void setup() {
  // put your setup code here, to run once:
  volatile char *dirf,*dirk,*dirc,*dira;
  dirf=0x30;dirk=0x107;dira=0x21;dirc=0x27;
  *dirf=0x0f;
  *dirk=0x00;
  *dira=0x0f;
  *dirc=0x0f;

}

void loop() {
volatile  char *outf,*ink,*outa,*outc;
outf=0x31;outc=0x28;outa=0x22;ink=0x106;
volatile long i;
for(i-0;i<4;i++)
{
  *outf=1<<i;
  *outa=*ink;
  if(*ink!=0)
  {
    *outc=1<<i;
    for(volatile long j =0;j<100000;j++);
    *outc=0;
    }
  }
  

}