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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2011/
Module Title: Digital Systems 1
Module Code: ELTR
School: Electrical and Electronic Engineering
Programme Title: Bachelor of Engineering in Electronic Engineering
Programme Code(s): EELXE_7_Y 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: Winter 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) For each of the logic gates, NOR, AND, and XNOR, write down the following: (i) a logic symbol (ii) a truth table (iii) a Boolean expression [6 marks]
(b) For the logic circuit, Figure 1 on the Return Sheet , write down the exact Boolean equation for the output Y. [3 marks]
(c) Complete the timing diagram on the Return Sheet , for this circuit. [5 marks]
(d) In your answer book, re-draw the circuit in Figure 1 using NOR gates only. What is the advantage of carrying out the above exercise on this circuit? [6 marks]
Q2 (a) What is meant by a base-16 counting system? Identify a base-16 system and state why it is widely used in digital systems. [2 marks]
(b) Construct a table showing the decimal, binary and hex equivalents for all possible 4-bit binary numbers. [3 marks]
(c) Use the table in (b) to carry out the following conversions: (i) 1010011110 2 to hexadecimal (ii) D49 16 to binary [2 marks]
(d) Perform the following conversions showing all working (i) 17 10 to binary (ii) 110101 2 to decimal [4 marks]
(e) Why is the two’s complement binary number system used in digital electronics? [1 mark]
(f) The value 10110010 2 is an 8-bit two’s complement binary number. Convert this value to decimal. [3 marks]
(g) Using 8-bit two’s complement numbers throughout, perform the following arithmetic operations in binary and indicate if the result is positive or negative in each case. (i) 7310 – 5910 (ii) 5910 – (^7310)
(Note: 73 10 = 1001001 2 5910 = 111011 2 ) [5 marks]
CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2011/
Module Title: Digital Systems 1
RETURN SHEET
A
B
C Y
Figure 1
C
A
B
Y
Name: Return this sheet with your answer book.
