int main()
{
  // set pa0, pa1 and pa3 as outputs
  DDRA = 0x0b; // 0b 0000 1011

  // set pa0 to low level
  PORTA = 0x00; // 0b 0000 0000

  // set pa1 and pa3 to high level
  PORTA = 0x0a; // 0b 0000 1010
}