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What is CPS2 XOR?

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5 replies to this topic

#1
Gryph

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I've seen this mentioned a couple of time and don't know what's so special about it. I know it deals with Capcom games but thats about it.

#2
taratata

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The XOR tables are a method of encryption used in CPS2 games.
XOR stands for eXclusive OR. This should mean something to those with a bit of experience in electronics or boolean algebra.
Anyway, each game has its own table, so to emulate the game, you have to figure out the table.
The tricky thing there is that these tables are stored in a S-RAM chip, making it very uneasy to read: as soon as you unplug the battery, all the information is lost (at least that's what they think at CPS2Shock).
From their website:

The CPS-2 game boards are protected by a system that uses encrypted program ROM's. We believe the key data for the decryption of these ROM's is stored in low power S-RAM located inside one of the onboard custom chips. When the game board is switched off or disconnected from the main board, these custom chips are supplied by a 3,6v lithium battery. The average life span of this battery is around five to six years. Once the voltage of this battery is below 2v, the stored encryption key will be lost. The condition of this battery is not measurable due to the fact that lithium batteries will hold their voltage almost constant until the end of their life.

They tried dumping it from working CPS2 boards, but from what they say, all attempts have failed.
I have no idea how they figure out these tables.

I hope that helped you to have an idea of what XOR tables are :D
If it's not clear (and I'm pretty sure it's not :( ) don't hesitate to ask more explainations on a particular point.
I'll help as much as I can :(

#3
Gryph

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Thanks for the info. It explained it somewhat :P

#4
Agozer

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Yeah, well...CPS2Shocks dudes (like Razoola) are real wizards when it comes to understanding CPS-2.

#5
Xeon

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in laymans terms, just consider them as essential files so you could play your CPS-2 ROMs on emulators. without them, your ROMs are useless.

#6
Tidus

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It=Without Them,CPS2 Emulation Will Not be Possible




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