void setup() {
  volatile char *ddra;
  volatile char *ddrb;
  
  ddra = (char*)0x21;   // Data Direction Register for PORTA
  ddrb = (char*)0x24;   // Data Direction Register for PORTB

  *ddra = 0xFF;         // PORTA as output (integer part)
  *ddrb = 0xFF;         // PORTB as output (decimal part)
}

void loop() {
  volatile char *outa = (char*)0x22;  // Output register for PORTA
  volatile char *outb = (char*)0x25;  // Output register for PORTB
  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
  };
  unsigned char seg_code1[10] = {
    0xBF, // 0.
    0x86, // 1.
    0xDB, // 2.
    0xCF, // 3.
    0xE6, // 4.
    0xED, // 5.
    0xFD, // 6.
    0x87, // 7.
    0xFF, // 8.
    0xEF  // 9.
  };

  // Display from 0.0 to 9.9
  for (int tens = 0; tens <= 9; tens++) {
    *outb = seg_code1[tens];        // Integer part on PORTA
    for (int ones = 0; ones <= 9; ones++) {
      *outa = seg_code[ones];      // Decimal part on PORTB
      
      // Simulated 0.5 second delay
      for (i = 0; i < 500000; i++);
    }
  }
}