enum : uint8_t {LSB, MSB};
union intByte {
  uint16_t uint;
  uint8_t byte[2];
};

void setup() {
  // put your setup code here, to run once:
  DDRB |= 0b00111111;
  DDRD |= 0b11110000;
}

void loop() {
  // put your main code here, to run repeatedly:
  static intByte potVal;
  potVal.uint = 16 * analogRead(A0);
  PORTB = PORTB & 0b11000000 | potVal.byte[MSB];
  PORTD = PORTD & 0b00001111 | potVal.byte[LSB];
  delay(50);
}