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From: dj@ctron.com (DJ Delorie)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Protected mode/Real mode switching
Message-ID: <1426@balrog.ctron.com>
Date: 15 Apr 91 19:50:41 GMT
References: <1991Apr15.160333.8107@msuinfo.cl.msu.edu>
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In article <1991Apr15.160333.8107@msuinfo.cl.msu.edu>, mackay@eecae.ee.msu.edu (James F. MacKay) writes:
> Can someone explain to me how to write a program that is capable
> of running normally in protected mode, but can switch into real
> mode for DOS calls?  MS C and/or ASM preferred.

First, get Intel's programmers reference/guide/etc for the appropriate
processor.  Last I recall, there's an intro, guide, reference, and
system software guide.

Second, guess heavily.  This doesn't seem to be a popular subject at
your local bookstore.

Switching back to real mode is a big problem on 286's, as the chip
can't do it by itself.  386's have an instruction for it.

VVVV This part of the response is for 80386 protected mode only VVVV

If you can learn by example, and have FTP available, download my gcc
port from grape.ecs.clarkson.edu via anonymous FTP to pub/msdos/djgcc.
The sources for the 386 extender (go32) are included.  It should be
posted to comp.binaries.ibm.pc when it gets to the head of the queue.


DJ
dj@ctron.com