Master System ROM in a Genesis Repro?

[TheDevil'sCompass]

Has anyone made a Genesis repro with a Master System ROM on it, thus eliminating the need for a powerbase converter? I've checked around but I haven't been able to find any information on how to do this (if it's even possible).

[Steven Pendleton]

There is actually an official game that got released like this: Phantasy Star Fukkokuban.

[TheDevil'sCompass]

That's good news. It's at least possible to do. I located some images of the PCB for Phantasy Star Fukkokuban for the Mega Drive over on SMS Power: https://www.smspower.org/forums/15351-SuccessHelpWithUSBEPROMWriter Now whether or not I can duplicate the work remains to be seen. I'd still like to see a proper schematic if anyone knows of where I can find one.

 

 

[Bruce Tomlin]

I printed out both pictures (with the bottom flipped) and started marking down various signals. I quickly realized that top chip was NOT a 74LS153. (first of all it has 20 pins rather than 16) In fact it is a 315-5342, which is the main chip from the Power Base Converter. Or maybe it's a SMS mapper chip. So in a way, it's cheating.

 

Anyhow, here is a link showing some of the wiring for a PBC:

https://pyra-handheld.com/boards/threads/making-a-power-base-converter.53277/

Edited June 15, 2021 by Bruce Tomlin

[Bruce Tomlin]

Here's some more info on 315-5342:

https://www.smspower.org/forums/9277-AddingFMSoundToMasterSystemModeOnAGenMD

https://web.archive.org/web/20190403192608/http://www.smspower.org/forums/14084-PowerBaseConverterInfo

 

It seems to be a PLA chip that uses "one weird trick" to become an 8-byte ROM that vanishes after the first memory write. It forces opcodes that set the stack pointer to DFFF, then RST 00H onto the bus at startup for the few games that don't initialize the SP properly and expect a BIOS (which the Genesis doesn't have for Z80) to have already done it. So perhaps this was one of the few games that needed it. If this game uses a mapper, it would actually be built into the ROM chip.

 

So it's back to all you need is dealing with the SMS pin remapping, and grounding S_RES (aka M3).

[TheDevil'sCompass]

Great info here. I need to learn more about the mapper chips. I've got a copy of Afterburner for the Master System ordered as this seems to have a good mapper to work with in it. I think to start with this should make a good prototype to figure things out.

[Koa Zo]

There are a few Korean Mega Drive carts that are compilations of Master System games.

[Tanooki]

Hey would it be possible to like reproduce this, yeah I'm talking about a bootleg, with an english translation?

 

Or, given we're talking a combo of a weird PCB with the power base chip, a specific mapper, and then the original SMS rom chip for Pstar, perhaps doing a bypass translated rom chip??

Edited December 30, 2023 by Tanooki

[smds]

I wonder why they include this PLA chip to force the z80 stackpointer to $DFFF instead of just patching the rom 🤔

Maybe they had a ton of already programmed eeproms in stock though...

[Tanooki]

I dunno, but I would love to have one of those carts with an english translation chip attached to it.