gistfile1.c

// interrupt service routine to handle all interrupts
void interrupt main_isr(void) {
    // if Timer 0's interrupt flag has been raised
    if (TMR0IF) {
        // increment the millisecond counter
        milliseconds++;
        // set the Timer 0 value to 65536 - 2000 = 63536
        TMR0 = 63536;
        // lower the interrupt flag
        TMR0IF = 0;
    }
}