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 Post subject: VRC6 Address change
PostPosted: Sun Feb 06, 2005 11:07 pm 
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I got VRC6 (iNES mapper #24) working for Akumajou Densetsu. Now I'm under the impression that the "other" VRC6 (iNES mapper #26) operates the exact same way... only the addresses are flipped around.

I've been switching $xxx1 and $xxx2 addresses around for mapper #26. I'm trying to get Madara running -- the title screen comes in fine, but when you select a save file is crashes (hits a bad opcode -- PRG swapping problem?)

I have the $8000 reg select the 16k PRG page at $8000, and I have $C000 select the 8k PRG page at $C000. This works for Akumajou Densetsu... but apparently not for Madara (I haven't tried Esper Dream 2 yet).

Are there other PRG swapping registers? Am I right in flipping the xxx1 and xxx2 addresses around? I couldn't find any info that addresses this subject on the site or on the old boards. Any help appreciated ^^


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PostPosted: Mon Feb 07, 2005 7:57 am 
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Formerly Fx3
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The differences I've found are:

Code:
IRQ registers (operation):
map24: F000,F001,F002
map26: F000,F002,F001

Mirroring (value & 7Fh):
map24: 0x08 and 0x28 are the same.
map26: 0x08 and 0x2C are the same.


Other than that, it's the same.

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 Post subject:
PostPosted: Mon Feb 07, 2005 11:05 am 
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Fx3 wrote:
The differences I've found are:

Code:
IRQ registers (operation):
map24: F000,F001,F002
map26: F000,F002,F001

Mirroring (value & 7Fh):
map24: 0x08 and 0x28 are the same.
map26: 0x08 and 0x2C are the same.


Other than that, it's the same.


Not quite... the CHR bankswitching registers ($D000-$D003, $E000-$E003) are also 'rearranged' (as D000/D002/D001/D003 and E000/E002/E001/E003). Mirroring only uses $B003 bits 2-3, so 0x08/0x28 would be identical (though 0x08/0x2C would be two different 1-screen mirroring modes).

The exact difference is that A0 and A1 are connected 'normally' on mapper 24 and are connected 'backwards' on mapper 26 - other than that, they are the exact same chip.

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 Post subject:
PostPosted: Mon Feb 07, 2005 5:47 pm 
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Formerly Fx3
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So, is the mirroring exactly the same on both mappers? I mean, 08h & 28h are the same setting.

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PostPosted: Mon Feb 07, 2005 6:52 pm 
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Haw... apparently my troubles were because I forgot to put RAM at $6000-$7FFF XD. I guess Akumajou Densetsu doesn't use it so that's why I didn't catch it earlier.

Everything seems to be working now ^^


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