CE-2800 Embedded Systems Software
Lab 7: Dual-channel Voltmeter

Objectives

• Become familiar with assembly language program design and instructions
• Use assembly language branch instructions to implement conditional logic
• Use assembly language instructions to implement subroutines and subroutine calls
• Use device driver subroutines to initialize and read the keypad
• Use the A/D subsystem to measure external voltages
• Use the interrupt subsystem of the Atmega32
• Develop device drivers to control the LCD display and USART

Assignment

In this lab you will write a program that, using the D/A converter subsystem of the Atmega32, measures and displays the voltages applied to PortA pins PA0 and PA1 from an external power supply (on the lab bench). Your program will be interrupt-driven; that is, these conversions will only take place when external interrupts (caused by pushbuttons INT0 and INT1) occur.

Hardware Configuration

• The LCD panel should be connected to the USART.
• PortB configured for digital output.
• A/D subsystem enabled on PortA pins
• Power supply on lab bench attached to ground (black lead) and PortA pins PA0 and PA1 (red leads). WARNING: Use extreme caution when setting the output voltages from the power supply to PA0 and PA1 to avoid burning out your Atmega32 chip! Do not exceed 5V.

Program Functionality

• Your "main" program should be placed in a file named Lab7.asm, and implement subroutines that

  1. Initialize PortB for digital output
  2. Initialize PortD for digital input, with the pull-up circuitry activated
  3. Initialize INT0 and INT1 external interrupts to trigger falling edge (button press)
  4. Initialize/enables the A/D subsystem,  A/D interrupts, disables auto-trigger (via ADCSRA register)
  5. Initialize the LCD display so that the first line displays "Pin 0: " and the second line displays "Pin 1: ".
• Once these initializations have been done, your program should enter an endless loop that implements the bouncing light of Lab 2.
   
• When the INT0 button is pressed, the generated interrupt should trigger an ISR named INT0_ISR which:

  1. Configures A/D converter to sense voltage on PA0 (via ADMUX register)
  2. Starts the A/D conversion (via ADSCRA register)
  3. Clears a 1-byte "flag" variable in SRAM to indicate that A/D conversion of PA0 is in progress
  4. Returns
• Similarly, when the INT1 button is pressed, the generated interrupt should trigger an ISR named INT1_ISR which:
  1. Configures A/D converter to sense voltage on PA1 (via ADMUX register)
  2. Starts the A/D conversion
  3. Sets the 1-byte "flag" variable in SRAM  to indicate that A/D conversion of PA1 is in progress
  4. Returns
      
• Once either INT0 or INT1 interrupts start the A/D conversion process, the A/D will in turn cause an interrupt when the conversion is complete. The A/D interrupt should trigger the execution of an ISR named AD_ISR. This ISR should:
  1. Check the SRAM "flag" variable to determine which pin (PA0 or PA1) has just been measured
  2. Move the values from the ADCH and ADCL registers into the X register for subsequent display via the displayValue16 subroutine (described below)
  3. Call the appropriate LCD display subroutines to display the voltage that has just been measured. If PA0, then the first line of the display should display the voltage (leaving the second line as is), and if PA1 has just been measured, then the second line of the display should be updated (leaving the first line as is). Since the A/D will be measuring a voltage that can vary anywhere between 0 and 5V, the value in the X register will vary from 0 to 1023. Thus, when 1V is measured, the X value would be around 204 (0x00CC), and the bottom line of the LCD should display "Pin 1: 0x00CC V"
  4. Return

  Since the INT0, INT1, and A/D interrupts occur arbitrarily (and the associated ISR's execute very quickly), the main program that causes the LEDs to bounce back and forth should never appear to pause to any significant extent, although you may observe slight hesitation in the progress of the bouncing LEDs as the ISR's execute.

  The flowchart for the program looks something like this:

  

LCD display driver extensions

You'll also be implementing new functionality into your LCD display library display_dd.asm: You must add a new subroutine, named displayValue16, that (at the current cursor location) outputs the hexadecimal representation the value contained in the 16-bit X register (thus the X register is the "argument" to this new subroutine). As an example, if the X register contains the value 1, then 0x0001 should appear on the display. Similarly, if the X register contains the value 1000, then 0x03E8 should appear.

Demonstration

You must demonstrate your working program on your board before the lab next week.

Lab Submission (due 11:00pm, Tuesday, January 31, 2012)

For your submission, you need only supply your working, fully commented Lab7.asm and display_dd.asm.

Upload your submission through Blackboard (assignment "Lab 7").

Be sure to keep copies of all your files, in case something gets lost.

Grading

Your lab grade will be determined by the following factors:

Program - comments and formatting are important aspects of assembly language programming! And it has to work correctly.

Timeliness of submission as stated in the course policies.