EE 476: Laboratory 1

Stop watch.

Introduction.

In this assignment you will build a stopwatch. The stopwatch will have a start/stop function and a split function. The split function will copy the current measured interval to the LCD display while leaving the main interval timer (and display) running.

Procedure:

1. Make sure the evaluation board is connected to power and to the PC as specified in the evaluation board description. Turn on the power supply with the switch on the board. An LED in the middle of the board should cycle from red to yellow to green. For this first lab, there should be jumpers on the PortB to the LED header and on PortD to the switch header. Ask your instructor for help if these are not installed.

2. After you define a new project, you can add a C source file and edit it.
   1. Save this code (from the Program Organization page) into your directory. This program blinks LEDs and responds to buttons. It is organized as three task subroutines. You will modify this code in the assignment below.
   2. In the Codevision file menu choose to make a new file. When the prompt comes up, choose Project. When asked if you wish to use CodeWizard, decline the offer. At this point, you have made a new project, now you need to configure it. The configure dialog should be open but if it is not, under the Project menu, choose Configure...
   3. In this dialog box, in the Files tab, add the source code to the project you just defined.
   4. In the Compiler tab, set the Chip type to Mega32.
      Set clock speed to 16 MHz.
      Set (s)printf features to int,width.
   5. In the After make tab, set the Program the Chip checkbox.
      Set CKSEL0 and CKSEL2.These select the clock source.
      You may need to uncheck the Check Signature box.
      Then close the configure dialog.
   6. Click on the compile icon. A message window will open to tell you if there are errors in the code. If there are errors, The open the listing file to see where they are. If the compile is successful, you should be able to download the program to the STK500 board and see some blinking LEDs.
3. You will need to generate a time base for measuring times. I suggest that you use the multiple task timing scheme from this code.
4. Remember that a switch which is pushed reads back a logic zero. One button will need to be debounced. The spilt and reset buttons don't need to be debounced, but the start/stop button will need it, otherwise button bounces will make the stopwatch unreliable.
5. The Liquid Crystal Display (LCD):

   A 16 character, two line (16x2), LCD display will be used as a numerical display. The display we are using has an industry-standard interface. A more detailed data sheet for a similar display shows the command set. There are several aspects of the display you should note:

   • Connections to PORTC as follows:

       [LCD pin]   [Mega32 pin]
        1 GND      GND
        2 +5V      VCC
        3 contrast - 10k trimpot wiper (pin 1 goes to +5; pin 3 to gnd) See below.
        4 RS       PC0
        5 RD       PC1
        6 EN       PC2
       11 D4       PC4
       12 D5       PC5
       13 D6       PC6
       14 D7       PC7 
     

     Trimpot schematic: Bottom view: Image:
     Adjust the LCD contrast using a small screwdriver to turn the trimpot. You may not need the trimpot to adjust the display contrast. You can try just hooking the contrast control (LCD pin 3) to ground.

   • There are cables to connect the 10-pin STK500 header plugs to DIP plugs to make it easy to connect to the usual white protoboards. The connection pinnout is given below.
     
   • Connecting the power backwards may destroy it.
     Always check the polarity before connecting the display.
   • Pin 1 is always marked (in a tiny font) on the LCD display. Some displays have the pins on the top of the display, some on the bottom.
   • The LCD interface to the mcu is documented in the CodevisionC libraries and in a short C program which you can use to test your LCD connections. Note that this program uses a software delay to time the display, something you can never do if your program has to respond to external events.
   • The character representation is identical to ASCII codes for numbers, letters and most symbols. Refer to the data sheet above for a complete listing.
   • The LCD display is arranged as 2 lines of 16 characters and is addressable on a per-character basis.

• All timing must be done with interrupt-driven hardware timers and not with software wait-loops.
• All programs must be in C.
• Produce an C language program which implements a stopwatch with three buttons:
  1. The LCD should be used to display min:sec:tenths for total elapsed time on the first line.
  2. The LCD should be used to display min:sec:tenths for a split time on the second line.
  3. Button one should reset both displays when pushed only if the timer is stopped.
  4. Button two should record the current elapsed time on the split time display when pushed.
  5. Button three should start the timer if it is stopped, and stop it if it is running. This button will need to be debounced.
  6. Stopwatch accuracy should be as good as the MCU crystal oscillator.

Be prepared to demo the program you wrote to your TA in lab.

Your written lab report should include:

• How would you measure time-base accuracy?
• Why did we make you use interrupts rather than wait-loops?
• The scheme you used to detect the pushbutton state. (e.g. polling loop, interrupt)
• Other design aspects of the assignment.
• A heavily commented listing of your code.