Tribhuvan University

Institute of Science and Technology

2077

Bachelor Level / first-semester / Science

Computer Science and Information Technology( CSC111 )

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.

**Group A**

**Attempt any two questions (2 x 10 = 20)**

1

Design a combinational circuit that generates 9’s complement of a BCD number.

2

Implement the following functions using PLA

- w (A, B, C, D) = Σ(2, 12, 13)
- x (A, B, C, D) = Σ(7, 8, 9, 10, 11, 12, 13, 14, 15)
- y (A, B, C, D) = Σ(0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 15)
- z (A, B, C, D) = Σ(1, 2, 8, 12, 13)

3

Design sequential circuit specified by the following state diagram using T flip-flops.

**Group B**

**Attempt any eight questions (8 x 5 = 40)**

4

List two major characteristics of digital computer. Represent -6 (negative six) 8 bits in signed magnitude, signed 1’s complement and signed 2’s complement respectively. Represent decimal number 4673 in a) octal and b) BCD

5

Where is CMOS suitable to use? Define Power dissipation. Show that the positive logic NAND gate is a negative logic NOR gate and vice versa.

6

Simplify the following function and implement them with two level NOR gate circuit, F(w, x, y, z) = wx’ + y’z’ + w’yz’.

7

Design a full subtractor circuit with three inputs x, y, \(B_{in}\) and two outputs Diff and \(B_{out}\)· The circuit subtracts \(x-y-B_{in}\)., where \(B_{in}\) is the input borrow, \(B_{out}\) is the output borrow, and Diff is the difference.

8

Design 4-bit even parity generator.

9

What is the difference between a serial and parallel transfer? Explain how to convert serial data to parallel and parallel data to serial. What type of register is needed?

10

Explain negative-edge triggered D flip flop with necessary logic diagram and truth table.

11

Illustrate the use of Binary ripple counter and BCD ripple counter.

12

Write Short notes on (Any two)

- RTL
- State Reduction
- POS

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