INT 15,86 - Elapsed Time Wait (AT and PS/2)

	AH = 86h
	CX,DX = number of microseconds to wait (976 µs resolution)

	on return:
	CF = set if error (PC,PCjr,XT)
	   = set if wait in progress
	   = clear if successful wait
	AH = 80h for PC and PCjr
	   = 86h for XT

	- AT and PS/2 only for system timing
	- not designed for user application usage