void setup() {
  DDRD  = 0B11111111; // ADAT IRÁNY BEÁLL.
} 

void loop() {
  
  for (int i = 1; i < 255; i = i * 2) {
   PORTD = i;
   delay (100);
  }

   for (int i = 128; i > 0; i = i / 2) {
   PORTD = i;
   delay (100);
  }
}