Int 11 Fn FFFE  - Back&forth (before V1.62) API                            [T]

   AX = FFFEh
   CX = FFFEh
   BX = function
       00h installation check

       Return: AX = 0001h BNFHIGH and BNFLOW both loaded
              = 0003h only BNFHIGH loaded
              else neither loaded
       01h ???

       Return: DX:AX -> ???
       02h ???
       03h ???
       04h ???
       05h ??? switches current PSP segment and stack if BNFLOW has not
           yet announced itself installed
       06h ???

       Return: AX = ???

See Also: INT 12/AX=FFFEh
Index: installation check;BACK&FORTH