There is no encryption going on, on cps1 games. Not a single line of it. The fact is that the ppu2 on the c board is able to use custom (understand other than e default ones) hardware adress registers.
When the battery dies those parameters are lost. Since the games have been coded with them in mind, when the game code ask for display the graphic layers, the ppu 2 is unable to recognize them.
In order to make the game working again, you need to patch all the hardware adresses related to layers enable disable words, patch the ctrl video register, multply protection, prirority masks , etc etc there is even a ppu2 (read cps-b-21-10014) hardware check which is by the way not present on all games.
The worse thing is that the games someof tem are doing XORing on the hardware layers values, so if you patch them, you need to modify the xor routines which are npthing more han checksums protection.
Knights of the round has 19 checksums buried inside it code, and slam masters has 67 checksums all in all.
Encryption only applies to cps-2.
And the c board hardware patch is needed to force the ppu2 to use the default registers by sending him 5 volts on pins 45 and 46.
This chip has many uses inside games.
Last edited by dlfrsilver; 03 January 2013 at 19:57.