# DNF 202 DIGITAL ELECTRONICS.

UNIVERSITY EXAMINATIONS: 2015/2016
EXAMINATION FOR THE DIPLOMA IN NETWORK SECURITY AND
COMPUTER FORENSICS
DNF 202 DIGITAL ELECTRONICS
DATE: AUGUST 2016 TIME: 1½HOURS

QUESTION ONE
a) Name the gates in the diagrams below. For each give the truth table. [10 Marks]

b) Give the circuit of a half-adder. Show the truth table and standard logic expression that are
needed for the circuit design [6 Marks]
c) Give a practical logic circuit that can be used for generating random numbers needed in data
encryption. Explain how this is done [4 Marks]
d) List the three steps needed in analogue to digital conversion [3 Marks]
QUESTION TWO
a) Define the terms digital and analogue. Clearly show the difference. Neat waveform diagrams may
be used [6 Marks]
b) Perform the following number conversions [8 Marks]
i. 34.6710 = _______________2
ii. 2B.3E16 = ______________2
iii. 10010.10112 = __________8
iv. 26.78 = ________________2
c) List three applications of computer systems [3 Marks]
d) Give three advantages of digital transmission over the cheaper analogue transmission
[3 Marks]
QUESTION THREE
a) Define the following as used with digital logic [4 Marks]
i. Sequential logic
ii. Counter
iii. Register
iv. Multiplexer
b) Using D-flipflops construct a 4-bit register [4 Marks]
c) Name two main types of counters [2 Marks]
d) Give the circuit and operation of a comparator circuit [6 Marks]
e) Give any two number codes and their use [4 Marks]
QUESTION FOUR
a) Define the term combination logic [2 Marks]
b) Minimise the following logic expressions using the K-map [9 Marks]
3
i. F(ABC) = Ʃm(0,1,2,5,7)
ii. F(ABCD) = Ʃm(0,1,3,4,6,7,8,10,12,13,15)
iii. F(ABC) = Ʃm(1,3,5,6,7)
c) Apart from data storage give three other application of register circuits. Illustrate each with a
block diagram [6 Marks]
QUESTION FIVE
a) Give the truth table for the flip-flops below. Give an application for each [9 Marks]
i. SR Flipflop
ii. D Flipflop
iii. JK Flipflop
b) Explain the invalid state of the SR flip-flop [2 Marks]
c) Give three advantages of digital systems over analogue systems [3 Marks]
d) Give the standard logic expression of the circuit shown below [6 Marks]

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