Function 00h    Read System Time Counter
entry   AH      00h 
return  CX      high word of clock count 
	DX      low word of clock count  
	AL      00h if clock was read or written (via AH=0,1) within the current 
		24-hour period. Otherwise, AL is non-zero
 
note 1) The clock ticks are incremented by timer interrupt at 18.2065 times
	per second or 54.9254milliseconds/count. Therefore:  
		counts per second = 18      (12h) 
		counts per minute = 1092    (444h) 
		counts per hour   = 65543   (10011h) 
		counts per day    = 1573040 (1800B0h) 
     2) Through an incredible coincidence, the low word rolls over into the
	high word once every 3599.54 seconds which is allmost exactly once an
	hour (3600 seconds). So the high word is the number of hours and the
	low word is the number of minutes * 1092 or seconds * 18.2.
     3) counter is zeroed when system is rebooted