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1991-03-20
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There are five 'versions' of the assembly source to switch the computer
(x286,x386,x486) into protected mode.
The only version that I know works correctly is PROT4.ASM
Included is a compiled version of PROT4.ASM (prot4.com) and
liting and cross-reference to boot.
All it does is reverse the video to a very ugly color. Clear
the screen (CLS) to get rid of it.
PROT1.ASM
This version was taken from the book...
"Inside the 80286" by Ed Strauss ISBN 0-89303-582-3
This version is targeted for 'burn in' into EPROMs.
Never tried it, don't have EPROMs or EPROM burner.
PROT2.ASM
This version was taken from the same book as above.
Unknown why it never worked.
PROT3.ASM
Incomplete listing of another method, ignore this file, but
included because it contains useful macros.
PROT4.ASM
This is the ONLY working version. Unknown source.
PROT5.ASM
Same as PROT4.ASM except that the gating of address line 20
is performed differently, and for some reason, does NOT work on
80286 processors (I don't know why this is so).
If nothing else, this may provide an experimental base to learn more
about protected mode programming.
I do not claim that this will work on EVERY machine. It is largly
experimental, although your machine shouldn't get 'wrecked'.
ALSO!!!
The absolutly best book to get is
"Dr. Dobb's ToolBook of 80286/80386 Programming"
by Phillip Robinson ISBN 0-934375-42-9
This book has a PASCAL (!) source on going into protected mode.
The file PROTM1.PAS is an excerpt of that text.
(I would have the whole thing, but I did not finish typing it yet!)
Or, you can get the source code to all the protected mode programs
in the Dr Dobb's book by calling
1-800-533-4372
1-800-356-2002 (in CA)
ask for item #54-2
Send $20 (+ CA Sales tax if applicable) to
M&T Books
501 Galveston Drive
Redwood City, CA 94063
Again, Item #54-2 (they take VISA/MC/AMEX with # and Exp Date)
Checks payable to M&T Books
Note that the source code includes protected mode interfaces for Windows,
UNIX, OS/2 and MS-DOS. These programs range from the simple stuff to
task management and exception handling. Also included is protected mode
co-processor programming and i82786 graphics processor programming.
It's a big book (700+ pages), highly recommended.