Int FD  - Tfpcx - Installation Check                                       [S]

   AH = function (also see separate entries below)
Program: TFPCX is an interface between modem and terminal program for packet-
     radio communications

Notes: the installation check consists of testing for the string "N5NX" three
     bytes beyond the interrupt handler; INT FD is the default, but may
     be changed, so the full installation check consists of scanning
     for the signature
   TFPCX returns AX=FFFFh on any unsupported function call

See Also: AH=01h,AH=03h,AH=FEh