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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2011/
Module Title: Digital Systems 1
Module Code: ELTR
School: Mechanical, Electrical and Process Engineering
Programme Title: Bachelor of Engineering in Electronic Engineering
Programme Code(s): EELXE_7_Y1 EELES_8_Y
External Examiner(s): Dr A Donnellan
Mr I Kennedy
Internal Examiner(s): Mr J O’Sullivan
Instructions: Attempt any three questions. All questions carry equal marks. Ensure that you include the Return Sheet with your answer book.
Duration: Two hours
Sitting: Autumn 2012
Requirements for this examination: N/A
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
You are expected to present your material in a neat and clear fashion. Start each question on a new page. Remember that you have plenty of time for this exam – two hours for three questions.
Q1 (a) For the logic function performed by each of the gates, x , y and z , in Figure 1 below, write down: (i) a statement in plain language describing the function (ii) a truth table (iii) a Boolean expression [6 marks]
(b) Using a truth table, prove that A AB A B [4 marks]
(c) Draw a good sized schematic diagram for the following logic function, (do not minimise) Y A BC C(A B) [6 marks]
(d) On the diagram you drew for (c) above, show the output of each gate if the following input combination is applied: A = 1, B = 0, C = 1 [4 marks]
( x ) ( y ) ( z )
Figure 1
Q2 (a) The binary number system is very awkward for humans to use. If so, why is it so widely used in digital and computer systems? [2 marks]
(b) Convert the decimal number 37 to binary showing all working and explain the reason for the technique used to obtain the result [4 marks]
(c) What system is used to overcome the difficulties experienced by humans when dealing with long binary numbers and draw up a table for this system [4 marks]
(d) Using any long binary value of your choosing, show how the system in (c) allows us to express the value in a more manageable way [2 marks]
(e) In an industrial process, three vats are used for the storage of chemicals. A monitoring system with indicator lamps is needed to show the levels of chemical held. A green lamp will light if any one vat is empty, a blue lamp will light if any two vats are empty and a red lamp will light when all are empty. You are asked to design the logic circuit to control the lamps.
(i) draw a block diagram for this system (ii) complete a truth table for the system (iii) write Boolean expressions for all outputs [8 marks]
CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2011/
Module Title: Digital Systems 1
RETURN SHEET
A
B
C
Y
Figure 3
C
A
B
Y
Name: Return this sheet with your answer book.
