void setup() {
  DDRD = 0xff; //0b11111111 ali 255- smerni register, port D 

}

void loop() {
  // PORTD = 255; // 0xff

  PORTD = (1<<PD3) | (1<<PD2) | (1<<PD1); // port 0 doesn't light up cuz it ain't included
  delay(500);
  PORTD = (~(1<<PD3)) | (~(1<<PD2)) | (~(1<<PD1));
  // PORTD = 0 / 0x00;
  delay(500);
}