Ghostbusters (Activision, 1984)

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Chase the ghosts around the city. Use tanks to save people from being killed. The game includes a nice voice digit!


DISK STRUCTURE
It is a 16-sector DOS 3.3 disk with the following markers:
- All tracks: D5 AA 96 DE AA / D5 AA AD DE AA
- Track $01: D5 AA 96 DE AB / D5 AA AD DE AA
- Track $12: D5 AA 96 DE BC / D5 AA AD DE AA
- Track $13: D5 AA 96 DE CD / D5 AA AD DE AA


PROTECTION TYPE
The markers in italics are read and stored in ZP $04. The tracks are read by the loader at $4F00 (T0/SA). They are then used by the protection routine at $5000 (T0/SB) to decode the data loaded from the protected tracks.


DISK COPY
- Launch Advanced Demuffin
- Go to the monitor
- B942: 18
- CTRL-Y
- Copy the disk

Boot the disk... Grrr, it displays the intro page then hangs...


PROTECTION REMOVAL
Once a protected track is loaded, the marker value at $04 is stored in the following ZP addresses:
- Track $01 : $04 => $00 for marker $AB
- Track $12 : $04 => $02 for marker $BC
- Track $13 : $04 => $03 for marker $CD

Let's change the loader code on T0/SA ($4F00):
- Launch Disk Fixer
- Read T0/SA
- T0/SA/52: A5 04 85 01 => A9 BC 85 01
- T0/SA/59: A5 04 85 02 => A9 CD 85 02
- T0/SA/AA: A5 04 85 00 => A9 AB 85 00
- Save the sector back to disk


Boot the disk and enjoy...

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