#define MS *5

   outportb(0x43, 0x26);  // bit 7,6 = (00) timer counter 0
                          // bit 5,4 = (10) write MSB only
                          // bit 3-1 = (011) generate square wave
                          // bit 0 = (0) binary counter
                          // prep PIT, interrupts when counter decrements to 0
   outportb(0x40, 5 MS); // set MSB of timer count  (max 51 ms)