# BIT 1202  DIGITAL ELECTRONICS KCA Past Paper

UNIVERSITY EXAMINATIONS: 2010/2011
FIRST YEAR STAGE EXAMINATION FOR THE DEGREE OF BACHELOR
OF SCIENCE IN INFORMATION TECHNOLOGY
BIT 1202: DIGITAL ELECTRONICS
DATE: AUGUST 2011 TIME: 2 HOURS
INSTRUCTIONS: Answer question ONE and any other TWO questions

Question One
a) Write down the general expression for a number in base-r system. [1 Mark]
b) Do the following conversions:
i) (41.75)10 to binary [3 Marks]
ii) (513)10 to octal [3 Marks]
iii) (FFA)16 to decimal [3 Marks]
c) Find:
i) The 10’s complement of (754)10 and (378)10, [3 Marks]
ii) The difference (754-378) using 10’s complement [3 Marks]
iii) Evaluate the 2’s complement of (1010100)2 [3 Marks]
iv) Using 2’s complement find (1000011)2- (1010100)2. [3 Marks]
d) Represent (15)10 in :
i) Binary number [3 Marks]
ii) Binary code [3 Marks]
e) What is the binary result of the multiplication of unsigned binary numbers (10111010)2 and (111)2?
[3 Marks]
Question Two
a) Implement the function y = ab + ab −
using logic gates [4 Marks]
b) Write down the dual of the following Boolean expressions:
(i) x + y = y + x [4 Marks]
(ii) x( y + z) = xy + xz [4 Marks]
c) Find the complements of the following function:
i) A′BC′ + A′B′C [4 Marks]
ii) A(B′C + BC) [4 Marks]
Question Three
a) Define a flip-flop and explain how it works using a truth table. [6 Marks]
b) Distinguish between a combinational circuit and a sequential circuit. [4 Marks]
c) Describe the how a clock signal is incorporated in a D-Type Flip-flop. [5 Marks]
d) Using an illustration show how a four bit shift register can be implemented using D-Type Flip-flops
[5 Marks]
Question Four
a) Construct the Karnaugh map represented by the function F(x, y,z) = ∑(1,4,5,6). Write down the
algebraic expression for the POS, SOP and the minimized function. [10 Marks]
b) Draw the Karnaugh map for the Boolean function:
F(A, B,C, D) = ∑(0,1,8,9,10,11,13,15) With don’t care set d(A, B,C, D) = ∑(2,5,6,7,14) .
Write down the algebraic expression for the POS, SOP and the minimized function. [10 Marks]
Question Five
a) What is a multiplexer? [2 Marks]
b) Explain with the aid of a diagram how a two-input multiplexer works. [4 Marks]
c) Study the circuit below and construct a truth table. [10 Marks]

d) Explain the function of the circuit. [4 Marks]

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