void setup() {
  volatile char *ddra;
  ddra = 0x21;
  *ddra = 0xff;
  volatile char *ddrb;
  ddrb = 0x24;
  *ddrb= 0xff;
}

void loop() {
  // put your main code here, to run repeatedly: 
  volatile char *outa = (char*)0x22;
  volatile char *outb=(char*)0x25;
  volatile long i;
  unsigned char seg_code[10] = {
    0x3F, // 0
    0x06, // 1
    0x5B, // 2
    0x4F, // 3
    0x66, // 4
    0x6D, // 5
    0x7D, // 6
    0x07, // 7
    0x7F, // 8
    0x6F  // 9
  };
  for (int tens = 0; tens <= 9; tens++) {         // Tens place
    for (int ones = 0; ones <= 9; ones++) {       // Ones place
      *outb = seg_code[tens];                     // Display tens digit
      *outa = seg_code[ones];                     // Display ones digit

      // ~1 second delay
      for (i = 0; i < 1000000; i++);
    }
  }
  
  
}