with Answer for Digital Electronics - Download Free PDF

Last updated on May 30, 2025

Latest Digital Electronics MCQ Objective Questions

Digital Electronics Question 1:

In an asynchronous counter, the clock input of each flip-flop except first flip-flop is connected to:

  1. the same clock source
  2. the output of the previous flip-flop
  3. a separate clock source
  4. a common reset line

Answer (Detailed Solution Below)

Option 2 : the output of the previous flip-flop

Digital Electronics Question 1 Detailed Solution

The correct answer is: 2) the output of the previous flip-flop

Explanation:
In an asynchronous counter (also called a ripple counter):

Only the first flip-flop receives the external clock signal.

Each subsequent flip-flop is triggered by the output (Q or Q̅) of the previous flip-flop, not by a common clock.

This causes a ripple effect, where changes propagate sequentially, leading to a slight delay between stages.

Additional Information
Asynchronous Counter

Asynchronous counters are those counters where the clock of the next stage is obtained from the output of the previous state.

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Digital Electronics Question 2:

_______ interrupt is a positive edge sensitive interrupt and can be triggered with a short pulse.

  1. RST 6.5
  2. RST 7.5
  3. RST 5.5
  4. RST 4.5

Answer (Detailed Solution Below)

Option 2 : RST 7.5

Digital Electronics Question 2 Detailed Solution

The correct answer is: 2) RST 7.5

Explanation:

In the 8085 microprocessor, the RST 7.5 interrupt has unique characteristics:

  • Edge-Triggered:
  • RST 7.5 is positive-edge sensitive, meaning it triggers when the signal transitions from LOW to HIGH.
  • It can be activated by a short pulse (minimum 500 ns wide).
     

Other RST Interrupts:

RST 6.5 and RST 5.5: Level-sensitive (require the signal to remain HIGH until acknowledged).

RST 4.5: Not a standard interrupt in 8085.6

 

Digital Electronics Question 3:

What is the output of a EX-OR gate when both inputs are '1'?

  1. Undefined
  2. Z
  3. 1
  4. 0

Answer (Detailed Solution Below)

Option 4 : 0

Digital Electronics Question 3 Detailed Solution

The correct option is 4

Concept:

Input A Input B Output (A ⊕ B)
0 0 0
0 1 1
1 0 1
1 1 0

From the truth table, it is clear that the output of an EX-OR gate is '0' when both inputs are '1'. This is because the EX-OR gate outputs '1' only when the inputs are different. When both inputs are the same (either both 0 or both 1), the output is '0'. Therefore, the correct answer is option 4.

Digital Electronics Question 4:

A positive edge-triggered T Flip-Flop has T = 1. If the current output Q is 0, what will be the output Q after 3 clock pulses?

  1. 0
  2. Unchanged
  3. 1
  4. Toggles

Answer (Detailed Solution Below)

Option 3 : 1

Digital Electronics Question 4 Detailed Solution

The correct answer is option 3) 1

Concept:

Let's analyze the given problem statement and options in detail:

Given:

  • T = 1
  • Current output Q = 0

Let's analyze the state of Q after each clock pulse:

  1. Initial state Q = 0
  2. After 1st clock pulse: Q will toggle from 0 to 1
  3. After 2nd clock pulse: Q will toggle from 1 to 0
  4. After 3rd clock pulse: Q will toggle from 0 to 1

Therefore, the output Q after 3 clock pulses will be 1.

Digital Electronics Question 5:

What is the Boolean expression for the Carry-out (C) output of a Half Adder?

  1. C = A ⊕ B
  2. C = A OR B
  3. C = A AND B ⊕ Cin
  4. C = A AND B

Answer (Detailed Solution Below)

Option 4 : C = A AND B

Digital Electronics Question 5 Detailed Solution

A half adder circuit is made up of an AND gate with an XOR gate as shown below:

Electronic Mechanic 59 26Q FT Qbank Part 1 Hindi images Q9

  • A half adder is also known as XOR gate because XOR is applied to both inputs to produce the sum
  • Half adder can add only two bits (A and B) and has nothing to do with the carry
  • If the input to a half adder has a carry, then it will neglect it and adds only the A and B bits
  • That means the binary addition process is not complete and that's why it is called a half adder


Sum (S) = A⊕B, Carry = A.B

INPUTS

OUTPUTS

A

B

Sum

CARRY

0

0

0

0

0

1

1

0

1

0

1

0

1

1

0

1

 

 

Top Digital Electronics MCQ Objective Questions

The difference between the two binary numbers 10010000 and 1111001 is:

  1. 11101
  2. 11011
  3. 10111
  4. 10011

Answer (Detailed Solution Below)

Option 3 : 10111

Digital Electronics Question 6 Detailed Solution

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Rules for Binary subtraction are:

1-1= 0

0-1= 1 (with borrow 1)
1-0= 1
0-0= 0

 

1 0 0 1 0 0 0 0
-  1 1 1 1 0 0 1
0 0 0 1 0 1 1 1

Step 1: 0 – 1 = Borrow to make 10 – 1 = 1.
Step 2: 1 – 0 = 1.
Step 3: 1 – 0 = 1.
Step 4: 1 – 1 = 0.
Step 5: 0 – 1 = Borrow to make 10 – 1 = 1.
Step 6: 1 – 0 = 1.
Step 7: 1 – 0 = 1.

