void sleep(int ms)
{
    int i;
    for(i=0;i<ms;i++)
    {
        TH0 = 0xF9;    //higher nibble timer 0
        TL0 = 0xFB;    //lower
        TMOD = 0x01;   //set mode 1 (16bit, set TF0 to 1 on overflow)
        TR0 = 1;       //start
        while(TF0!=1); 
        TR0 = 0;       //stop
        TF0 = 0;     
    }
}