Int 16 Fn FF9D  U - Pc Tools V8+ Cptask, Vsafe - ???                       [-]

   AX = FF9Dh
   ES:BX -> ??? word

Return: ???

Note:  if ES is non-zero, the word pointed at by ES:BX determines whether the
     ??? flag is cleared (word = 0000h) or set (word is nonzero).  The
     flag is always cleared if ES=0000h.