INT 15,80 - Device Open

	AH = 80h
	BX = device id
	CX = process id


	on return:
	CF = 0 if successful
	   = 1 if error
	AH = 80h for PC & PCjr
	   = 86h for XT (BIOS after 11/8/82)


	- available on the AT, XT 286, PS/2 and XT with BIOS after 11/8/82
	- designed for use in simple multitasking