Re: A little trick went horribly wrong (removing crackscreen)

[Chris <junk@trash.org>]

OK, I found my notes.  The code to be patched is at the 9th sector of
the file, byte $3C.  Change 20 00 60 (JSR $6000) to EA EA EA.  This
will disable the checksum routine.

Oddly, some emulators (Applewin) are not affected by the checksum
routine.  The game will run with altered text and the checksum still
enabled.


On Sat, 01 Jan 2005 13:47:23 GMT, Moll
<Mollyzkoubou@Spam.BettyKate.Spam.Spam.Spam.Dosius.Com> wrote:

>Chris wrote:
>> I attempted the same edit to the cracked Ms. Pac-Man many years ago.
>> There is a checksum performed on the title text which will cause a
>> crash if altered.
>> 
>> As I recall, there is a jmp (or jsr) at the start of the file to the
>> checksum routine at the end of the file.  Bypassing the checksum
>> routine simply involved NOP'ing (EA EA EA) the initial jump.  Then the
>> title text could be altered safely.
>> 
>> I still have the patch written down and archived away with my notes if
>> you're interested.  Although it shouldn't be too difficult to find it
>> with the info I just gave.
>
>The first instruction is 17FD:JMP $2000
>
>Skipping / commenting out that code causes a different failure.
>
>I'd be interested in this patch if you can find it. (Thanks) ;)
>
>Moll.