#define DDRB (*(volatile unsigned char *)(0x17 + 0x20))
#define PORTB (*(volatile unsigned char *)(0x18 + 0x20))

unsigned char *led;

void led_on ()
{
  PORTB = 0x00;
}

void led_off ()
{
  PORTB = 0xff;
}

int main ()
{
  int i;

  DDRB = 0xff;

  for(;;) {
    led_on();
    for(i = 0; i < 0xffff; i++);
    led_off();
    for(i = 0; i < 0xffff; i++);
  }
  
  return 0;
}