INT 15,83 - Event Wait

	AH = 83h
	AL = 0	set interval
	   = 1	cancel interval (PS/2)
	CX,DX = number of microseconds to wait (976 µs resolution)
	ES:BX = pointer to memory flag (bit 7 is set
		when interval expires)
	        (granularity is 976 microseconds)


	on return:
	CF = 1 if function already busy
	AH = 80h for PC
	   = 86h for XT & AT


	- available on the AT (BIOS after 1/10/84) and PS/2's except 30
	- designed for use in simple multitasking