[PIC] PIC 18f4520 TMR0L , need setting for OPTION_REG

#include "Display_utils.h"

unsigned short shifter, portd_index;
unsigned int   digit, number;
unsigned short portd_array[4];

void interrupt() {
  PORTA = 0;                             // Turn off all 7seg displays
  PORTD = portd_array[portd_index];      // bring appropriate value to PORTD
  PORTA = shifter;                       // turn on appropriate 7seg. display

  // move shifter to next digit
  shifter <<= 1;
  if (shifter > 8u)
    shifter = 1;

  // increment portd_index
  portd_index++ ;
  if (portd_index > 3u)
    portd_index = 0;                     // turn on 1st, turn off 2nd 7seg.

  TMR0L   =   0;                          // reset TIMER0 value
  INTCON = 0x20;                         // Clear T0IF
}//~

void main() {
  //ANSEL       =    0;                    // Set AN pins to Digital I/O
  //ANSELH      =    0;
  OPTION_REG  = 0x80;                    // Timer0 settings
  digit       =    0;
  portd_index =    0;
  shifter     =    1;
  TMR0L        =    0;
  INTCON      = 0xA0;                    // Enable GIE, T0IE
  PORTA       =    0;
  TRISA       =    0;                    // Set PORTA as output
  PORTD       =    0;
  TRISD       =    0;                    // Set PORTD as output

  number          =   6789;              // some initial value
  do {
    digit = number / 1000u ;             // extract thousands digit
    portd_array[3] = mask(digit);        // and store it to PORTD array
    digit = (number / 100u) % 10u;       // extract hundreds digit
    portd_array[2] = mask(digit);        // and store it to PORTD array
    digit = (number / 10u) % 10u;        // extract tens digit
    portd_array[1] = mask(digit);        // and store it to PORTD array
    digit = number % 10u;                // extract ones digit
    portd_array[0] = mask(digit);        // and store it to PORTD array

    Delay_ms(1000);                      // one second delay

    number++ ;                           // increment number
    if (number > 9999u)
      number = 0;

  } while(1);                            // endless loop
}