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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2010/
Module Title: Digital Systems 2
Module Code: ELTR
School: Electrical and Electronic Engineering
Programme Title: Bachelor of Engineering in Electronic Engineering Bachelor of Engineering (Honours) in Electronic Systems Engineering
Programme Code: EELES_8_Y1 EELXE_7_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 to include the Return Sheet with your answer book.
Duration: Two hours
Sitting: Summer 2011
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) Draw a full logic diagram and truth table for a clocked S-R flip-flop complete with synchronous and asynchronous inputs. [5 marks]
(b) With reference to the data sheet for the 74LS74 chip, © Motorola , accompanying this paper, give brief answers to the following questions: (i) what type of circuits are found in this chip? (ii) identify the asynchronous inputs to the circuits in the chip (iii) what is the minimum supply voltage for the 74LS74 chip? (iv) briefly explain what is meant by the AC setup symbol th [2 marks]
(c) Complete the timing diagram on the Return Sheet attached to this paper assuming that it applies to a circuit from the 74LS74 chip. [4 marks]
(d) Identify the logic circuit in Figure 1 below and briefly describe its operation. [3 marks]
(e) Using a functional block diagram with pin numbers included, show how the circuit in Figure 1 could be built from 74LS74 chips. [6 marks]
D3 Q
D2 Q
D1 Q
D0 Q
LOAD
CLR
Figure 1
Q4 (a) What is meant by a decoder circuit? [2 marks]
(b) Draw a block diagram and truth table for a 2-bit binary decoder circuit. [4 marks] (c) Write down Boolean equations for each output of the circuit in (a) and hence or otherwise, draw a full logic diagram for this device. [7 marks] (d) Figure 4 below shows a pinout diagram of the 74LS85 IC chip. Identify this chip and briefly describe the function it performs. [4 marks] (e) Assuming the following binary numbers were applied to the 74LS85 device, write down the values you would expect to find on all outputs, for each of these: (i) A = 1011 B = 1001 (ii) A = 0101 B = 0101 (iii) A = 0011 B = 1100 [3 marks]
16 15 14 13 12 11 10 9
1 2 3 4 5 6 7 8
A>B in A>B out A=B out A<B out
B3 B A<B in A=B in
A3 B2 A2 A1 B1 A
Vcc
Gnd
Figure 4
CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2010/
Module Title: Digital Systems 2
Return Sheet
PRE
CLR
D
Q
Q
C
Name: Return this sheet with your answer book
