#define NUM_DIGITS 8

unsigned char __idata __at(0x60) my_num[NUM_DIGITS];

void inc_my_num()
{
    unsigned char __idata *p = my_num;
    unsigned char i = NUM_DIGITS;

    do
    {
        (*p)++;
        if( 10 == *p )
           *p = 0;
        else
           break;

        p++;
    } while (--i)