INT 15H 80H: Device Open
Expects: AH 80H
BX device ID
CX process ID
CF NC (0) (clear the Carry Flag before when invoking this fn)
Returns: AX 0080H
Info: This service is designed to be intercepted by a multitasking
operating system. It would be used, along with INT 15H fns 81H
and 82H to avoid device conflicts.
When unintercepted, the BIOS simply sets AH to 0 and clears CF.
See Also: INT 15H (extended AT services)
BIOS Data Area