Digital electronics questions on GATES, Flip Flop, Counters.

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Here we will cover the important question from numerous topic in digital electronics to revise the basic concept on the college level.

These digital electronics questions on GATES, Flip Flop, Counters. Multiplexer/Dmultiplexer , Encoder/Decoder can help you to understand the very basic of digital electronics.

Convert the numbers

1. (3DA)16 = (X)2 find X.

Ans. (3DA)16 in BCD will be (0011 1101 1010)2
X= 0011 1101 1010

2. (0011 0110.0110) = (X)16 find X.

(0011)2 = (3)10


3. Number of bits required to represent 6128 in Binary ?

(1011111110000)2 13 bits.

4. (SqrRoot(41))x = (25)y. find x and y.

4x+y =2y+5
=> 2x-y=2
x=5,y=8 or x=6,y=10 or x=7,y=12 or x=8,y=14

here x and y should be greater then 4 and 5 retrospectively.

5. (11111111)2 = (X)10 find X.

Ans. X = 244

6. (1100.1011)2 = (X)10 find X.

Ans. X = 12.6875

7. (255)12 = (X)2

Ans. (100001001)2

8. (10.625)10 = (X)2

Ans. X = 1010.101

9. Add 1010.1101 adding 101.01 .

Ans. 10000.0001

10. Represent the following in 2s complement.

i) +3 = 1101
ii) +25 = 11001
iii) -5 =1011
iv)-11 = 10101

11. 01000-01001 using 2s compliment.

Ans. (11111)2

12. (6327.4051)8 to decimal.

Ans. (3289.0100)10

14. Realize all the gates using NAND & NOR gates.

NAND gate as other gates
NAND as XNOR gates
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NOR as OR Gate & NOR as AND Gate

NOR as OR & NOR as AND




15. BCD to 7 segment display.

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16. Draw 8:1 multiplexer using 2:1 mux.

8:1 mux using 2:1 mux

ii) Draw 16 : 1 using 4:1 multiplexer.

16:1 multiplexer using 4:1

Application of multiplexer are.

  • Communication system
  • Telephone network 
  • Computer memory 
  • Transmission from the computer system of a satellite
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Application of encoder and decoder.

Encoder applications

  • Aerospace: encoder provides high precision motion feedback while operating in encoder value.
  • Autonomous vehicles and robots : Encoder provide precise, reliable motion feedback in automated robotic application.
  • Converting : encoders provide feedback for speed, direction and distance for precisely controlled operations.
  • Filling : Encoder ensure that the item to be filled is in the correct position before the filling mechanism activates.

Decoder Applications

  • Microprocessor memory systems – selecting different banks of memory.
  • Microprocessor input/output systems – selecting different devices.
  • Microprocessor instruction decoding – enabling different functional units.
  • Memory Chips – enabling different rows of memory depending on address.

BCD to excess-3 code converter.

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Parity Generator

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Characteristic equation for SR,JK,T and D Flip Flop with truth table

SR Flip Flop

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JK Flip Flop

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D Flip Flop

D Flip Flop
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T Flip Flop

T Flip flop

What is Race around condition in JK Flip Flop what are the various techniques to overcome this problem.

For JK Flip Flop, If J+K+1 and clock = 1 for a long period of time, then output Q will be toggle as long as clock remains high which makes the output unstable and uncertain.

race condition in JK flip flop
Condition to overcome racing.
  • t/2 < propagation delay of Flip Flop
  • Edge triggering should be used.
  • Master Slave

Decade Counter

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3 bit asynchronous up-down counter

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3 bit synchronous up-down counter

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