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Someone asked about Pro Action Replay code support in the Neo Myth, so I looked around. You know, there's virtually nothing about the PAR for MegaDrive anymore. Other than a very brief description, I couldn't find anything about it.

Does anyone know how the PAR codes are derived? Game Genie is pretty easy - everyone supports that - but PAR would be nice too.

PAR code is aaaaaa:dddd

Where "a" is 24bit 68K address and "d" being data. PAR works for ROM and RAM so lot of fun can be done with it

Yep, that was me who asked.

Yeah, there's little to no information out there about the PAR. There's even less information for Game Gear/Master System PAR, sadly.

I know Steve Snake would know this stuff since he's done it for Kega. Next time I speak to him I'll ask him about the full technical details on the PAR (and maybe for the GG/SMS too). I know Eke has (semi?) working on PAR ROM support in Genesis Plus GX. This stuff really needs to be documented since the PAR is actually very useful and very important.

But yeah, it's actually superior to the Game Genie since it can do both ROM and RAM as Tiido said (you can use hex decrypted Game Genie codes in a PAR).

P.S. You have any idea how rare the PAR carts are?!? I just spent over $40 for one that works on the Mega Drive - fortunately PAR carts aren't region locked so it'll work fine on a US Genesis!

I know Eke has (semi?) working on PAR ROM support in Genesis Plus GX. This stuff really needs to be documented since the PAR is actually very useful and very important.

actually, this was more for the fun of supporting these ROMs properly, this is completely unecessary if you just want to add support for PAR codes. As said above, the code format is even simpler than the Game Genie one, it's a simple memory address followed by a data patch value, there is nothing more you need to handle PAR codes...

For the record, Pro Action Replay (1 & 2) cartridges have on-board RAM (64KB I believe), which is used as scratch RAM by the internal ROM program and its "trainer" module. It's mapped at $420000-$42ffff on Pro Action Replay, $600000-60ffff on Pro Action Replay 2. There are also some internal registers mapped in lower memory space. The PAR 1 stores cheat codes (max. 4) in those registers whereas PAR2 store them in its on-board RAM (that's why they advertised that an "unlimited" amount of codes could be used).

The Action Replay (not Pro) cartridges does not have any extra RAM, only some registers which hold codes (address + data) in a strange interlaced way that I figured out by analysing the ROM program while inputting codes. The Game Genie hardware is actually doing something similar, it has been documentedsome time ago.

Regarding the Neo Myth, it doesn't really matter how original carts where working, it would just have to patch the ROM data for codes that access ROM area, and have additional hardware to catch RAM read/writes (easier to say than doing it though), decoding PAR codes is actually the easiest thing in the process.

P.S. You have any idea how rare the PAR carts are?!? I just spent over $40 for one that works on the Mega Drive - fortunately PAR carts aren't region locked so it'll work fine on a US Genesis!

wow, that's expensive. Surprisingly, I still have the PAR I bought 15 years ago , and accidentally got a german PAR 2 cart in a game lot, unfortunately the switch is broken and stuck to off position which makes it unusable

Heh, I wish someone would do a technical document on the PAR hardware itself like Charles did for the Game Genie but like you said, it's easy enough to support. For the Game Gear at least, I believe it uses the $0000-$BFFF ROM area if I'm not mistaken. Not sure about the Master System though.

Yeah, I bought a PAR1 but if I see a PAR2 advertised on eBay or wherever, I'll pick it up.

Alternately you could patch a ROM with the Classic Cheat Code Game Patcher before burning it to the flash cart and it *should* work fine - but personally I wouldn't do this.

King Of Chaos wrote:but if I see a PAR2 advertised on eBay or wherever, I'll pick it up.

This must be my lucky thread because I found a few and finally ordered one. I also found a model 1 Sega CD which I was looking for too!