void setup() {
  // put your setup code here, to run once:
  volatile char *dirf,*dirk;
  volatile char *outf,*outk;
  dirf=0x30;dirk=0x107;
  outf=0x31;outk=0x108;
  *dirf=0x01;*dirk=0x01;

  *outf=0x01;*outk=0x00; // cathode control "glow"
  //*outf=0x01;*outk=0x01; cathode control "not glow"

  //*outf=0x00;*outk=0x00; anode control "glow"
  //*outf=0x01;*outk=0x00; anode control "not glow"
}

void loop() {
  //the led will glow only when anode is 5v and cathode is 0v

}