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Maybe they forgot about them? I mean the VA6.8 *still* has them and the markings of 5402:VA5 | 5433: VA6, except it says V6.8 on IC BD M5.. text

My Japanese MD1 says "IC BD M5" on the board, no VAxx.

The VAxx is near the I/O + bus arbiter chip.

Here's a picture of someone else's VA5:

http ...

Jorge Nuno wrote:I challenge you to remove them on a USA/EU VA6 (the EOE/NOE wires)

That's interesting. But why keep the wires anyway ?

MD1 VA5 and VA6 have the exact same PCB.

What make a VA5 (exactly as it's written on the PCB) is the I/O + bus arbiter chip be 315-5402. The slightly different copper you mention is a Asian model which has built in RF modulator. That makes it look very close to the "EXPORT" (aka European/USA ...

I made these pictures from my VA6 Japanese MD1:

https://lh6.googleusercontent.com/-91PKWr6aUlY/VQR7x7_G2UI/AAAAAAAAIVo/4clIYPkcW9Q/s800/DSC02473.JPG
The green wire links VDP pin 119 (/RAS0) to the /CS pin on both of the PSRAM chips working as the CPU work ram.

Yellow and blue on the other side ...

I know this post is old... But you deserve a reply.

The 220 ohm resistor on /AS at the 68000 is put when the console is using a FC1001 VDP (315-5313A) with a Motorola CPU. When the CPU is Hitachi CMOS HD68HC000, like this one:
http://www.retroisle.com/others/segamegadrive/Pictures/images_technical ...

Apparently KRIKzz is unaware of the HINT stuff (register $A12006 and vector $000070) thus Mega Drive everdrives glitch a lot on CD stuff:

http://krikzz.com/forum/index.php?topic=1936.0

This is the simplest I could get with the parts I have here:
https://lh6.googleusercontent.com/-EmabhILEvbo/VLNC74PrZhI/AAAAAAAAIEw/2m3esuARsfs/s800/mega-cd_bios_from_cartridge.jpg

Tomorrow I'll assemble that and debug/change if there's any mistakes with address decoding.

For now I found out a ...

https://lh4.googleusercontent.com/-JR-L-0MKPlw/VLLBBe1IFZI/AAAAAAAAIDw/AX-Yrdu4rsM/s800/mega-cd_bios_from_cartridge.jpg
(wip)


I am still working on the logic which toggles /CART HIGH when the HINT vector is read so the MCE chip has control of HINT address. (that's what the 7430s being drawn will ...

TmEE co.(TM) wrote:Now I see how it would work, I had a brainfart.

You will have to deal with TMSS first though, otherwise it gets in the way.

Not really, my Mega Drive is a VA3. And I'm going to only test patches and the translation of the Japanese BIOS to English I wanted to do since forever ... lol

TmEE co.(TM) wrote:I'm not seeing how that would work... BIOS in CD side is always visible...

/CART high makes it go to $400000... No conflicts.

Tomorrow I'll try to implement it with just a 74LS138... If it works like I think it does, there won't even be issues with mirroring or anything similar.

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.

That gave me a idea for testing modded CD BIOSES without opening the ...

An computer built around 68000 CPU would have a counter and logic circuit to trigger an BUS ERROR exception using the /BERR (Bus Error) pin on the CPU after a set number of machine cycles without /DTACK pulse. MD doesn't have that because was built with cost saving in mind.

I don't think anyone will have any trouble with SEGA from reusing/copying their BIOS.

Also, documenting everything at a centralized place is a great idea.


Really, at this point in time I can't see them complain about anything but the copying of the games. And even that is highly unlikely to ...

A few hours more of work poured on this:

Euro ROMs do consistently use the same security data as the CD. You can make a single cart which will boot on any un-modded PAL system out there.

That's a good thing.

For USA consoles things are a little grim:

The tray model SEGA-CD with BIOS 1.10 use ...

For debugging purposes I'd like to suggest:

This boot method:
http://gendev.spritesmind.net/forum/viewtopic.php?p=14320#14320

Coupled with some RAM on cart and some hardware for uploading cross development builds being tested.

The cart could be something like this:

0x400000-0x40FFFF SEGA ...