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Unprotect Sierra On-Line's Space Quest game. by Independent (IND)

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2 items
  • SIERRA.DAT
  • SIERRA.DOC
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        This procedure will enable you to unprotect Sierra On-Line's SPACE
        QUEST game.  The procedure is based on an unprotect procedure for
        KING'S QUEST III, by an unknown author.

        There are two files included in this ARC package:

                1.  SIERRA.DOC - This file
                2.  SIERRA.DAT - Supplementary file needed during DEBUG session.

        SIERRA.DAT was originally named KQ3MERG.DAT, but I've taken the
        liberty of renaming it, since it is usable in other Sierra games.

        The procedure is relatively simple:

        1) Put a blank, formatted diskette in drive B, and the Spacequest Disk
        #1 in drive A, then at the A> prompt, COPY *.* B:.  Then put Disk #1
        away - you won't need it anymore!

        2) Load DEBUG, making sure both SIERRA.COM (on the backup disk) and
        SIERRA.DAT (from this package) are both in the current path or on the
        default drive.

        3) Use DEBUG to patch SIERRA.COM.

                -N SIERRA.COM
                -L
                -R                            (Record value of CX register)
                -N SIERRA.DAT
                -L 141
                -E 395
                XXXX:0395 E8.90 52.90 02.90   (XXXX:03E1 for KING'S QUEST III)
                -N SIERRA.COM
                -R CX
                CX 0080
                :????                         (Enter value of CX you recorded)
                -W
                -Q

        4) That's all there is to it.  SPACEQUEST is now unprotected.

        This procedure will probably work with any Sierra game that uses the
        SIERRA.COM game loader.  To check, try the following DEBUG session:

                -N SIERRA.COM
                -D 100             (You will see a dump of the first part of the
                                                file.  If the version is 3.0, this patch
                                                should work.  If not, you can try, but there
                                                are no guarantees)
                -R                                      (Record the value of the CX register)
                -S 100 ???? E8 52 02    (Replace ???? with the value of the CX
                                                        register)

        You're looking for the E85202 string, which is the call to the
        protection scheme.  With luck, DEBUG will report only one find.
        Replace that location with the 395 in the E 395 command in the
        procedure above, and do everything else the same.  The idea is to NOP
        around the call.  SIERRA.DAT contains some code that is overlaid on a
        section of SIERRA.COM - I don't know how it works, but it does.

        Have fun!