Hands On AVR

Overview

This wiki page is dedicated to AVR development with focus on the ATtiny13.

Memory

The ATtiny13 has two main memories:

Program memory is 1K Bytes. It's organized as 512x16 Bits, because all AVR instructions are 16 or 32 bits wide.

Data memory is 64 bytes of SRAM (internal memory) + 64 I/O Registers + 32 general purpose registers.

Furthermore there's electrically erasable programmable read-only memory (EEPROM) of 64 Bytes. Single bytes can be read and written.

I/O Ports

Individual I/O ports can be set as input or output. Each output can deliver 40mA.

The ATtiny13 has 6 I/O pins named: PB0, PB1, PB2, PB3, PB4 and PB5. Generally AVR ports are named Pxn, x is the letter of the port, n is the pin number.

All pins of PORTB of the attiny13 can be configured with only three registers:

• Data Register - PORTB - write values to port PBx / set internal pull-up of PBx
• Data Direction Register – DDRB - set PBx as input (0) or output (1).
• Port Input Pins – PINB - read values at port PBx

Notes:

• If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor is activated.
• The pin numbers don't correspond to the acutal hardware pin numbers, for example PB0 is located at hardware pin 5.
• All ports have also alternate functions (ADC, PWM, ..).

ArduinoISP

Arduino can be used as an In-system programming (ISP) interface for the ATtiny and ATmega microcontrollers.

Here are step-by-step instructions on how to program an attiny13 with an LED blinking program:

• On the Arduino, the ArduinoISP code must be running. Open the Arduino IDE -> examples -> ArduinoISP and write.
• Build the circuit as shown above. Pins are documented in the source code. Use a 470Ω resistor between PB4 (that's pin 3 on the attiny13) and the LED.
• Install AVR toolchain: Windows, Mac
• Compile this code:

/*
hello, LED!

attiny13 Pins:

1: RESET (Arduino 10)
2: NC (not connected)
3: R (470Ω) to LED to GND
4: GND (Arduino Gnd)
5: MOSI (Arduino 11)
6: MISO (Arduino 12)
7: SCK (Arduino 13)
8: VCC (Arduino 5V)

*/

#define F_CPU 9600000	// Define software reference clock for delay duration

#include <avr/io.h>
#include <util/delay.h>

#define LED PB4 // Define led output on PB4

uint16_t d; // delay variable

/**
 * delay
 *
 * @param ms duration in milliseconds
 *
 */
void delay_ms(uint16_t ms)
{
	for (uint16_t i = 0 ; i < ms ; i++) {
 		_delay_ms (1); // Loop delay
 	}
}

int main()
{
	d = 250; // delay time in ms
	DDRB |= (1 << LED); // Set direction to output for LED
	
	for (;;) {	// forever
		PORTB ^= (1 << LED);
		delay_ms(d);
	}
	return 0;
}

• run avrdude, make sure you choose the correct USB port and speed, i gave the program the name 'led.hex':

 avrdude -P COM9 -b 19200 -c avrisp -p t13 -U flash:w:led.hex:i

• enjoy the blinking LED!

High Voltage Fuse Resetter

If the fusebits are messed up, the AVR can be factory resetted. This can be done with "high-voltage serial programming". Here is a excellent project to reset attiny13/25/45/85 chips: hvsp fuse resetter

tips:

• The schema on the website seems to have bugs, i fixed them, check my copy File:Hvsp-fuse-resetter-schema.pdf.
• The 7x4 LED module can be found on ebay. If the display doesn't work, you probably have to comment out "#define _REVERSE" in the code, this switches common anode/common cathode of the display.

AVR

more on AVR soon.