Int 14 Fn 81  - Couriers.com - Check If Port Busy                          [S]

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

Return: AH = 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