Getting started

I recently started to play more seriously with the ATMEGA8 microcontroller from atmel. The same device runs on the Arduino boards. Since I like doing things from scratch, I prefer to play with the bare microcontroller. In this blog I'll share my experiences. Another intention is the following: The ATMEGA8 device is very well documented in the datasheet. But reading tens of pages to know how to enable a timer or the ADC is tedious, especially for beginners. I intend to go through different features of the ATMEGA8 and provide minimal programs to enable and use them.

In order to get started, a programmer is necessary. That is not the case if you have an Arduino board.
I own a programmer from Tuxgraphics.org. Their webpage contains lots of ATMEGA related information and electronics in general. The programmer I bought was a kit that I needed to solder. Also the firmware wasn't installed on the device. But one can load the firmware to it without having a programmer. I it is very interesting to see how it works.

However, building a kit is tedious if you just want to get started with playing. Tuxgraphics.org offers assembled programmers as well. But if you are short on money, you can find lots of (incredibly) cheap offers for programmers on ebay. I recently bought an USBasp programmer from a Chinese manufacturer for about 4 EURO. I donated a bit of money to the inventor of hard and firmware. I think it is fair and it supports the open hardware and open source movement.

All you need in addition is a breadboard, one ATMEGA8 controller in a DIP (dual in-line) package that you can place on the board and some wires plus all components you want to control (such as an LED and a ~500 ohms resistor). No soldering required at all.

The "hello world" in microcontroller programming is a blinking LED. I will show how to do this in this first post.

My programmer has a 10pin adapter. The basic wiring is like this:

The LED is connected from VCC through a 220 ohm resistor to the PD0 pin of the controller.

If the hardware is set up, the controller can be programmed with a firmware. To create the firmware, I write programs in C. To get them compiled and copied to the controller I need C-compiler and a programming software. I use Linux and the packages "avr-gcc" (compiler) "avrdude" (programming software).

The program that makes the LED blink (blink.c) looks like this:

#include <avr/io.h>
#define F_CPU 1000000UL  // 1 MHz
#include <util/delay.h>

int main(void)
{
 DDRD = 1;
 while(1)
 {
  _delay_ms(200);
  PORTD ^= 1;
 }
}

To get this program running on the microcontroller, three steps are neede:

1. Compiling

avr-gcc -mmcu=atmega8 -Os blink.c

The flag -mmcu=atmega8 informs the compiler about the target arcitecture. -Os optimizes for size of the resulting program.

The result of this call is a file "a.out" which has to be converted to a .hex file that can be copied to the program memory of the controller. 

2. Converting

avr-objcopy -O ihex a.out blink.hex

The flag -O ihex specifies the desired output format and the resulting file is "blink.hex"

3. Loading

avrdude -p m8 -c usbasp -U flash:w:blink.hex

copies the program to the controller, where -p m8 specifies the target device (or part), -c usbasp is my programmer and -U flash:w:blink.hex specifies the program data.

If the last command doesn't work you may not have access to the USB device. The simplest way to solve this is to become root before loading the firmware.

If a LED is connected, it should start blinking now. If everything is working, the door is open to the fascinating world of embedded programming!