void setup() {
  // put your setup code here, to run once:
  volatile char *dirf = (volatile char *)(0x30);
  volatile long i;
  *dirf = 0x01;
  while(1)
  {
    change();
    for(i=0; i<500000; i++);
  }
}

void change()
{
  volatile char *outf = (volatile char *)(0x31);
  *outf = *outf ^ 0x01;
}

void loop() {
  // put your main code here, to run repeatedly:

}