#include <avr/io.h>							//Deklarationen
#include <avr/signal.h>						//für Interrupt
#include <avr/interrupt.h>					//für Interrupt
#include <avr/delay.h>						//für Delay
//#ifndef F_CPU									//
//#define F_CPU 3686400UL						//für richtige Zeit
//#endif										//

volatile unsigned char  toggle=0;			//globale Variable
volatile unsigned int count=0;				//globale Variable

int main (void)
{

  DDRA = 0xFF;         //Ausgang PORTA
  PORTA = 0xFF;        //LED Aus

  // Timer 0 konfigurieren
  TCCR0A = (1<<WGM01); // CTC Modus
  TCCR0B |= (1<<CS01); // Prescaler 8
  // ((1000000/8)/1000) = 125
  OCR0A = 125-1;

  // Compare Interrupt erlauben
  TIMSK |= (1<<OCIE0A);

  // Global Interrupts aktivieren
  sei();


while(1)
{

ISR (TIMER0_COMPA_vect);
{
  count ++;

  if (count == 1000)  // alle 1000 ms LED toggeln
  {
    if (toggle == 0)
    {
      PORTA = 0b11111110;
      toggle = 1;
    }
    else
    {
      PORTA = 0b11111111;
      toggle = 0;
    }
    count = 0;
  }
}

}

return 0;
}