UNIVERSITY EXAMINATIONS: 2014/2015
EXAMINATION FOR THE DIPLOMA IN COMPUTER
MAINTENANCE
DCM 111: DIGITAL ELECTRONICS-III
DATE: NOVEMBER, 2014 TIME: 1½HOURS
INSTRUCTIONS: Answer any THREE Questions.
QUESTION ONE
(a) Give four flip-flops and their truth tables [8 Marks]
(b) Design a four bit ring counter using the simple flipflop [8 Marks]
(c) Give the disadvantages of ring counters [4 Marks]
QUESTION TWO
(a) Define the term synchronous counter [2 Marks]
(b) Give two advantages of synchronous counters [2 Marks]
(c) Design a synchronous mod-9 counter. Show all your working. Idicate your choice of
flipflop [16
Marks]
QUESTION THREE
(a) Give on advantage and one disadvantage of Asynchronous counters [2 Marks]
(b) Design an asynchronous mod-11 counter. Show all your working. Give the reason for
the flipflop choice you have made [10 Marks]
QUESTION FOUR
(a) Define the term clock as used in digital electronics [2 Marks]
(b) Describe the circuit and operation of the 555 timer [8 Marks]
(c) Give the difference between combinational logic and sequential logic [2 Marks]
(d) Using a NAND gate circuit show the operation of a JK flipflop [8 Marks]
QUESTION FIVE
(a) Outline the basic components and operation of a microprocessor [8 Marks]
(b) Outline the use of programmable logic devices, giving examples [6 Marks]
(c) Name three instruments used in making measurements in digital electronics and what
they measure [6 Marks]
