AVRFreaks.net

#define F_CPU 1000000
#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
#include "hardware.h"

//definitions
void start_interrupt(void);//init
int main(void);

int main(){
   DDRD=0x7F;//enable lights
   DDRB=0x3F;
   start_interrupt();
   for(;;){
      _delay_ms(250);//delay to show lights
      PORTB=0x00;//clear all
      PORTD=0x00;
   }
   return 0;
}

void start_interrupt(){
   TCCR0A|=(1<<WGM01);//set to CTC mode
   TCCR0B|=(1<<CS01);//set prescaler to 1/8
   OCR0B=125;//interrupt every 1/1000th of a second
   TIMSK|=(1<<OCIE0B);//enable compare interrupt B
   sei();//enable interrupts
}

ISR(TIMER0_COMPB_vect){//compare interrupt B
   PORTB|=(1<<L2);//enable 2nd layer
   PORTD|=(1<<A5);//enable middle led
}

/*
 * hardware.h hardware specific information
 */
#ifndef _HARDWARE_
#define _HARDWARE_

//layers
#define L1   4 //PORTB
#define L2   3
#define L3   2
//anodes
#define A1   0 //PORTD
#define A2   1
#define A3   2
#define A4   3
#define A5   4
#define A6   5
#define A7   6
#define A8   0 //PORTB
#define A9   1

#endif