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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2009/
Module Title: Microprocessor Systems 2
Module Code: ELTR
School: Electrical and Electronic Engineering
Programme Title: Bachelor of Engineering in Electronic Engineering
Programme Code: CR_EELXE_7_Y
External Examiner(s): Dr A Donnellan Dr P O’Sullivan
Internal Examiner(s): Mr J O’Sullivan
Instructions: Attempt any three questions. All questions carry equal marks. Ensure you return the before-and-after sheet with your answer book.
Duration: Two hours
Sitting: Summer 2010
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 answers in a neat and tidy fashion Start each question on a new page Remember that there is plenty of time – two hours to do three questions
Q1 (a) Briefly explain what is meant by a subroutine and list three advantages of using subroutines in a computer program. [4 marks]
(b) In a general purpose computer a memory-based stack is used to facilitate subroutines. Explain what is meant by a stack and the role it plays in the operation of subroutines [4 marks]
(c) Every subroutine should be terminated by a return instruction, which in the case of the MC68000 MPU is the RTS instruction, ($4E75 in machine code). Describe what happens during the fetch and execute cycles when the MPU encounters the opcode $4E75 in a program. [4 marks]
(d) Below is a simple subroutine that we studied during the course to multiply two small 16-bit values, X and Y, using successive addition. There are two logical errors in this subroutine; identify them and write the corrected code with comments added to each line.
MULT ADD.W D1,D SUB.W #1,D BNE MULT [5 marks]
(e) Write a segment of main program in conjunction with the above subroutine to get X and Y from memory, multiply them together and print out the result on the VDU using system subroutine PRWRD. [3 marks]
Q2 Figure 1 attached to this paper shows how a block of read/write memory could be installed in a simple 8-bit microcomputer, using four RAM chips. Study the diagram and the accompanying extract from the data sheet for the 74LS139 chip, © Motorola , and answer the following questions, showing all working where appropriate.
(a) Determine the overall amount of RAM in the block. [4 marks]
(b) What function is performed by A0 – A9 on the RAM chips? [2 marks]
(c) Explain what is meant by logic conflict and how it is avoided in this circuit. [2 marks]
(d) What function is performed by the 74LS139 chip and what is the advantage of using such a chip in this circuit? [2 marks]
(e) With the aid of the data sheet for the 74LS139 chip, draw a full addressing map for this block of RAM. [4 marks]
(f) What function is performed by control line AS and what happens in the circuit when this line goes HIGH? [2 marks]
(g) Describe what happens in the circuit in Figure 1 when the MPU executes the instruction MOVE.B $ABFF,D0 [4 marks]
CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2009/
Module Title: Microprocessor Systems 2
BEFORE-AND-AFTER TABLE
Question 3(d)
Name: Return this sheet with your answer book
X N Z V C
0 1 0 1 0
Registers before Flags before Instruction Registers after Flags after
D0: 98765432
D1: 23456789
D0: 19A42B6A
D1: B72D
D0: 7125BA9C
1 1 0 1 0
X N Z V C
X N Z V C
1 0 0 1 0
MOVE.W D1,D
CMP.B D0,D
AND.B #$0F,D
D0:
D1:
X N Z V C
D0:
D1:
X N Z V C
D0:
X N Z V C
D0: 41D
X N Z V C
0 1 0 1 0
ROL.B #2,D0 D0:
X N Z V C
