# DCM 101 DIGITAL ELECTRONICS. UNIVERSITY EXAMINATIONS: 2014/2015
EXAMINATION FOR THE DIPLOMA IN COMPUTER
MAINTENANCE
DCM 101: DIGITAL ELECTRONICS
DATE: NOVEMBER, 2014 TIME: 1½HOURS

QUESTION ONE
(a) Fill the following table by doing the number conversions [12 Marks] (b) Using diagrams show the difference between analogue and digital systems [4 Marks]
(c) Give two advantages of digital systems [4 Marks]
QUESTION TWO
(a) Using proper diagrams show how analogue signals can be changed into digital signals
[8 Marks]
(b) Name the three basic logic gates. Give hteir symbols and truth tables [9 Marks]
(c) Give meaning to the terms gate, truth table and bit [3 Marks]
QUESTION THREE
(a) A circuit has three inputs (A,B,C) and one output (F). F is high if any two inputs are
low. Develope the truth table for this, the resulting expression and logic circuit
[9 Marks]
(b) Give the truth table and symbols of the NAND and NOOR gates [4 Marks]
(c) Show how AND and NOT gates ca be constructed from NAND gates only [5 Marks]
QUESTION FOUR
Design a half adder circuit using NAND gates only. Show all your working [20 Marks]
QUESTION FIVE
(a) Design a Binary to BCD converter. Show all your working [14 Marks]
(b) Give the reasons for using number codes such as BCD and gray code [2 Marks]
(c) Giving examples show the difference between digital and analogue quantities
[4 Marks]

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