16 bit Timer rasst davon..

#define F_CPU  16000000UL

#include <avr/io.h>

#include <avr/interrupt.h>

int main(void)

{

  uint16_t Timer = (F_CPU/1024) -1;

  TCCR3A = (1<<WGM31);      //CTC Mode

  TCCR3B = (1<<CS32) | (1<<CS30);    //prescaler 1024

  OCR3AH = (Timer>>8);      //t = 1s

  OCR3AL = Timer;

  TIMSK3 |= (1<<OCIE3A);    

  sei();

  DDRL = 0xFF;

    while(1)

    {

        //Blablabla

    }    

}

  ISR(TIMER3_COMPA_vect)

  {

    PORTL ^= (1<<PL0);

  }