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Arakon...about your mega cd bios chips

Discussion in 'Genesis/Mega Drive' started by jimmy_s, Apr 29, 2002.

  1. jimmy_s

    jimmy_s New Member


    How do I buy one of your Mega CD multi bios chips?

    How much do they cost?

    I've read your installation guide, so do the switches just change between PAL/NTSC and between the JAP/USA/PAL bios data?

  2. Arakon

    Arakon New Member

    the switches have 4 possible combinations (up-up, up-down, down-up, down-down). 3 of those are a different country's bios (US, jpn, euro) and the 4th combination enables the game Columns.
  3. maidtina

    maidtina New Member

    Arakon, how the hell did you manage to get it to take a megadrive game in the bios chip? any way you could add a different game? or using a bigger rom get it to play many different games? just interested in persuing this technology
  4. flavio75

    flavio75 New Member

    Arakon, does your multi-bios also work with the Genesis CDX system ?


    Flavio [​IMG]
  5. ExCyber

    ExCyber Staff Member

    It's quite simple; the "expansion port" is almost identical to the cartridge slot, as far as the presence and behavior of main signals go (the main cart slot has a bunch of stuff that almost never gets used). When the MD runs the BIOS, it pretty much sees the ROM as it would any cart ROM. Put a game there instead of a BIOS program, and it runs the game.

    It can be done, but it was Columns for a reason - putting three BIOS images on a single ROM leaves a fourth of the ROM unused. Since it's a 4Mb ROM, that leaves a big 1Mb for the game. There aren't many 1Mb MD games (fewer than ten I think, and presumably most of them aren't that great). Using a bigger ROM would require soldering additional connections, and would waste more of the ROM. An SMS game can't be done because the M3/SMS mode pin isn't available at the expansion slot, and you'd be limited in your selection there too because SMS games bigger than 48KB require a mapper chip.
  6. Arakon

    Arakon New Member

    the CDX unfortunately uses a surface mounted bios rom, which means you'd need to desolder that and wire up the socket to those pins. considering the VERY little space inside the cdx, I don't think that'd be possible.
  7. kyosuke75

    kyosuke75 New Member


    Are you planning on selling the bios chip? I think that's a really cool idea...

    Does it work on a Jvc x'eye?

  8. Arakon

    Arakon New Member

    heh.. I've been selling them for a while, on and off whenever I got enough orders to make ordering blanks worth it.

    the x'eye suffers from the same problem as the CDX.. surface mounted bios with different pinout. there's more space, and should be possible, but will be lots of work.
  9. maidtina

    maidtina New Member

    hey arakon, any chance when i order this thing i can get another rom burned with some games on it? the rare ones are so hard to find now. People just either sell their consoles with all their games or bin the carts now. All second hand shops no longer take in megadrive games. Will etch myself a board with all the roms on and wire a big ass rotary switch to control it
  10. Arakon

    Arakon New Member

    "some games on it"?

    the largest eprom I could burn is 8 mbit = 1 MB.

    there are no normally available 40 pin, 16 bit eproms larger than that.
  11. Arakon

    Arakon New Member

    and mind you, for the price of an 8 mbit eprom you can buy several games.

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