Mapper 23 reproduction question

jpx72 · Post by **jpx72** » Sun Oct 17, 2010 10:15 pm

I've recently purchased Ganbare Goemon Gaiden - Kieta Ougon Kiseru cartridge (still on the way) and I am wondering if it could be changed to Contra (J).
I've found that GGGaiden is mapper 22 (VRC2 Type A) and Contra(J) is Mapper 23 (VRC2 type B). I wasn't able to find any info about pinouts of these Konami Roms (when I get the cartridge, I will try to trace them myself), but I am concerned about the different mapper.
Is it really so different? Will GGGaiden cartridge work with the Contra (J) rom? Thanks.

Banshaku · Post by **Banshaku** » Sun Oct 17, 2010 11:59 pm

I will just use an educated guess. Since emulator required 2 different mappers to make them work, the chance are high that it will not. The only way to know is to check what are the mapper difference inside the code of a current emulator. If, for examples, registers are different (like Castlevania 3 and Madara) then unless you hack the rom then it would not be possible to use "as-is".

jpx72 · Post by **jpx72** » Mon Oct 18, 2010 12:11 am

Thank you, I expected this conclusion. I'm wondering if there's some detailed information about these mappers somewhere? Could't find any here on nesdev wiki...

thefox · Post by **thefox** » Mon Oct 18, 2010 12:24 am

http://www.romhacking.net/docs/362/

E: seems all the same info is also on wiki... http://wiki.nesdev.com/w/index.php/VRC2

jpx72 · Post by **jpx72** » Mon Oct 18, 2010 3:37 am

Ahh thanks, didn't hit me to search for the VRC2.

MottZilla · Post by **MottZilla** » Mon Oct 18, 2010 9:03 am

Contra (J) has been hacked to mapper 4 (MMC3) by Bregalad which is far more common. http://jonathan.microclub.ch/contra/

jpx72 · Post by **jpx72** » Mon Oct 18, 2010 10:15 pm

Yes, thank you, I have been able to reproduce this hacked version by using the SMB3 cartridge. But I would rather have the original rom up and running on a cartridge with the VRC2 chip.

MottZilla · Post by **MottZilla** » Tue Oct 19, 2010 8:31 am

VRC2A and 2B differences:

You will need to swap A0 and A1.

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   variant   lines     registers                       Mapper Number
   =================================================================
   VRC2a:    A1, A0    $x000, $x002, $x001, $x003      022
   VRC2b:    A0, A1    $x000, $x001, $x002, $x003      023

Also this may or may not be an issue with your particular game.

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Important note!  On VRC2a (mapper 022) only the high 7 bits of the CHR regs are used -- the low bit is
ignored.  Therefore, you effectively have to right-shift the CHR page by 1 to get the actual page number.

jpx72 · Post by **jpx72** » Tue Oct 19, 2010 11:19 am

Thanks for pointing out the important parts, when I get the cartridge, hopefully I would be able to make something out of it...well swapping the two adress lines shouldn't be a problem, but I don't know anything about romhacking so shifting the CHR page is out of my league, hopefully this won't be needed...

jpx72 · Post by **jpx72** » Sat Oct 30, 2010 1:08 pm

I finally received the Ganbare Goemon Gaiden - Kieta Ougon Kiseru cartridge. Can somebody please help me with the pinout? This is what I've found out so far (PRG=pin on PRG ROM, VRC = pin on VRCII chip and CNN is the cartridge connector):

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scratched project

[/code]

kyuusaku · Post by **kyuusaku** » Sat Oct 30, 2010 10:13 pm

If you want the game and want the original mapper (what difference does it make?? You can remove the crappy translation...), why don't you just buy the original cart?! It's not even that expensive. Goemon Gaiden is a good game you're sacrificing :(

jpx72 · Post by **jpx72** » Sun Oct 31, 2010 3:09 am

I haven't found Contra cartridge for less than cca 30USD (shipping incl.). GGG cost me 3€ and I have eproms for free. It's a big difference for me. I can send the original roms to anybody for the postage cost if that means something. But I like to keep those if I ever want to revert the conversion process.

MottZilla · Post by **MottZilla** » Sun Oct 31, 2010 9:06 am

I still don't understand why you aren't happy with the MMC3 version. There is no real difference. It's the same game. I agree with kyuusaku. It's a waste what you are planning to do or are doing. I don't understand what there is to gain.

jpx72 · Post by **jpx72** » Sun Oct 31, 2010 12:31 pm

Hmm well from what I've read, the MMC3 version isn't 100% flawless, and you cannot aply contra ips patches to it. And to prove myself that I can do it is also important. The whole process is fascinating.

MottZilla · Post by **MottZilla** » Sun Oct 31, 2010 5:31 pm

Fascinating? You swap out the ROM chips for something else. Not really that amazing. What do you mean apply contra IPS patches to it? Not that it's the end of the world that you destroy this game to make a bootleg, but the problem is there are lots of people that are all thinking the same thing. Pretty soon, the game will be extremely rare to come by.