This week, the assignment was to add a button (between an empty pin on the microcontroller and ground) to a small board design given to us and alter the code for it (both in assembly and in C) to make it respond when the button was pressed.  The group that I worked with produced code to make the light on the board turn on when the button that we added to the board is pressed.  I’ll explain the basic concepts of what we did.

The important thing to know in either case is that the microcontroller uses memory registers for everything.  So, it is important to set up these registers correctly when starting the program, and read them correctly when checking to see what the pins are doing.

The first thing that must be done when creating a program like the one that we made is to ensure that the LED and button pins are set for input and output, respectively.  This is accomplished by setting the appropriate bits in the Data Direction Register for the port that they are located on.  This information can be found in the data sheet of the microcontroller.  In the assembly program, this is accomplished by using the sbi and cbi instructions to set or clear the bits in the register directly.  In the C program, bit math is used to OR the register with the desired bit directions for the pins in a small macro at the top of the program.

All that’s left to do is to have the main loop of the program wait for input from the button pin, and set the LED pin high when it sees that the button is pressed.  In the assembly program, the sbic instruction causes the program to branch and jump back to the beginning of the main loop if the button pin resolves to TRUE (not connected to ground) otherwise, it blinks the LED and then jumps back to the beginning of the main loop.  In the C program, there’s a macro that does bit math on the PORTA register to see if the pin that the button is attached to is NOT high because the button is pressed.

You can download the assembly program here.

You can download the C program here.

I also began to make a completely new board design of my own.  The idea is a two-player game called “Quick Draw” - there are three LEDs and two buttons.  When the LED in the middle of the board turns on, the player who presses their button to light their LED first wins.  Unfortunately, I was not able to start designing it until Sunday afternoon due to my sponsor week duties as well as my parents being in town for the weekend.  The Modela table was still unleveled (see everyone’s blogs who tried milling on Friday) and I did not know where the new sacrificial boards were kept, so I was unable to even get the board made by the time I gave up sometime in the wee hours in the morning.  Grr.

********************INCOMING MESSAGE FROM THE FUTURE********************

Hello.  This is David speaking to you from next week.  Do not be discouraged, past self.  In the future, you will finish the Quick Draw game pcb and successfully re-learn to program interrupts in C in order to get the game working.

I will allow people to download a .zip file of the schematic, circuit board, and firmware from the future using this link.  Take it easy on the traffic though; trans-temporal bandwidth isn’t cheap.

Oh yeah, and don’t go to the food truck for lunch on Tuesday.  Trust me.

**************************TRANSMISSION END******************************