// https://wokwi.com/projects/351674089577906776
// https://forum.arduino.cc/t/struct-of-pines/1067726

// 13, 10, 7 and 3

void setup() {

  Serial.begin(115200);
  Serial.println("hello world.\n");

  pinMode(13 , OUTPUT);
  pinMode(10 , OUTPUT);
  pinMode(7 , OUTPUT);
  pinMode(3 , OUTPUT);
}

void loop()
{
  static unsigned char tt;

  set4Bits(tt);
  delay(474);

  tt++;
}

// place theBits into output pins 13, 10, 7 and 3

void set4Bits(unsigned char theBits)
{
  PORTB = (PORTB & 0xdb) | ((theBits & 0x8) << 2) | (theBits & 0x4);
  PORTD = (PORTB & 0x77) | ((theBits & 0x2) << 6) | ((theBits & 0x1) << 3);
}