ELEC4601 Microprocessors Lab 2 Tutorial

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ELEC4601 Microprocessors Lab 2 Tutorial
Signal Waveforms and Parallel port programming
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Reading Materials

• From your class notes
• Pin-outs and Pin Functions (pages 66-70)
• Bus Buffering and Latching (page 72)
• Bus Timing (pages 75 - 79)
• From the SDK-86 manual
• OB (Output Byte) Command (page 3-15)
• From the Peripherals Handbook
• 8255A (starting on page 3-100, specifically page
  3-104)
• From the 8086 Hardware Reference Manual
• Look up commands OUT, MOV and JMP (For of clock
  cycles, numbers in brackets are for 186)

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Pre-lab

• For your Pre-Lab
• Calculate the number of clock cycles expected in
  the program fragment of part A (page Lab2-4)
• Find Control Byte value (part B step 1)
• Write the program (part B step 4)
• Further study (from Lab Manual)
• Read Appendix A, logic analyzer operation
• Read Appendix B, in particular the 8255A and DAC
  extensions

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Signal Waveforms

• Part A

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Objectives

• Understand bus cycles / timing
• What do the ALE, WR and RD bits indicate?
• Can you tell what is the happening during each
  clock cycle by looking at ALE, WR, RD and
  contents of the bus?
• Instruction pre-fetching, and the effect of JMP
  on the instruction queue

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Pre-lab

• Calculate the number of cycles the program
  segment should take to execute (page Lab2-4)
• Lab2.asm available on the course web

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Procedure

• Run the program (lab2.asm)
• Infinite loop that continuously moves data from
  register to memory
• Monitor bus signals during program execution
• Logic Analyzer will show the signals (20 bit
  address/data, WR, RD, ALE, PCLK)
• Show the Analyzer waveform to a TA to verify
• Draw the waveforms on the timing diagram in lab
  manual
• (Show your work. Rest of part A can be done after
  the lab)
• Interpret what is happening at each clock cycle
  (Table 1)
• Explain what is happening on the bus during
  program execution (Q. 5-8)

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Logic analyzer view (incorrect!)
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Parallel port programming

• Part B

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Objectives

• Understand how to set up 8255A I/O port
• Understand how to output values to the port
• Understand how to determine control word to
  configure the port
• Understand how the D/A converter works
• Write a program using this information to produce
  a sawtooth waveform
• You should be able to adjust the period and
  amplitude of your waveform by adjusting your code

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DA converter concept

• D/A converter produces converts digital value to
  analogue
• Each data byte you output to D/A converter will
  produce a certain constant voltage level
• Your code will have to make the output a
  continuous (?) sawtooth waveform
• Voltage levels linearly related to data values
  (which range from 00H to FFH)
• Demonstrate your waveform to TA
• Ramp from your pre-lab code
• Modification you made later

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Part B Pre-Lab

• Determine the control word needed for part B
• Write the program for Part B (name it lab2b.asm)
• Try to optimize your coding
• Know how you can adjust the amplitude and period
• Modify program

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Part B Procedure

• Program the I/O port for certain output
• 8255A I/O component is used to interface to CPU
• Control register is used to configure ports
• Use OB (output byte) command from keypad to
  output to ports
• Use OUT command in your program to do the same
• Use this port to send data values to the D/A
  converter
• Find data values that produce specified voltage
  levels
• You will use an oscilloscope to view the D/A
  output
• Your should be able to calculate certain data
  value needed for certain output voltage

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• See you next week!