Making SEGA Genesis cartridges

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nitrogen_widget:
sweet.

bobbyb13:
I don't even play console games and i love this project.

Teach me more!

pbj:
I shouldn't probably comment on how many hours this took me to figure out, but here we are.

Basically, to my understanding, SEGA used these ROMs:

M27C400 - 512KB
M27C800 - 1 megabyte
M27C160 - 2 megabytes
M27C322 - 4 megabytes

M27C400 is only 40 pins, so it is shifted one slot over on the PCB. That means pin 1 on the chip is plugged into pin 2 on the PCB. It does not have A18 or A19.

M27C800, M27C160, and M27C322 are 42 pins.

M27C800 does not have A19. The pin is physically there and I think it's tied into 5V. You have to cut this 5V connection and connect the pin to B8 if you want to use a bigger chip.

M27C160 has A19 and it's connected to B8 on the cartridge connector instead of the 5V line. I think this is the most common PCB/ROM arrangement.

M27C322 has A20, it's on pin 32. This needs to be tied into B9 on the cartridge connector. If the board didn't originally have this ROM on it, this pin is connected to 5V and this needs to be cut.

So, unlike other consoles, Genesis ROMs don't care which chip they're burned to. You just have to alter the PCB so that the console knows how to address the chip.

I have been very frustrated with the documentation I've found on line about all this. Blurry photos and fuzzy memories. So, I hope this is a little more clear. At least it'll be good notes to myself some day, maybe.

If you make the connections as shown in the photo, you can make any board work with any ROM. The only exception are the games bigger than 2MB with saves. It has to be split across 2 2MB chips without significant reworking of the PCB and additional components. 2MB of the ROM on the chip on the bottom of the board, the rest on the top. There's only a handful of these games and World Series Baseball 95 and 96 make excellent sacrificial lambs to become Beyond Oasis and Phantasy Star 4. I'll post more information about these after I make one.

:cheers:

Mike A:
Have you considered a Pi?

Malenko:

--- Quote from: Mike A on March 29, 2022, 06:21:37 pm ---Have you considered a Pi?

--- End quote ---
BUY A KADE!

Also great work. I am assuming the rom didnt need split on my beyond oasis cart cause the Chinese bootleggers just designed a PCB that allows for a 4MB ROM and battery? I didnt crack it open to look but now I think I will.

ok, heres the guts of the Beyond Oasis bootleg:

This is still one of the best genny games

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