Files over 4MB

[Ice Man]

Hello there,
I was trying to make a 8MB or even 12MB cartridge.
However, how exactly would one do this with 3x27c322 + 74LS139?
I heard that $A00000-$BFFFFF are built in and can't be accessed. Is that correct?

I have found a schema that allows me to use 2x27c322 but will it work for 3 as well? (Mainly UMK Trilogy)



Credits to oofwill

Here's another schema but this won't work.

http://imgur.com/ERBbHB4

[Charles MacDonald]

Hello there,
I was trying to make a 8MB or even 12MB cartridge.
However, how exactly would one do this with 3x27c322 + 74LS139?
I heard that $A00000-$BFFFFF are built in and can't be accessed. Is that correct?

There's some issues when making cartridges larger than 4MB:

1.) 400000-7FFFFF is used by the Sega CD, so if the Sega CD is plugged in there will be a conflict between it and the cartridge. Otherwise it is safe to use.
2.) 800000-9FFFFF is used by the 32X. It may be safe to use this region if the 32X adapter enable bit is turned off though. If you use it, you will need to assert DTACK when this range is accessed.
3.) The B00000-BFFFFF area is free for use. You will need to assert DTACK when this range is accessed too. You are correct that A00000-AFFFFF can't be used.

Using any of these areas only works for homebrew software. Commercial games larger than 4MB use a banking scheme instead, instead of mapping their ROM to higher addresses.

[Ice Man]

I've seen people using an Everdrive to run Ulitmate Mortal Kombat Trilogy for example. How exactly would this work since the game is 10MB or more by now.

Is there a way I can still access $A00000-$AFFFFF?

Would connecting a 3rd EPROM work as well by just adding the /OE signal to the 10th pin of the 74LS139 shown in the schematic?

[Eke]

I've seen people using an Everdrive to run Ulitmate Mortal Kombat Trilogy for example. How exactly would this work since the game is 10MB or more by now.

Mega Everdrive generates its own /DTACK signal on the B20 pin when accessing the $800000-$9FFFFF area
Maximal supported size is 10MB, the 12MB ROM hack won't work.

Is there a way I can still access $A00000-$AFFFFF?

No because it will result in access conflict with Z80 area (which includes the FM chip) and I/O area. There is some room in the upper area that is not used by anything but it is advised that you do not put any usable data here in EPROM.
The 12MB UMK3 hack you are talking about has nothing there for example, and the program never tries to read from ROM at these addresses, it's simply wasted space in ROM.

Would connecting a 3rd EPROM work as well by just adding the /OE signal to the 10th pin of the 74LS139 shown in the schematic?

No, it won't work because you need a specific /CE for the third EPROM, the one in this schematic which uses either /ASEL (B26) or VA23 (B11) only covers $000000-$7FFFFF area.
Also, pin 10 of the 74LS139 triggers the whole $800000-$BFFFFF area, you would need two additional address lines and different decoding logic to skip the $A00000-$AFFFFF area.

[Ice Man]

Oh, I see. Thanks for the information.
Going to try this later.

[r57shell]

It's our scheme!!!

r57shell & Nemesis_c

Image link - to our site. And Russian comments.
And credit to "oofwill"? Who is that? I didn't heard about him before.

I hate those, who steals info, and make credits.

[Ice Man]

I gave credit to him because he posted it here. I don't know about original author. Misleading information I'd say. Sorry for that.

Either way, thanks for the real link to homepage.

[bastien]

r57shell & Nemesis_c
Image link - to our site. And Russian comments.
And credit to "oofwill"? Who is that? I didn't heard about him before.
I hate those, who steals info, and make credits.

Hi r57shell,
I know Oof-will and i also know ivan aka Nemesis_c
please take a look at this link i have also helped ivan for it's custom cartridge with the same solution ^^
http://www.ultimate-consoles.fr/topic/1 ... le-eproms/

Apologize if we relink your schéma ( really better than mine !)
Megadrive fan world is small

[r57shell]

Nemesis_c not ivan.

You can link to our schema but with proper credits.
BTW it supposed to be private schema, it was released in our private section, but someone stole it.

http://www.ultimate-consoles.fr/topic/1 ... le-eproms/

I don't have permission.

[Nemesis_c]

"Ivan" is my account on ultimate-consoles.fr , Bastien (aka X-death) helped me to make the scheme as well as r57shell.
Currently ultimate-consoles.fr site is down for users from Russia (possible sanctions against Russia for saving Donbass people ) and I don't have permission too.
In any case, I put the target schema on the ultimate-consoles site after it has tested. Scheme for 10 MB - I have not tested, so it exists only at me and r57shell.
(Sorry, but I use the Google translator.)

[Nemesis_c]

Hello there,
I have found a schema that allows me to use 2x27c322 but will it work for 3 as well? (Mainly UMK Trilogy)

it will work but only 10 MB