SpritesMind.Net

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) models...

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 are t...

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/M...

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 few g...

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 do...

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 Mega C...

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 happen.

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 the sam...

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 security co...