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| From: Marko_Mäkelä
Date: 1998-05-17
Subject: Re: Tapes!
|
On Sun, 17 May 1998, Martijn van Buul wrote:
> Hmm.. Hmm.. I tried to crack one of my tape games this morning (this
> thread made me interested ;) but I'm having a hard time with this one.
> According to the tapeheader, the loader loads from $020F (which is the
> BASIC/ASSEMBLY working area). However, I just don't seem to be able
> to load that darn thing at another location (like $120F).
Just type L in TEDMON and press STOP when the FOUND message appears on the screen. Then change the loading address in the tape buffer ($33c or something) and continue loading by replicating the necessary code from the ROM in RAM. Sorry, I don't remember details, but I successfully copied some tape games a couple of months ago.
There was one turbo loader (maybe by Anirog) that was very difficult, and I gave up. Part of the loader code will be in the tape buffer, and the rest will be loaded to $2xx, so that it will overwrite the beginning of the tape buffer. The program will autostart, and the program starts with a loop that uses the undocumented DEC+CMP instruction to decrypt the rest of the program. It depends on the CPU register values set by the ROM routines. If I had had more time and a blank tape, I would have written a program that is equally big and ends in the same bytes, but stores the CPU registers when started.
> I guess I'll have to dissassemble the C64 SETLFS in order to be sure,
> but that involves a serious rearangement of my desk :)
The SETLFS and SETNAM routines just store A, X and Y to some zero page locations and exit.
Marko
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