INT 15,20 - PRINT.COM Critical Region Flag (undocumented DOS 3.x+)

AH = 20h

AL = 00 disable user critical region flag

= 01 enable user critical region flag

ES:BX = pointer to user critical region flag byte (AH = 1)

returns nothing

- provides PRINT.COM with the address of a byte to increment on

entry to DOS functions

- see ~bibliography~ reference for "Undocumented DOS"