Tribhuvan University

Institute of Science and Technology


Bachelor Level / first-semester / Science

Computer Science and Information Technology( CSC116 )

Digital Logic

Full Marks: 60 + 20 + 20

Pass Marks: 24 + 8 + 8

Time: 3 Hours

Candidates are required to give their answers in their own words as far as practicable.

The figures in the margin indicate full marks.

Section A

Attempt any two questions.


What is combinational circuit? Design a combinational circuit with four inputs that represent a decimal digit in BCD and four output lines that generate the 1’s complement of the input binary patterns.


What is asynchronous counter? Design asynchronous counter that counts the sequence of 0-1-4-6-7 using T flip-flop.


Implement the Boolean function F(P,Q,R,S) = ∑ (3,4,6,8,9,14) using:

a. 8 to 1 multiplexer

b. PLA

c. Decoder

Section B

Attempt any eight questions.


Perform the following operations:

a. (011101)2 – (110011)2 using 2’s  complement

b. (89344)10– – (98654)10 using 9’s complement.


If f(P,Q,R,S) = ∑(3,4,7,8,14) and d(P,Q,R,S) = ∑(1,6,9,13). Simplify using K-map and design the circuit using minimum number of NAND gates.


What is the drawback of RS Flipflop? Explain D Flip Flop in detail with a logic diagram, characteristics table, and characteristics equation.


Design a full subtractor with necessary tables and logic diagram.


What is shift register? Explain 4 bit SISO and PIPO with timing diagram.


Design an asynchronous mod 11 up counter using T flip flop.


How race condition in JK flipflop can be resolved? Explain.


What is decoder circuit? Design 3 to 8 decoder circuit.


Write short notes on:

  1. State Diagram
  2. Encoder
  3. Parallel Adder