MODE DETECTION


            It is possible to write a program or library that can run in
            either real or protected mode.  This function is supplied so
            that bimodal  code can  detect at  run time  whether  it  is
            running under  protected mode.    Code  that  only  runs  in
            protected mode does not need to perform this test.

            To Call

                 AX = 1686h
                 Execute an Int 2Fh (not an Int 31h)

            Returns

                 If executing in protected mode under DPMI:
                 AX = 0

                 If executing in real mode or not under DPMI then:
                 AX != 0

            Programmer's Notes

                 o    This call  will return  AX = 0  when the caller is
                      running in protected mode.  It will return AX non-
                      zero even  when running  under  environments  that
                      support DPMI  if the  caller is  in real  (virtual
                      8086) mode.