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Cork Institute of Technology
Bachelor of Engineering (Honours) in Electronic Engineering- Stage 3
(NFQ Level 8)
Autumn 2006
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 1kHz square wave. [13 marks]
Q2. (a) The PIC is classed as a microcontroller. Explain what this means and discuss (using examples) the differences between microcontrollers and microprocessors. (^) [6 marks]
(b) Describe analogue to digital conversion using the internal ADC of the PIC 16C74. Demonstrate how the PIC 16C74 ADC can be used to sample an analogue voltage using an assembly language example. [9 marks]
(c) Design a PIC based controller that measures humidity and controls an alarm and a mains operated air conditioning unit. The controller maintains the average humidity at a pre-set value by reading the sensor. It turns on the air conditioning unit when the humidity is above the desired value. The controller sounds the alarm if the humidity rises above an upper threshold or drops below a lower threshold. An alarm mute button will de-activate the alarm for 10 minutes. The humidity sensor produces a square wave in the range of 6kHz to 7kHz, the frequency of which is directly proportional to the humidity.
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. [10 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) When designing a processor there is a trade off between functionality/cost and performance. Discuss this and describe the factors that influence processor performance, how performance is measured, and techniques for improving performance. [8 marks]
(c) Using the following statistics, describe and justify the micro-processor features which are implemented in RISC processors to improve performance over CISC processors. Operand Types Operation Types Frequency in C language programs Integer Constant 20% Assignment 38% If 43% Scalar Variable 55% Loop 3% Goto 3% Array/Structure 25% Call 12% Other 1% 6 or less arguments per procedure call > 98% of time 6 or less scalar variables per procedure > 92% of time Typical depth of function calls 8. [9 marks]
Q5. (a) Discuss the hardwired control of processor execution and in particular how the
state diagram might be realised in hardware. [10 marks]
(b) Figure 1 shows the execution network for a simple microprocessor. By forming the controlled graph and connectivity matrix determine its disconnecting set. Use this disconnecting set to determine the format for an instruction set based on independently coded field micro-instructions. How would this be decoded? [15 marks]
Fig. 1
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) Discuss the concept of medium access control in computer networks and comment on the design issues of multiple access control. In particular refer to where the medium access control may be implemented and the factors influencing performance. [8 marks]
(c) Briefly explain the concept of carrier sensing and describe the operation of the CSMA/CD protocol used for medium access control in Ethernet LANs. [9 marks]
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