Is it possible to change the built-in game on Sega Master Systems?

[johhnnyD14]

I've seen a few discussion threads about this topic but I have never gotten a definite answer, nor am I willing to risk doing it myself.

Has anyone even attempted this before?

 

[cdamm]

is it even worth the time to do so?

 

[Westcb]

Great example on how not to use the tech support forums... Asking about something that you admit you will not do.

 

[ChopstickSamurai]

Snail Maze 4 Life!

 

[Xian Xi]

BustedStr8 may know. I remember him doing Fix-it-Felix built in games on Genny systems.

 

[johhnnyD14]

BustedStr8 may know. I remember him doing Fix-it-Felix built in games on Genny systems.

Link? That sounds pretty interesting

 

[Apocalypse]

I've seen a few discussion threads about this topic but I have never gotten a definite answer, nor am I willing to risk doing it myself.

Has anyone even attempted this before?

Yes you can. It's quite easy if the game is less than 32kb as you don't need a mapper.
I've made a BIOS with Great Tennis that can also play Japanese card games (they don't contain the "Sega" text at a specific address so they don't pass the OG BIOS check on US/EUR consoles).
For Mark III cartridge games you need an adapter as pinout is different. Easiest option is to use the expansion port on Master Systems 1 as it matches the pinout of Mark III cartridges (no need to swap lines, etc.).

Link to the thread (in French sorry):
http://www.sega-board.fr/viewtopic.php?t=4042&postdays=0&postorder=asc&start=30

 

[chinitosoccer]

The Master System Super Compact made by Tectoy came with either Sonic or Alex Kidd In Miracle World as built-in games, I have seen people mod their MSSC to change between those 2, I don't know if is possible to put other game appart from those.

 

[bustedstr8]

BustedStr8 may know. I remember him doing Fix-it-Felix built in games on Genny systems.

Link? That sounds pretty interesting

Heh...that damn thing. I only did it because I ran out of nice clamshell cases.
I didn't do a write up on it, it was just a sale thread.

I think you could change the game if you inserted the game code at the right address after the bios code and burned a new eprom.

Like Apocalypse said it would have to be a small game since the direct addressing of the SMS is only 32KB. A larger game could be done but it would get messy fast as you would need another eprom, a Sega mapper (from an Afterburner pcb) and also some additional logic to handle /CE of those chips.

 

[johhnnyD14]

Heh...that damn thing. I only did it because I ran out of nice clamshell cases.
I didn't do a write up on it, it was just a sale thread.

I think you could change the game if you inserted the game code at the right address after the bios code and burned a new eprom.

Like Apocalypse said it would have to be a small game since the direct addressing of the SMS is only 32KB. A larger game could be done but it would get messy fast as you would need another eprom, a Sega mapper (from an Afterburner pcb) and also some additional logic to handle /CE of those chips.

What games are less than 32KB?

 

[Apocalypse]

What games are less than 32KB?

All the Sega card games.

 

[johhnnyD14]

All the Sega card games.

So could someone program in Ghost House or My Hero? That would be pretty fascinating

 

[Apocalypse]

So could someone program in Ghost House or My Hero? That would be pretty fascinating

I did it with Great Tennis. No reason it would not work with Ghost house or My hero.

[EDIT]
Link to the Ghost House BIOS tested in an emulator
http://www.filedropper.com/biosghosthouse

 

[donluca]

So could someone program in Ghost House or My Hero? That would be pretty fascinating

Do you happen to still have the Master System Bios with Ghost House mentioned here?
The file is no longer online unfortunately.

Thanks!

 

[Neo Alec]

Never saw this topic back in 2016, but I just think it's cool that it's pointless but possible to do.

 

[donluca]

You can have a BIOS loaded with a diagnostic ROM instead of a game which will make troubleshooting Master Systems much easier as you don't need a flashcart.
Plus, if you have issues with the cartridge connector or the cartridge data lines, you can still diagnose the SMS and discover what's wrong with it.

I'd say that's pretty useful instead of having a game built-in (which you probably have on a cartridge anyway), but, hey, your call buddy.

 

[donluca]

How to make a custom Master System BIOS with any built-in game!

Discover how the SEGA Master System BIOS works so you'll learn to make your own custom BIOS with whatever game or software you want!

donluca.theclassicgamer.net

If anyone is interested, I managed to pull it off on my own (more or less).
Tomorrow I'll probably write a follow-up article with a practical example involving a game.
Hopefully this is enough clear that even people that don't understand Z80 assembly can use to make their own custom BIOS.

 

[donluca]

How to make a custom Master System BIOS with any built-in game!

Discover how the SEGA Master System BIOS works so you'll learn to make your own custom BIOS with whatever game or software you want!

donluca.theclassicgamer.net

Follow up post I've written with some more practical step-by-step examples with actual games.

Hopefully this should be more clear and easy to follow.

I've also included "empty BIOSes" so people can download them and use them to add whatever game they wish.

I won't do any further research on the topic as I think I've explained it well enough about how this all works and it should enable people (even those who've never seen or heard of Z80 assembly) to make their own custom BIOS with whatever game they want.

A major gripe I had with Apocalypse's post above was that he just gave some very vague indication about what to do without including any actual code or reference.
Hopefully my work will fix that.

 

[Moob Butter]

Has anyone even attempted this before?

Just put in a different cartridge bro

/thread