Int 21 Fn FF  UP - Rational Systems DOS/4gw - API                          [E]

   AH = FFh
   DH = function (00h-17h) (see also separate entries below)
   DL = subfunction or argument

Return: CF clear if valid function number
       AX = status???
   CF set if invalid function

See Also: INT 15/AX=BFDCh