INT 14 - COURIERS.COM - CHECK IF PORT BUSY
AH = 81h
AL = port number (1-4)
Return: AH = 00h port available
01h port exists but already in use
02h port nonexistent
Note:   COURIERS is a TSR utility by PC Magazine
SeeAlso: AH=8Dh

See also: 1483

1481 - COURIERS.COM - CHECK IF PORT BUSY