Exam Revision

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Exam Revision  
EE1A2 

• S. I. Woolley
• Electronic, Electrical and Computer Engineering

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Contents

• Learning outcomes.
• Revision suggestions.
• Exam suggestions.
• Writing code in the exam.
• Common mistakes
• Revision questions (and notes)

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Summary of Learning Outcomes

• This course was designed to provide
• an understanding of the basic principles of
  microprocessors and appreciate the difference
  between microprocessors, microcontrollers and
  DSPs (digital signal processors),
• a working knowledge of the PIC16F84
  microcontroller,
• experience of assembler programming and a basic
  appreciation of embedded systems.  

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Revision Suggestions

• Read/work through course materials and examples.
• Look at past exam questions so that you are
  familiar with the style of questions.
• See on-line revision materials and the University
  exam paper database http//www.exampapers.bham.ac.
  uk.
• For this subject a keyword search may not work
  because of varied abbreviations for the long
  title. When using this database always be very
  careful that you are reading the right
  examination paper.
• Note in previous years a different number of
  questions were required.
• Time your attempts at questions.
• Work out your exam technique in advance. e.g.,
  allocate a set amount of time to read through all
  questions carefully.

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Exam Suggestions

• Take a calculator.
• Read questions carefully.
• Keep a close eye on the time.
• Keep descriptive answers short and to the point.
  
• Take note of how many marks are assigned to each
  question and dont spend long on questions with
  few marks.
• Use diagrams, tables or bullet-point lists if
  useful.

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Writing Code in the Exam

• We have referenced different code structures
  during the course. These include code segments,
  templates, subroutines and programs.
• Segments are lines of code.
• Templates are code frameworks (define the
  structure of components but dont contain any
  actual instructions)
• Subroutines are the component program tasks
  completed by a return instruction.
• Programs are full program listings including
  header with device and function fields.
• You will not be asked to write a full program
  listing in the exam.
•  

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Writing Code in the Exam

• Use the instruction set and/or register file map
  and information provided.
• READ THE QUESTION VERY CAREFULLY
• (dont write components that are NOT required)
• You could use a simple flow diagram to get you
  started.
• Comment your code (keep comments clear and
  concise)
• Do you need supporting equates or org statements?
  If the question asks for them they will be worth
  marks.
•  

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Common Mistakes

• that lose marks
• Misreading the question.
• Not using the register file list or instruction
  list.
• Fundamental errors (e.g., errors of the type
  advantage of TMR0 delay over software delay is
  that it is faster)
• Most common major loss of marks occurs when no
  attempt at all is made of a component.
• that dont lose marks
• Slightly different time delay times (our
  approximation is only an approximation - slightly
  different counter values are fine)
• Misspelling generally loses no marks unless, for
  example, a valid instruction is misspelt as a
  different instruction
• E.g., no lost marks for misspelling interrupt.

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Course Revision Questions for you to try

• What is the PIC16F84?
• (A descriptive summary of the most important
  points)
• Write a simple template for a PIC assembler
  program that shows the reader the order of the
  basic contents of PIC assembler file. (For the
  program header comments, list only the important
  fields. )
• (Think of the content of a typical program what
  does it contain and in what order?)
• Write a simple program segment (with supporting
  equates and comments) to configure PORTA pins as
  inputs and PORTB pins as outputs.
• What is the purpose of a data table how is it
  implemented in PIC assembler and why is it done
  this way?
• What are the contents of the INTCON register and
  what are their function? (exact bit names and
  locations not required).
• Briefly explain the advantages of TMRO over a
  software delay.
• Most PIC16F84 instructions take 1 clock cycle to
  execute. Identify all the instructions which
  take always and which sometimes take longer.
  Explain why they take longer.
• Write a 1/20 s second nested loop software time
  delay.

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Notes on Selected Questions

• TMR0 is the hardware timer. The software time
  delay ties up the processor. Using TMR0 means
  the processor is free to do other things. (It
  isnt faster! )
• TMR0 overflow is one of the 4 interrupts on our
  processor.
• The instructions all take one clock cycle except
  instructions which involve a program branch.
  Identifying these is often an exam question.
• BTFSS and BTFSC and DECFSZ and INCFSZ all take
  one or two clock cycles.
• BTFSS and BTFSC are useful bit test
  instructions. Test is a bit is set or clear and
  skip (the next line in the program) if the
  condition is satisfied.

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The Basic Nested-Loop Time Delay

• This is the 0.2s nested loop time delay from your
  lecture notes.
• Several exam questions in the past have required
  a time delay that is a simple fraction of 0.2s
  (1/5 s), for example, 0.1s or 1/20 s. These can
  be achieved by simply halving or quartering
  MCOUNT.
• For 0.2s delay MCOUNT255 (0xFF)
• For 0.1s delay MCOUNT128 (0x80)
• For 0.05s delay, MCOUNT64 (0x40)
• etc.

DELAY MOVLW 0XFF MOVWF MCOUNT GET_N MOVLW 0
XFF MOVWF NCOUNT DEC_N DECFSZ NCOUNT,F GOTO
DEC_N DECFSZ MCOUNT,F GOTO GET_N RETURN
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Time Delay with Flowchart

• DELAY MOVLW 0XFF
• MOVWF MCOUNT
• GET_N MOVLW 0XFF
• MOVWF NCOUNT
• DEC_N DECFSZ NCOUNT,F
• GOTO DEC_N
• DECFSZ MCOUNT,F
• GOTO GET_N
• RETURN

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Summary

• Revision suggestions.
• Exam suggestions.
• Writing code in the exam.
• Common mistakes
• Revision questions (and notes)

14
Thank You and Good Luck  
 

• S. I. Woolley
• Electronic, Electrical and Computer Engineering