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mapper 66?
http://forums.nesdev.com/viewtopic.php?f=3&t=15263
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Author:  Zepper [ Sun Dec 18, 2016 4:04 pm ]
Post subject:  mapper 66?

I'm doing a revision in my emulator mappers. Let me start by 66. In my notes, bit $80 of the value wriiten would control the PPU mirroring... but I suppose it's incorrect, right? Plus, is possible to use mapper 66 with CHR RAM?

Author:  Myask [ Sun Dec 18, 2016 4:16 pm ]
Post subject:  Re: mapper 66?

Looks wrong to me. No "mapper-controlled" mirrorings anywhere in there, nor on the wiki.

Took a bit to find where it was, but it's supported by FCEU source.

edit: Nintendulator likewise has no mirror register. Does appear to support CHR_RAM (allows only two address lines in code)

e2: Nestopia also says no mirroring register.

Author:  tepples [ Sun Dec 18, 2016 4:18 pm ]
Post subject:  Re: mapper 66?

GNROM uses fixed mirroring. Bit 7 does not change the mirroring type. To set the board to vertical mirroring, bridge the H pad on hardware or set bit 0 of byte $0006 in an iNES ROM.

And yes, almost any mapper that can use CHR ROM can also use CHR RAM. (Those that don't would have to intercept the PPU bus data lines. But even MMC5 doesn't appear to truly intercept these lines; it just acts as an additional memory.) To tell the emulator that you've modified the board to accept a 62256 or compatible SRAM, you'll need to make an NES 2.0 header specifying 32K as the RAM size.

Author:  Zepper [ Sun Dec 18, 2016 5:06 pm ]
Post subject:  Re: mapper 66?

OKay, thanks so much.

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