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Mapper 255
http://forums.nesdev.com/viewtopic.php?f=3&t=12647
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Author:  lidnariq [ Thu Dec 14, 2017 4:22 pm ]
Post subject:  Re: Mapper 255

... wait, isn't that exactly mapper 225?

Author:  GreyRogue [ Thu Dec 14, 2017 4:34 pm ]
Post subject:  Re: Mapper 255

nesrocks wrote:
I'm not sure if it's still not properly dumped or an emulator bug, but I'm super interested in this and I had no idea he had dumped it. I promptly went to test it on emulators and the page changing on the games list bugs on the last page and the second to last page. Try moving the cursor from below and from above. Different bugs but neither works. Also, can't start games from #105-#110. Using nestopia 1.40.

As mentioned in this thread. There is a RAM chip missing from the board. Nestopia does not add this to its emulation. This makes it more accurate to the actual (known) cart. Adding support for the RAM chip depends on whether you want it to work as intended or as implemented, at least until a cart with the RAM populated is found. I'm not sure if that's an intentional choice for Nestopia or not or if they recognized it was designed to have a missing 74670. If you want wrapping to work, you'll need to build your own. The hacks/cheats used in the high numbered games will also not work as expected, as the value used there is also written to the missing RAM chip. The code I posted works with FCEUX (I just threw it into the existing Supervision cpp file for convenience), and just needs the 255 Mapper uncommented: the first one without RAM support; the second with. Adding it to Nestopia would be pretty straightforward.

Author:  nesrocks [ Thu Dec 14, 2017 4:45 pm ]
Post subject:  Re: Mapper 255

I'm sorry if this is unwanted or poluting, but I have the 72 pin version of this and I took some photos. Maybe they are interesting somewhat. (nevermind my gradius and arkanoid tips stickers)

Image
Image
Image
Image

Author:  GreyRogue [ Thu Dec 14, 2017 4:58 pm ]
Post subject:  Re: Mapper 255

lidnariq wrote:
... wait, isn't that exactly mapper 225?

Ha. Sure looks like it. I note that Nestopia keeps them separate and doesn't implement the shared high bit on 225 for some reason.

nesrocks wrote:
I'm sorry if this is unwanted or poluting, but I have the 72 pin version of this and I took some photos. Maybe they are interesting somewhat. (nevermind my gradius and arkanoid tips stickers)

Image
Image
Image
Image

And there's a version with the missing 74670. Nice.

Author:  nesrocks [ Thu Dec 14, 2017 5:19 pm ]
Post subject:  Re: Mapper 255

So, were you just looking for the information on the chip or do you want me to do something about it? XD I think I know a friend who could dump it but maybe he can't and haven't talked to him in a while.

Author:  GreyRogue [ Thu Dec 14, 2017 6:09 pm ]
Post subject:  Re: Mapper 255

nesrocks wrote:
So, were you just looking for the information on the chip or do you want me to do something about it? XD I think I know a friend who could dump it but maybe he can't and haven't talked to him in a while.

Whether you dump or not is up to you. I assume you'll get same thing I did and that CaH4e3 did in 2011. Our PAL contents would be different, as yours only has 3 ROM chips instead of the 6 mine has, but I assume yours are 1MB instead of the 512KB in mine. I think this also explains why I wasn't measuring anything from the PAL to my unpopulated socket. They had redone it when they changed to 512K chips. I apparently only got a pirate copy of the pirate cart (Pirateception), which is why mine is missing the 74670. I should demand a refund! I demand only the finest original pirate carts when purchasing famicom adapters.

Author:  nesrocks [ Fri Dec 15, 2017 6:11 am ]
Post subject:  Re: Mapper 255

Okay... So let me see if I got this right:

- due to the lack of extra ram chip the cartridge you got has the same behavior as the emulated version (bugged last page).
- meaning the emulation is correct for your cartridge.
- meaning it's possible to correctly emulate the version I have (that fully works because the ram chip is present) and you've done it with the code you posted for the ram version.
- the code you posted is meant to be used on fceux source.

All correct?

Author:  krzysiobal [ Fri Dec 15, 2017 7:29 am ]
Post subject:  Re: Mapper 255

Quote:
Our PAL contents would be different

Rather not, they're probably the same. PAL is not responsible for decoding ROM - it is 74*139's role. THe cartridge latches 15 address bits.
In the NES version there is 74*174 (=6) + 74*273(=8). Probably one of 74*74's gates latches the fiftenth bit and second gate is used as inverter to select between one and the other PRG rom.

Please dump PAL content to confirm the combinatory logic I suggested in my schematics. Be advised, that some of I/O pins are used as inputs. .

Author:  lidnariq [ Fri Dec 15, 2017 10:44 am ]
Post subject:  Re: Mapper 255

krzysiobal wrote:
PAL is not responsible for decoding RAM
Yes it is? By RAM we mean the 74'670.

Author:  krzysiobal [ Fri Dec 15, 2017 11:04 am ]
Post subject:  Re: Mapper 255

Sorry, I mean ROM.

Author:  zxbdragon [ Mon Jan 08, 2018 2:51 am ]
Post subject:  Re: Mapper 255

this cart, I dumped,mapper 255.

mapper 255,have 10 or more cart!

Attachments:
ines52_001.png
ines52_001.png [ 3.84 KiB | Viewed 1368 times ]

Author:  krzysiobal [ Tue Jan 09, 2018 4:46 pm ]
Post subject:  Re: Mapper 255

Congratulations, but how can we help you? When do China holidays start?

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