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From: simrin@mis.ucsf.edu (Steve Simrin)
Newsgroups: comp.sys.ibm.pc
Subject: Re: INT 21H AH=50H/51H under DOS 2.11
Message-ID: <1079@ucsfcca.ucsf.edu>
Date: Mon, 16-Nov-87 15:14:33 EST
Article-I.D.: ucsfcca.1079
Posted: Mon Nov 16 15:14:33 1987
Date-Received: Wed, 18-Nov-87 06:27:16 EST
References: <310@apex.UUCP>
Sender: root@cca.ucsf.edu
Reply-To: simrin@mis.ucsf.edu.UUCP (Steve Simrin)
Organization: UCSF Medical Information Sciences
Lines: 7
Keywords: Functions 50h/51h can be used in a memory resident program under DOS 2.xx IF the critical error flag is set. Setting the flag forces DOS to use the correct internal stack. If the flag is clear, DOS uses the wrong stack and the system bombs.
Approved: rces DOS to use the correct internal stack. If the flag is clear, DOS uses the wrong stack and the system bombs.
Summary: functions 50h/51h and critical error flag


 The address of the critical error flag is obtained using function 5Dh.
 On the call, AL contains a value of 06h. On return, DS:SI points to the
 critical error flag.

 Be forewarned that this is all undocumented but it is used by many TSR
 programmers.