MegaCD2 Japan Bios on PAL MegaCD2
Moderator: Mask of Destiny
MegaCD2 Japan Bios on PAL MegaCD2
I have an Everdrive, and a Megadrive 2 + MegaCD 2, both PAL.
I found that I can boot the Japanese MegaCD 2 Bios using the everdrive, so I bought some Japanese games and some are running very well (time gal, ax-101)
Unfortunately, some other games aren't
For example, microcosm and starwars won't boot -> black screen, or starblade will start, show title screen, then hang when starting a new game.
I tried to mod my megadrive with a 50/60hz switch, but even in 60hz mode, it won't fix the problem.
Do I need to add the usa/japan switch ? or any other modification ?
I found that I can boot the Japanese MegaCD 2 Bios using the everdrive, so I bought some Japanese games and some are running very well (time gal, ax-101)
Unfortunately, some other games aren't
For example, microcosm and starwars won't boot -> black screen, or starblade will start, show title screen, then hang when starting a new game.
I tried to mod my megadrive with a 50/60hz switch, but even in 60hz mode, it won't fix the problem.
Do I need to add the usa/japan switch ? or any other modification ?
Retro game programming !
I switched my Megadrive with both 50/60Hz + USA/Jap switch.
I start the Megacd 2 Japanese Bios from the Everdrive in 60Hz/JAP mode.
And the 3 games that weren't working before (in 50Hz/PAL) still don't work in 60Hz/JAP :/
So, I guess, this might be an everdrive incompatibility.
Jap Games not working: Starwars rebel assault, Microcosm, Starbalde
Jap Games working (in any mode): Time Gal, AX-101
I start the Megacd 2 Japanese Bios from the Everdrive in 60Hz/JAP mode.
And the 3 games that weren't working before (in 50Hz/PAL) still don't work in 60Hz/JAP :/
So, I guess, this might be an everdrive incompatibility.
Jap Games not working: Starwars rebel assault, Microcosm, Starbalde
Jap Games working (in any mode): Time Gal, AX-101
Retro game programming !
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I have to admit i never tested these games but i don't see how can it be an everdrive incompatibility. The Everdrive basically maps the loaded BIOS to the usual MegaCD BIOS area so at this point it should be 100% compatible.
If the issue is region, you should have a message anyway...
I would say that at soon you Megadrive is correctly clocked (60 Hz) then it should work. The MegaCD clock stay the same whatever is the region.
If the issue is region, you should have a message anyway...
I would say that at soon you Megadrive is correctly clocked (60 Hz) then it should work. The MegaCD clock stay the same whatever is the region.
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How does the Everdrive work for this case exactly? I'm not aware of any mechanism that would allow the rest of the CD hardware to be mapped appropriately, but leave the BIOS area unmapped and it's not like it sits between the original BIOS ROM and the 68K so it can't intercept the read. Is it just driving the bus harder than the ROM on the board?
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I don't see any other mechanism possible besides making a bus fight and winning it.
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Maybe by watching address bus and toggling CART_IN during BIOS access?Mask of Destiny wrote:How does the Everdrive work for this case exactly?
toooo many zeroesss 0x40000000raq wrote:Isn't it the case when a cart is inserted the CD BIOS (the original one in the Mega-CD) gets mapped to 0x40000000 and cart is mapped to 0x00000000 and this swaps around when cart is removed?
And with that you get CD's RAMs and stuff mapped at 400000+ too, which is not what the BIOS expects.
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That gave me a idea for testing modded CD BIOSES without opening the Mega CD !raq wrote: There is a bit in the config register of the everdrive thats set when a BIOS is flashed to the everdrive, so maybe the fpga traps addresses 0x20000 - 0x3ffff and 0x200000 - 0x23ffff and sets CART_IN high when in this range.
I was curious about how this worked and I even asked Tiido about this. He said he thought it fought the BUS using the 68000 bus control lines. But using /CART makes a lot more sense in the end.
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I'm not seeing how that would work... BIOS in CD side is always visible...
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