Remember: When zero takes 1 as carry from its left side number, '0' will become '10' which is equal to '2' (2-1=1) and if that '10' further gives carry then it will become '1' not '0'.

The output of the logic gate in figure is

F1 Shubham Madhu 07.10.20 D1

  1. 0
  2. 1
  3.  A̅  
  4. A

Answer (Detailed Solution Below)

Option 3 :  A̅  

Digital Electronics Question 7 Detailed Solution

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Concept:

XNOR Gate:

Symbol:

F1 S.B Madhu 02.06.20 D 7

Truth Table:

Input A

Input B

Output

\(Y={\overline{A\oplus B}}\)

0

0

1

0

1

0

1

0

0

1

1

1

 

Output Equation: \(Y={\overline{A\oplus B}}\)

1) If B is always Low, the output is the inverted value of the other input A, i.e. A̅.

2) The output is low when both the inputs are different.

3) The output is high when both the inputs are the same.

4) XNOR gate produces an output only when the two inputs are same.

Analysis:

F1 Shubham Madhu 07.10.20 D1

\(F = \overline{A+0}=\bar A\)

The number of binary digits in the binary representation of 257 are

  1. 8
  2. 9
  3. 7
  4. 10

Answer (Detailed Solution Below)

Option 2 : 9

Digital Electronics Question 8 Detailed Solution

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Solution:

F2 Madhuri Engineering 20.09.2022 D1 V2

The binary representation of 257 is 100000001

∴ The total number of the binary digit in 257 is 9

The minterm expansion of f (P, Q, R) = PQ + QR̅ + PR̅ is

  1. m2 + m4 + m6 + m7
  2. m0 + m1 + m6 + m7
  3. m2 + m3 + m4 + m5
  4. m0 + m1 + m3 + m7

Answer (Detailed Solution Below)

Option 1 : m2 + m4 + m6 + m7

Digital Electronics Question 9 Detailed Solution

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F(P, Q, R) = PQ + QR' + PR'

= PQ (R + R') + (P + P')QR' + P(Q + Q')R'

= PQR + PQR' + PQR' + P'QR' + PQR' + PQ'R'

= PQR + PQR' + P'QR' + PQ'R'

= m7 + m6 + m2 + m4

= m2 + m4 + m6 + m7

Convert the 127 decimal number into binary.

  1. 1100111
  2. 1111111
  3. 1111011
  4. 111111

Answer (Detailed Solution Below)

Option 2 : 1111111

Digital Electronics Question 10 Detailed Solution

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The correct answer is 'option 2'

Concept

Divide 127 by 2. Use the integer quotient obtained in this step as the dividend for the next step. Repeat the process until the quotient becomes 0.

Solution:

Dividend Remainder
127/2 1
63/2 1
31/2 1
15/2 1
7/2 1
3/2 1
1/2 1

Write the remainder from bottom to top i.e. in the reverse chronological order.

This will give the binary equivalent of 127. 

Therefore, the binary equivalent of decimal number 127 is 1111111.

Four statements are given below. Identify the correct statement.

  1. XOR is universal gate
  2. XNOR is a basic gate
  3. XOR is derived gate
  4. XOR is a basic gate

Answer (Detailed Solution Below)

Option 3 : XOR is derived gate

Digital Electronics Question 11 Detailed Solution

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  • AND, OR, NOT gates are the basic gates.
  • The logic gates which are derived from the basic gates like AND, OR, NOT gates are known as derived gates. NAND, NOR, XOR, and XNOR are the derived gates.
  • A universal gate is a gate which can implement any Boolean function without need to use any other gate type. The NAND and NOR gates are universal gates.

What is the decimal equivalent number of binary number 101101?

