MegaCD/SegaCD import mods?

[Guest_Aidan]

I've been looking for details on import mods for the Mega CD/Sega CD (I'm from the UK, ok?), and I've been falling short on details, despite a good few googles.

As I've found so little details, I'm going to ask questions here. If there's no easy way to do it in hardware, is the lockout controlled by the BIOS in the CD unit? If so, I might see if I can get hold of alternative BIOSes, and blow the three of them into a single EPROM/FLASH, and add a selector to choose which BIOS it should be using.

Of course, I'll have to get hold of a megaCD unit that can be sacrificed first!

[Sonic Freak]

You've probably already seen it but http://arakon.dyndns.org/tutorial/bios.html has some details about adding a multibios eprom to a Mega CD/Sega CD.

[Guest_Segasonicfan]

that mod looks VERY hard...has anybody successfully completed it?  And woudl that work with a CDX?  If so, I'm gonna go off and try it myself....

Also, it doesn't say you need another bios chip or anything, is he just talkin about te one built into the system?

-Segasonicfan

[Aidan]

Thanks for the link - I knew I'd seen it ages ago, but couldn't find it anywhere!

You would need a new BIOS chip that has four times the capacity of the original one. The way it works is it allows you to switch which BIOS the mega cd unit 'sees'. That way you can set it to a US BIOS, or a European BIOS, or a Japanese BIOS.

It's probably possible to add some code to remove the country coding all together, but I understand that the Japanese BIOS has some extra code that the others don't. That would make things more difficult, and I've not really looked into that aspect.

[Sonic Freak]

It's probably possible to add some code to remove the country coding all together

On the website near the bottom in the thanks section is says:

Ex-Cyber for removing the country check in the BIOS

Also http://www.eidolons-inn.net/tiki-index.php?page=Projects has the multibios installation, along with loads of other good stuff

P.S If anyone does know where a bios with the country check removed, let me know where I can get hold of it please

[Arakon]

unfortunately so far it has NOT been possible to make a single bios which is region free.. might not be possible at all without a complete rewrite because of the way the segacd's country protection works. the region checked mentioned on my page is for the genesis region check, so you don't get a "this system is only for use in xxx" message every time unless you switch your genesis too.

[Aidan]

As far as I understood it, the SegaCD's BIOS checked the boot sector of the CD against a stored 'known good' version. Now, I've not done any disassembly, so I've not looked at the code myself yet!