Int 2F Fn 1681  - MS Windows 3+ - Begin Critical Section                   [W]

   AX = 1681h

Notes: used to prevent a task switch from occurring
   should be followed by an INT 2F/AX=1682h call as soon as possible
   nested calls are allowed, and must be followed by an appropriate number
     of "end critical section" calls
   not supported in Windows/386 2.x. Get INDOS flag with INT 21/AH=34h and
     increment by hand.

See Also: AX=1682h,INT 15/AX=101Bh,INT 21/AH=34h