  1. 45
  2. 90
  3. 40
  4. 8

Answer (Detailed Solution Below)

Option 1 : 45

Digital Electronics Question 12 Detailed Solution

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The correct answer is option 1): 45

Concept:

To convert the binary number 101101 to decimal, follow these two steps:

  • Start from one's place in 101101: multiply one place with 2^0, tens place with 2^1, hundreds place with 2^2 and so on from right to left
  • Add all the products we got from step 1 to get the decimal equivalent of 101101. Using the above steps, here is the work involved in the solution for converting 101101 to a decimal number (Don't forget that we start from one place to so on...)
    • Decimal equivalent of "1" = 1 × 2^0 = 1
    • Decimal equivalent of "0" = 0 × 2^1 = 0
    • Decimal equivalent of "1" = 1 × 2^2 = 4
    • Decimal equivalent of "1" = 1 × 2^3 = 8
    • Decimal equivalent of "0" = 0 × 2^4 = 0
    • Decimal equivalent of "1" = 1 × 2^5 = 32
    • The decimal equivalent of "101101" =   45
    • Here is the final answer, The binary number 1011012 converted to decimal is therefore equal 4510

In Boolean algebra, (A.A̅) + A =?

  1. A
  2. 0
  3. 1

Answer (Detailed Solution Below)

Option 1 : A

Digital Electronics Question 13 Detailed Solution

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(A.A̅) + A

= 0 + A = A

All Boolean algebra laws are shown below:

Name

AND Form

OR Form

Identity law

1.A = A

0 + A = A

Null Law

0.A = 0

1 + A = 1

Idempotent Law

A. A = A

A + A = A

Inverse Law

AA’ = 0

A + A’ = 1

Commutative Law

AB = BA

A + B = B + A

Associative Law

A(B.C) = (A.B)C

(A + B) + C = A + (B + C)

Distributive Law

A + BC = (A + B) (A + C)

A (B + C) = AB + AC

Absorption Law

A (A + B) = A

A + AB = A

De Morgan’s Law

(AB)’ = A’ + B’

(A + B)’ = A’B’

Which of the following is fastest memory?

  1. Secondary Memory
  2. Auxiliary Memory
  3. Cache Memory
  4. Virtual Memory

Answer (Detailed Solution Below)

Option 3 : Cache Memory

Digital Electronics Question 14 Detailed Solution

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The Correct Answer is "Cache Memory".

Important Points

Cache Memory :

  • Cache Memory is a special very high-speed memory.
  • It is used to speed up and synchronizing with a high-speed CPU. Cache memory is costlier than main memory or disk memory but economical than CPU registers.
  • Cache memory is an extremely fast memory type that acts as a buffer between RAM and the CPU.
  • It holds frequently requested data and instructions so that they are immediately available to the CPU when needed.
  • Cache memory is used to reduce the average time to access data from the Main memory.

Additional Information

Secondary Memory​ :

  • It is non-volatile, i.e. it retains data when power is switched off.
  • It is large capacities to the tune of terabytes.
  • It is cheaper as compared to the primary memory.
  • Depending on whether the Secondary memory device is part of the CPU or not, there are two types of secondary memory – fixed and removable.

                                                        F1 Nakshtra Ravi 27.08.21 D1

 Auxiliary Memory :

  • Auxiliary memory is the non-volatile memory lowest-cost, highest-capacity, and slowest-access storage in a computer system.
  • It is where programs and data kept for long-term storage or when not in immediate use.
  • Such memories tend to occur in two types-sequential access (data must access in a linear sequence) and direct access (data may access in any sequence).
  • The most common sequential storage device is the hard disk drives, whereas direct-access devices include rotating drums, disks, CD-ROMs, and DVD-ROMs.
  • It used as permanent storage of data in mainframes and supercomputers.

 

Virtual Memo :

  • A computer can address more memory than the amount physically installed on the system.
  • This extra memory is actually called virtual memory and it is a section of a hard disk that's set up to emulate the computer's RAM.
  • The main visible advantage of this scheme is that programs can be larger than physical memory.
  • Virtual memory serves two purposes.
    • First, it allows us to extend the use of physical memory by using the disk.
    • Second, it allows us to have memory protection because each virtual address is translated to a physical address.

The minimum number of 2-input NAND gates required to implement a 2-input XOR gate is

  1. 4
  2. 5
  3. 6
  4. 7

Answer (Detailed Solution Below)

Option 1 : 4

Digital Electronics Question 15 Detailed Solution

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The number of 2-input NAND gates required to implement a 2-input XOR gate is 4.

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Similarly, the number of 2-input NOR gates required to implement a 2-input XNOR gate is 4.

26 June 1

Logic Gates

Min. number of NOR Gate

Min. number of NAND Gate

NOT

1

1

AND

3

2

OR

2

3

EX-OR

5

4

EXNOR

4

5

NAND

4

1

NOR

1

4

Half-Adder

5

5

Half-Subtractor

5

5

Full-Adder

9

9

Full-Subtractor

9

9

 

 

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