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How do modern NES games get around the CIC chip? (lemmy.ml)

submitted 2 years ago by atocci@lemmy.ml to c/gaming@lemmy.ml

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I had the chance to pick up a copy of 8 Bit Music Power Final recently, a NES game released in 2021! Before this, I hadn't even realized games were still being developed for the NES, let alone receiving commercial releases.

I'm sure Nintendo has nothing to do with this continued support though, so it got me wondering about the CIC lockout chip. Supposedly, it should be in every officially licensed cartridge for the NES, and without it the console will refuse to start and repeatedly reset. Without Nintendo licensing games anymore though, how are these new releases managing to get around this?

I know there were unlicensed cartridges that used a brute-force method to bypass the chip back then, but these new games don't seem to be doing the same thing as those. Was the lockout chip reverse engineered at some point and that's how it's done now? I can't find too much information on this, but I'd really like to know how it works.

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[–] Garrathian@beehaw.org 13 points 2 years ago (1 children)

https://www.youtube.com/watch?v=x8PYE8A-WEw

This guy has a pretty good video that discusses it. The short answer is that Atari in the 80s had filed a case in court and got the NES CIC chip code, and made an equivalent Rabbit CIC chip for their bootleg games (he goes more in detail about all of that). Later on the homebrew community struggled to reverse engineer the NES CIC chip or get it to dump it's CPU instructions. However they found out Atari's Rabbit one would dump the CPU instructions that were equivalent to the ones NES CIC used. So they used those instructions to reverse engineer the chip, which allowed homebrew games to be developed for the NES with the reverse engineered homebrew chip

[–] atocci@lemmy.ml 3 points 2 years ago

Wow thank you, that's super interesting and exactly what I was looking for! Amazing that it took more than 20 years for it to be figured out.

[–] taylus@lemmy.ml 3 points 2 years ago

I love the homebrew scene for these old consoles. I don’t know exactly what modern carts are using but this gives more general info: https://www.nesdev.org/wiki/CIC_lockout_chip#Defeating