RTC - Tutor - Part 1



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 < Preface >

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   This series is aimed to help you de-protect certain programs to make back-up

copies of the programs hereafter, and only for that purpose. The authors take

no responsibility for an(y) illegal cop(y)(ies) made by the end user of this

information, nor any damage to programs, hardware, or any other physical damage

done by the use of the information hereafter.



   The authors urge you to attempt to make nibble copies of the program before

attempting any modification to the program. The techniques described in this

series may not work on all versions of the program. In most cases there are

many other ways to de-protect the program (such as nibble counts) and if any of

you know of a better way please let us know.



   More advanced crackers or programmers who know machine language pretty well

might want to skip the text and just read the => prompts. The -> prompt

indicates a place in the instructions where you may not need to go any further.



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This weeks topic: Xerox educational games



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Xerox is known for their excelence in education games such as the Stickybear

series, Chivalry, Fat City, Pic Builder, and others. The protection on these

games is fairly standard, a single nibble count. To modify the nibble count so

it does not function, we need a sector editor. Inspector is the most popular,

although the sector editors in Nibbles Away ][ and Copy ][+ both are fine. Of

course, we suggest you make a back-up of the program before modifing any data.



=> Read Track 2, Sector 6

=> Change byte $00 from $A9 to $60

=> Write Track 2, Sector 6 back to disk.



Notes: You just disabled the nibble count. The start of the routine was at, of

course, Track 2, Sector 6. The routine was in machine, so $A9 (the first byte

of the routine) stood for LDA (LoaD Accumulator). By replacing it with $60

(which stands for RTS, or ReTurn from Subroutine) we returned to the main

program without doing the nibble count. This will not work for ALL of the Xerox

software, such as Stickybear Bop and Pic Builder, but will work for almost all

of it.



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