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Cork Institute of Technology
Bachelor of Engineering (Honours) in Electronic Engineering -
Stage 3
(EELXE_8_Y3)
Spring 2008
COMPUTER SYSTEMS
(Time: 3 Hours)
Answer any four questions [each 25 marks] Maximum available marks is 100. Use appropriate comments and indentation in program code. PIC and 68000 instruction sets attached.
Examiners: Mr. P Cogan Prof. G. Hurley Dr. S. Foley
Q1. (a) Describe the operation of the PIC 16F74 microcontroller’s Timer0 module
with the help of a diagram (include only the main components). [6 marks]
(b) Describe the generation of PWM (Pulse Width Modulation) using the PIC 16F74 with particular reference to resolution, PWM frequency and software versus hardware waveform generation. [6 marks]
(c) Write an assembly language program for a PIC 16F74 with a crystal frequency of 4MHz that generates a 5kHz PWM waveform with a 50% duty cycle. [13 marks]
continued overleaf ….
Q2. (a) Discuss the limitations of the PIC 16F74’s analogue to digital converter and suggest methods for improving its accuracy. [6 marks]
(b) Demonstrate how the PIC 16F74 ADC can be used to sample an analogue voltage using an interrupt driven assembly language example. [8 marks]
(c) Design a PIC based controller that implements a satellite dish positioning system. The system must move the satellite dish East or West by driving a d.c. motor in either direction. As the motor rotates a switch briefly closes during each revolution, this can be used to determine the position of the satellite dish. Your controller should receive the position to move to using an EIA-232 (RS-232) serial connection. As the dish approaches the correct position its speed should be reduced to avoid overshooting its target. Draw the circuit diagram for your controller on the attached sheet (showing the pinout for the PIC) and give the algorithm for how your software will operate. State any assumptions that you made about the requirements of the design. [11 marks]
Q3. (a) What is the Semantic Gap problem? Discuss the two microprocessor design approaches, RISC and CISC and how they approach the Semantic Gap problem. Give examples of modern processors based on each technology. What are the respective advantages of each technology? [8 marks]
(b) You have been asked to select the central processing unit for a new line of products. The products are handheld personal digital assistants (PDAs). Discuss which features would be most important in selecting the PDA’s CPU. State which CPU you would select for the product and explain your choice. (^) [8 marks]
(c) Write a note on the work carried out by a cache memory controller in a typical computer system. In particular mention any problems that the cache memory controller may have to overcome and explain what is meant by ‘associativity’ and ‘replacement strategy’. [9 marks]
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Q6. (a) Describe how data is exchanged between application programs over a
network with the help of a diagram illustrating the seven layers of the OSI network protocol model. [8 marks]
(b) Write a note on computer networks that briefly explains; (i) What is meant by TCP/IP? (ii) What is the difference between IP addresses and MAC addresses? (iii) What is meant by network topology and give examples of the main topologies. (^) [9 marks]
(c) With reference to computer networks explain what CSMA is. Briefly describe the three main variations of CSMA. [8 marks]
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PIC Special Function Registers – Bank 0
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Configuration Registers for PIC USART Module (From Data Sheet)
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Configuration Registers for PIC A/D Converter Module (From Data Sheet)
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Configuration Registers for PIC PWM (From Data Sheet)
PWM period = (PR2 + 1) * 4 * T OSC * (TMR2 prescale value)
PWM duty cycle = (CCPR1L:CCP1CON<5:4>) * TOSC * (TMR2 prescale value)
