Int 14/AH=81h

AH = 81h
AL = port number (1-4)

Return:
AH = status
00h port available
01h port exists but already in use
02h port nonexistent

Program: COURIERS is a TSR utility by PC Magazine

See Also: AH=83h - AH=8Dh

Category: Serial I/O - Int 14h - C