Int 15 Fn 2001  U - DOS 3+ Print.com - Set Critical Region Flag            [c]

   AX = 2001h
   ES:BX -> byte which is to be incremented while in a DOS call
Desc:  specify a user flag which PRINT should set to let an interested
     application know it is in a critical region

Note:  also supported by PC Network v1.00 RECEIVER.COM

See Also: AX=2000h