Int 2F Fn 5602  - Interlnk - Check If Port In Use                          [R]

   AX = 5602h
   DX = magic value FFFFh
   BL = instance number (00h=any, 01h=first loaded, etc.)
   CX = base port address of COM / LPT port to check

Return: (as for AL=00h if port in use for a redirected drive)

See Also: AX=5600h