int LED_utrip = 500; // utripanje na 500 ms
unsigned long changeTime;
bool m = HIGH;

void setup() {
  DDRD = 0xff; // na PORT D priključi LED
  //changeTime = millis();
}

void loop() {

  if((millis() - changeTime) > LED_utrip){
    m = !m;
    changeTime = millis();
  }

  if (m == HIGH){
    PORTD = (1<<PD0) | (1<<PD3) | (1<<PD6); // ali PORTD = 0b01001001; ali PORTD = 0x49
  }
  if (m == LOW){
    PORTD  = (0<<PD0) | (0<<PD3) | (0<<PD6); // ali PORTD = 0x00;
  }

}