### Exam Year

Tribhuvan University

Institute of Science and Technology

2080

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.

1

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.

2

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

3

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.

4

Perform the following operations:

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

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

5

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.

6

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

7

Design a full subtractor with necessary tables and logic diagram.

8

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

9

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

10

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

11

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

12

Write short notes on:

1. State Diagram
2. Encoder