blink-5.c

#include <avr/io.h>
#include <avr/interrupt.h>

ISR (TIMER0_COMPB_vect)
{
  PORTD ^= 0x40;
}

int main (void)
{
  cli ();
  TCCR0B = (1 << CS01) | (1 << CS00);  /* Takt durch 64 dividieren */
  TIMSK0 = 1 << OCIE0B;  /* Interrupt einschalten */
  sei ();
  DDRD = 0xfd;   /* binär: 1111 1101 */
  PORTD = 0x40;  /* binär: 0100 0000 */
  while (1);
  return 0;
}