Function 83h	Event Wait			 (AT, XT/286, Convertible,
						  PS/2 except 25 & 30)
entry   AH      83h 
	AL      00h     to set interval 
		10h     to cancel 
	CX,DX   number of microseconds to wait (granularity is 976 microseconds) 
	ES:BX   pointer to memory flag (bit 7 is set when interval expires) 
		(pointer is to caller's memory) 
return  CF      set (1) if function already busy 
note	1) The function call returns immediately. If the function is
	   successful, bit 7 of the semaphore byte is set when the specified
	   interval has elapsed. The calling program is responsible for
	   clearing the semaphore before requesting this function.
	2) The actual duration of an event wait is always an integral multiple
	   of 976 microseconds. The CMOS date/clock ship interrupts are used to
	   implement this function.
	3) Use of this function allows programmed, hardware-independent delays
	   at a finer resolution than can be obtained through use of the MS-DOS
	   Get Time function Int\21f\2C which returns time in hundredths of a
	   second.
	4) See also Int\15f\86 which suspends the calling program for the
	   specified interval in milliseconds.
	5)