Digital Logic 2067

Question Paper Details
Tribhuwan University
Institute of Science and Technology
2067
Bachelor Level / Second Semester / Science
Computer Science and Information Technology ( CSC-151 )
( Digital Logic )
Full Marks: 60
Pass Marks: 24
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.

Long Answer Questions:

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Attempt any TWO questions. (2x10=20)

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1. What is the magnitude comparator? Design a logic circuit for 4 bit magnitude comparator and explain it.

10 marks
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2. What do you mean by full adder and full subtractor? Design a 3 to 8 line decoder using two 2 to 4 line decoder and explain it.

10 marks
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3. What is JK master slave flip-flop? Design its logic circuit, truth table and explain the working principle.

10 marks
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Short Answer Questions:

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Attempt any EIGHT questions. (8x5=40)

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4. Convert the following hexadecimal number to decimal and octal numbers

(a) 0FFF (b) 3FFF

5 marks
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5. Design a half adder logic circuit using NOR gates only.

5 marks
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6. Proof the 1st and 2nd law of De Morgan’s theorems with logic gate and truth table.

5 marks
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De-Morgans Theorem

De Morgan’s theorem is used to convert OR type of expression into AND type and vice-versa.It is further divided into two different types;

1st law:

It state that the total complement of sum is equal to the product of individual complement. i.e. (A+B)’=A’ ٠B’


Proof:

Input

Output

A

B

(A+B)’

A’ ٠B’

0

0

1

1

0

1

0

0

1

0

0

0

1

1

0

0



2nd law:

It state that the total complement of the product is equal to the sum of individual complement. i.e. (A٠B)’ =A’+B’

Proof:

Input

Output

A

B

(A٠B)’

A’+B’

0

0

1

1

0

1

1

1

1

0

1

1

1

1

0

0



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7. What do you mean by Universal gate? Realize the following logic gates using NOR gates.

(a) OR gate (b) AND gate

5 marks
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An 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.

NOR gate as a Universal Gate

To prove that any Boolean function can be implemented using only NOR gates, we will show that the AND, OR, and NOT operations can be performed using only these

Thus, the NOR gate is a universal gate since it can implement the AND, OR and NOT functions.

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8. Draw a logic circuit of 4 x 1 multiplexer.

5 marks
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9. What is flip-flop? Mention the application of flip-flop.

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10. Explain the Ripple Counter.

5 marks
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11. Design the decimal adder.

5 marks
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12. What do you mean by shift registers? Explain.

5 marks
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13. Write short notes on (any two):

a. Decoder b. Integrated circuit c. PLA.

5 marks
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