SMS mode on MD/Genesis

elan · Post by **elan** » Wed Sep 26, 2007 11:20 am

Can be used "Sega Master System" mode withouth SMSconvertor /on SMD flashcart/???
I mean homebrew game run on Sega Megadrive/Genesis devCart but in SMS mode...

TmEE co.(TM) · Post by **TmEE co.(TM)** » Wed Sep 26, 2007 3:32 pm

that's impossible without a dongle between the cart and the system unless your flash cart could do it...

8bitwizard · Post by **8bitwizard** » Thu Sep 27, 2007 2:50 pm

I think the cart would have to be specifically made to work in SMS mode, but I'm not going so far as to say it's impossible. It might be possible that if you grounded the M3 select, and interleaved the ROM image to put the Z80 code on every other byte, you could run a non-bankswitched SMS game.

The big problem is that many SMS games used bank switching, which was totally unnecessary on MD/Genesis except for a very few games. So it's not going to be there on a flash cart. And even though most Sega games used esentially the same bank switching scheme, I think there were a few third-party games that used their own bank switching.

So basically an SMS-on-MD multicart is going to need an FPGA to do bank switching, and a menu system that knows which bank switching bitware to download for each game.

ElBarto · Post by **ElBarto** » Thu Sep 27, 2007 5:33 pm

Isn't one of the Phantasy Star is doing this ?

8bitwizard · Post by **8bitwizard** » Sun Sep 30, 2007 1:10 pm

There is a Phantasy Star I cart that works on Megadrive, and it does exactly that. But it still has an SMS bankswitching chip inside. It isn't a generic MD flash cart with an SMS game on it.

Also, the Megadrive doesn't have the TMS-9918A video modes of the SMS, so there are a few SMS games that you can't play. I think F-16 Fighting Falcon is one of them.

elan · Post by **elan** » Tue Oct 02, 2007 8:31 pm

8bitwizard wrote:There is a Phantasy Star I cart that works on Megadrive, and it does exactly that. But it still has an SMS bankswitching chip inside. It isn't a generic MD flash cart with an SMS game on it.

Also, the Megadrive doesn't have the TMS-9918A video modes of the SMS, so there are a few SMS games that you can't play. I think F-16 Fighting Falcon is one of them.

Thank You.So need to have some "bridge" to do that...

elan · Post by **elan** » Sun Oct 07, 2007 9:43 pm

But can I use only ->

- Z80CPU
- TI-PSG soundchip
- MEGADRIVE VDP???

Simply code in Z80 on MD???

Shiru · Post by **Shiru** » Sun Oct 07, 2007 10:32 pm

You can, but you need to make simple startup code on M68K side. And you'll be limited with 8K of RAM and 32K of ROM at once. Whole cartridge will be divided by 32K parts, and you'll be able to switch any of them into top half of Z80 address space (with slow bankswitch code).

elan · Post by **elan** » Sun Oct 07, 2007 10:36 pm

Well for small project is 32KB+8KB enough like little speccy...

Shiru · Post by **Shiru** » Sun Oct 07, 2007 10:43 pm

I think, you'd better to learn M68K basics (it's easy enough), or code in C, which much easier and acceptable for many CPU non-intensive projects. In this case you'll be able to use much more power of SMD than if you will use only Z80 part.

For Z80-only projects, keep in mind that when you want to use more than 32K or ROM, you must place bankswitch code in Z80 RAM, or made tricky jump (because there is only one switchable frame).

8bitwizard · Post by **8bitwizard** » Tue Oct 09, 2007 2:14 am

It is my understanding that you can't use MD video mode (Mode 5) from the Z80 because it needs 16-bit writes.

As for writing Z80 games booted from the 68000, I think there is some hardware (like the joypads) that you can't access, even through the 32K window.

LocalH · Post by **LocalH** » Tue Oct 09, 2007 3:12 am

8bitwizard wrote:It is my understanding that you can't use MD video mode (Mode 5) from the Z80

Yes you can, in SMS mode. Might be different in Genesis mode, dunno.

Mask of Destiny · Post by **Mask of Destiny** » Tue Oct 09, 2007 6:23 pm

8bitwizard wrote:It is my understanding that you can't use MD video mode (Mode 5) from the Z80 because it needs 16-bit writes.

Actually as it turns out both Mode 4 and Mode 5 require 16-bit writes in Genesis mode, but both work fine with 8-bit writes in SMS mode (though I have no idea whether or not Mode 5 DMA works in SMS mode).

elan · Post by **elan** » Tue Oct 09, 2007 7:32 pm

Well It will be better to use 68k I think...
Can I use Snasm68k and older C++ from Borland+some MD LIBS /dev kit/ /older version for MS-DOS/...

ShadowNinja · Post by **ShadowNinja** » Wed Jan 23, 2008 8:52 pm

It could be possible..How did the Power Base Convertor work