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Digital Electronics Question Paper

Digital Electronics

Course:Electrical And Electronics Engineering.

Institution: University Of Nairobi question papers

Exam Year:2002

B.Sc. (Electrical and Information Eng.) Third Year Semester - 1
DIGITAL ELECTRONICS
Time : 02 Hours Maximum Marks : 75
Instruction to Candidates:
1) Section - A is Compulsory.
2) Attempt any Nine questions from Section - B.

Section - A
(15 × 2 = 30)

Q1)
a) Why should one study octal & Hexadecimal systems when the digital
machine understands only binary system?
b) Simplify the Boolean equation (A + AB).
c) Where do we use signed binary number?
d) Convert decimal 1000 to octal and Hexadecimal system.
e) What is the utility of floating point representation of numbers?
f) Write the truth table of 2-input Ex-NOR gate.
g) How NOT gate function can be obtained from NOR gate?
h) Explain where do we use MUX?
i) What is the function of an Encoder?
j) Define with example, a combinational circuit.
k) Draw a labelled block diagram of a -ve edge triggered J-K Flip Flop.
l) Explain difference between volatile and Non-volatile memories.
m) Explain what do you mean by secondary memories.
n) What are the applications of D-Flip Flop?
o) Where do we use DC PRESET and DC CLEAR terminals in Flip

Section - B
(9 × 5 = 45)

Q2) If A = 1001 and B = 1100 (Both in binary) find A+B and A–B
( by 2’s complement method)
Q3) Convert
(a) Decimal 200.154 to binary octal and hexadecimal systems.
(b) Hexadecimal FF to octal.
Q4) Express the Boolean function F = xy + x'z in a product of maxterm form.
Q5) Given the following Boolean function:
F = A'C + A'B + A.B'C + BC
(a) Express it in sum of minterms.
(b) Find the minimal sum of products expression.
Q6) Simplify the following Boolean function F together with the don’t care
conditions d; then express the simplified function in sum of minterms.
f(x, y, z) = S (0, 1, 2, 4, 5)
d(x, y, z) = S (3, 6, 7)
Q7) Write the truth table of Half-subtractor and from it realize its circuit.
Q8) Write the truth table of a Full Adder and then derive its circuit in terms of
half adders.
Q9) Draw the circuit of 3 to 8 decoder and explain it.
Q10) (a) Draw the symbols of the various logic gates you have studied.
(b) Explain how a demultiplexer ( 1 to 8) function can be obtained from a
3 to 8 decoder.
Q11) Derive the circuit of an edge triggered J-K Flip Flop from the basic S-R
Flip Flop. Discuss its truth table. How race around problem can be solved
in a J-K Flip Flop?
Q12) Discuss:
(a) Classification of memories.
(b) Advantages of semiconductor memories.
(c) Explain the difference between static and dynamic memories.
Q13) Draw the circuit of an S-R Flip Flop using NOR gates . Write its truth
table and explain why there is a forbidden state. Is there any racing, if so
explain it?

Digital Electronics Question Paper

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