Description
Preamble
This lab is intended to introduce you to the Arduino environment and get you started
writing AVR assembly. We’ll be using a mix of inline assembly and Processing code in the
Arduino IDE. For this lab, and all upcoming AVR labs, you may work in groups of 1-3 people.
Lab Description
First thing’s first, download and install the Arduino IDE:
https://www.arduino.cc/en/main/software
As of this writing, the latest version is 1.8.12. Just get the latest version for your platform
from the above website.
0) Start by trying out some of the sample programs that come with the Arduino software.
They are all written in the Processing language. We’ll be using Processing for some
utilities like delay() and Serial.print() in the spirit of keeping things fun instead
of tedious.
The sample programs can be found under File->Examples. Explore, try out some of the
simpler ones, make sure your board is connected and working properly. The Arduino
software should work out of the box without any trouble.
Examples->Basics->Blink is a nice one to start with. It simply blinks an LED periodically
on the board. If this works, you’re good to go.
1) Now for the actual lab assignment. Starting with the Blink example as a template, we’re
going to convert the Processing statements into inline AVR assembly. Inline assembly
allows us to mix Processing code and assembly in the same program while remaining in
the Arduino IDE. Below is the same Blink program, but with pinMode() and
digitalWrite() function calls replaced with inline assembly. Try this out on your own
board. The LED should blink as before.
Notice we’ve kept the delay() function as-is. This is a handy part of inline assembly.
Rather than making you implement your own delay loop, we’ll just make use of the high
level function call.
void setup() {
asm(“sbi 0x04, 5”);
asm(“rjmp start”);
}
void loop()
{
asm(” start: “);
asm(” sbi 0x05, 5 “);
delay(200);
asm(” cbi 0x05, 5 “);
delay(200);
asm(” rjmp start “);
}
Inline assembly instructions are passed as strings to the asm() function. This is
annoying, but worth it for the added benefit of being able to develop in the Arduino IDE.
Look up the instructions sbi and cbi in the instruction set to see what they do.
Additionally, look up the registers at address 0x04 and 0x05 to see what bits we’re
setting and clearing.
2) The above program blinks an LED built into the Arduino board. That LED is connected to
PORTB pin 5. Using the data sheet and the Arduino pinout (can also be found in the
slides), determine the corresponding output port on the UNO. Connect a separate LED
to this pin using your breadboard. Use a 1k-ohm resistor between the positive LED wire
and the port on the UNO. Connect the other end of the LED to one of the ground (GND)
ports. Without changing any of your code or even turning your Arduino off, the LED
should blink just like the one on the board.
3) The 7-segment display that came with your kit is nothing more than a set of LEDs, each
of which can be connected to an output pin on the Arduino. Here, CC means common
cathode. The cathode is connected to GND, and each of the pins a-g connect to an
output port on the Arduino (through a 1k-ohm resistor, as before). On your breadboard,
connect each of the LEDs a-g to ports PD0-PD6 (you can ignore DP).
4) Once the 7-segment display is connected, modify your assembly program to blink the
number ‘3’ on the display. Use inline assembly for this! You’ll have to use the data sheet
to determine the corresponding addresses of pins PD0-PD6.
5) Finally, modify your program to not just blink the number 3, but rather cycle through
the numbers 0-9 and then loop back again at a rate of one increment per second
(delay(1000)). You’re not using any sort of addition for this – Just set or clear the
appropriate bits for each number. Don’t forget to set the appropriate bits in the data
direction register in setup() as well!
Submission
Labs are to be submitted in groups of 1-3! If working in a group, only one person should
submit. Clearly indicate in the submission the names of all group members. Submit the
following files under Lab #4 on D2L:
• A picture of your UNO and breadboard with the 7-Segment display. You don’t have
to include your face or anything like that, I just want proof that you physically wired
up the 7-segment display.
• Your source code for question 5 as a plain text (.txt) or assembly source (.asm) file.
I will be testing your submission on my own UNO with the display wired up in the same
manner. It’s critical that you’re using the correct pins indicated in the lab, as that’s the
configuration I’ll be testing on.
