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PostPosted: Thu Jan 03, 2019 5:32 pm 
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With CPU A0,1,12,13,14, and ROMSEL, (i.e. 6 address bits) it gives rise to 64 possible registers in VRC6:
Code:
 $0000, $0001, $0002, $0003, $1000, $1001, $1002, $1003,
 $2000, $2001, $2002, $2003, $3000, $3001, $3002, $3003,
 $4000, $4001, $4002, $4003, $5000, $5001, $5002, $5003,
 $6000, $6001, $6002, $6003, $7000, $7001, $7002, $7003,
 
 $8000, $8001, $8002, $8003, $9000, $9001, $9002, $9003,
 $A000, $A001, $A002, $A003, $B000, $B001, $B002, $B003,
 $C000, $C001, $C002, $C003, $D000, $D001, $D002, $D003,
 $E000, $E001, $E002, $E003, $F000, $F001, $F002, $F003

It seems that all registers are located in the range $8000-FFFF. We have documentation in the wiki for every register in this range except for $A003. Does anyone know anything about it? I only have 1 VRC6 at the moment, which I care not to take apart, but could get another to play with if this should be investigated.


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PostPosted: Thu Jan 03, 2019 5:50 pm 
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We have the official leaked documentation about the VRC6, which NewRisingSun transcribed and translated here viewtopic.php?t=17137

If there's something there, it's not something Konami documented in-house.


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PostPosted: Thu Jan 03, 2019 6:02 pm 
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lidnariq wrote:
We have the official leaked documentation about the VRC6, which NewRisingSun transcribed and translated here viewtopic.php?t=17137

If there's something there, it's not something Konami documented in-house.

Okay, thanks for the info.


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PostPosted: Thu Jan 03, 2019 11:41 pm 
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I believe I tried writing various values to it while audio was active to try to determine if it had audio function. This was how $9003's function was determined. I didn't find any audio function from these tests, though I don't have a rigorous record of what was tried.

BTW Hotswap tests can be used to investigate the mapper if you don't want to take the cartridge apart. You don't quite have direct access that way, but there's still a lot you can do.


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PostPosted: Fri Jan 04, 2019 11:34 am 
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rainwarrior wrote:
I believe I tried writing various values to it while audio was active to try to determine if it had audio function. This was how $9003's function was determined. I didn't find any audio function from these tests, though I don't have a rigorous record of what was tried.

BTW Hotswap tests can be used to investigate the mapper if you don't want to take the cartridge apart. You don't quite have direct access that way, but there's still a lot you can do.

Thanks rainwarrior, I should make an adapter that goes from edge connector to my setup for this purpose. My VRC6 is a Madara cart that I modified with lots of plastic insulated wires inside, turning it into a flashable multicart for Castlevania III, Madara(English), and also the ability to select the original Madara (J) ROMs. Unfortunately, it watches toggles to CPU A0 and if it sees too big of a gap, attempts to swap ROM chip selects and regions to a different game, so there are some extra variables to worry about... I did leave the ROM chips accessible from outside the cart, so I could write a 6502 program and flash it on there... There are definitely options here.


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