[GUIDE] Make a Reprogrammable Genesis Cart

[fatalfuryspecial]

^^ Looks like it's a good thing I asked before trying that out! I was planning on using just a regular old 1MB sized game like sonic 2 or whatever and hooking it up with a 27c800 and a switch like the pictures in your 2nd post of the first page.

So pretty much it just means I need to grab another donor and make separate individual dedicated 1MB and 2x512KB bank switching cart(s)? It's no big deal to make a socketed bank switch cart though right? From your picture it looks like the switch wires are attached to the legs of the eprom; I would prefer to just reprogram the eproms occasionally rather than have a stack of dedicated one-game carts.

thanks for your help!

[Jazzmarazz]

New titles added to the list of battery backed SRAM games.

[FuzzX]

Hi, so many thanks for all your work and information recopilated. I finally read the entire thread so, I got some questions:

Is there any known cartridge of 4MB's with sram save? As I understand, if it exist, and I want to use an 27c322, to put a rom with less from 4 MB's, I should have some way to not let the megadrive access the memory that is not written, is it right?

If it doesn't exists, in the main post sais that with 27c322 A20 must be wired to pin B9, unless is is a saving game in which case it must go for the pin 5 of the 74H00 IC, so, I can't really get lost, but what is B9 pin referred to?


I think this is harder(and maybe, stupid) to answer, but, is there any chance to build a PCB catridge with new components that works with the sega/megadrive?


So many thanks for all your work again, and thank you in advance for your time!

[Jazzmarazz]

Hi, so many thanks for all your work and information recopilated. I finally read the entire thread so, I got some questions:

Is there any known cartridge of 4MB's with sram save? As I understand, if it exist, and I want to use an 27c322, to put a rom with less from 4 MB's, I should have some way to not let the megadrive access the memory that is not written, is it right?

If it doesn't exists, in the main post sais that with 27c322 A20 must be wired to pin B9, unless is is a saving game in which case it must go for the pin 5 of the 74H00 IC, so, I can't really get lost, but what is B9 pin referred to?


I think this is harder(and maybe, stupid) to answer, but, is there any chance to build a PCB cartridge with new components that works with the sega/megadrive?


So many thanks for all your work again, and thank you in advance for your time!

1. What game do you know of that has 4MB's ROM and SRAM?
- It would be possible by locating the SRAM's enable pins after the 4MBs ROM space's enable pins. This is called mapping and refers to the use of that 74HC00 IC. The problem is that the game/program would have to be looking for the SRAM in that exact location. And since most/all official games with SRAM are looking for SRAM at the 2MB space, this could cause problems.

2. "B9" refers to the cart edge, side B, pin 9. The side with the IC's is side B, so look here:

Spoiler warning:

3. I make new PCB's, yes. I have designed several different boards based on different configurations of RAM/ROM. Each one of them was designed with the idea that I can only use "new" and "commercially available" components. See:

Spoiler warning:

The first board is my design with 2MB's ROM and 256KBs battery backed SRAM. With the use of a jumper located in the top left, the user can change the mapping of the board to just 1MB ROm and no SRAM.

The second board is simply a 1MB ROM with no SRAM. The special thing about this board is that it uses two 8-bit ROM ICs rather than one 16-bit ROM IC.

Both of these boards are reprogrammable via the cart edge.

[FuzzX]

Thank you for you fast response! I don't know right now of any ROM that needs SRAM save and ROM size is 4 MB's*. My intention was to make a cart with swappable eproms, that supports the ones with save.

So, if I want to use a donor cartridge with 2 MB's with save, and put a ROM with 4 MB's that doesn't needs save, I should short in some way the SRAM's pins to avoid any problem?

3. I make new PCB's, yes. I have designed several different boards based on different configurations of RAM/ROM. Each one of them was designed with the idea that I can only use "new" and "commercially available" components. See:

Spoiler warning:

The first board is my design with 2MB's ROM and 256KBs battery backed SRAM. With the use of a jumper located in the top left, the user can change the mapping of the board to just 1MB ROm and no SRAM.

The second board is simply a 1MB ROM with no SRAM. The special thing about this board is that it uses two 8-bit ROM ICs rather than one 16-bit ROM IC.

Both of these boards are reprogrammable via the cart edge.

Woah, those pcb's seem very cool, I wish I knew enough electronics to make one with save.



*I just remembered when writting this post, that Sonic & Knuckles + Sonic the Hedgehog 3 is 4 MB's and uses save, but I don't know how it works, since is actually, two games together, I guess it uses battey backed SRAM in one of the two cartridges. So maybe is not possible to save with that kind of ROM.

Thank you so much again for your clarifications!

[Jazzmarazz]

Thank you for you fast response! I don't know right now of any ROM that needs SRAM save and ROM size is 4 MB's*. My intention was to make a cart with swappable eproms, that supports the ones with save.

So, if I want to use a donor cartridge with 2 MB's with save, and put a ROM with 4 MB's that doesn't needs save, I should short in some way the SRAM's pins to avoid any problem?




Woah, those pcb's seem very cool, I wish I knew enough electronics to make one with save.



*I just remembered when writting this post, that Sonic & Knuckles + Sonic the Hedgehog 3 is 4 MB's and uses save, but I don't know how it works, since is actually, two games together, I guess it uses battey backed SRAM in one of the two cartridges. So maybe is not possible to save with that kind of ROM.

Thank you so much again for your clarifications!

Sonic 3 uses FRAM for saving, but that should be mapped to the same location as an SRAM. These two games cannot be put onto one cart alone, so this does not count. It is hacked for use in emulators.

[FuzzX]

Sonic 3 uses FRAM for saving, but that should be mapped to the same location as an SRAM. These two games cannot be put onto one cart alone, so this does not count. It is hacked for use in emulators.

I guessed something like that, since they where one game physically connected with other one.

Getting back to the second PCB you made(two 1 MB IC's with no SRAM), I was thinking about it, and I can't figure out how you made two 8 bit IC's to do 1 MB ROM in total(I keep thinking it should be 2 MB's, not sure if it was some typo). I'm thinking of doing something similar in some sports cartridge(although it will need some insane rewiring if it can be done) or if it can't be done with donor with SRAM, since there's some cheap programmer for 8 bit IC's like the ones you've used. I'm thinking of using that metod to get a 2 MB's ROM compatible one.

Thank you again for your help.

[Jazzmarazz]

I guessed something like that, since they where one game physically connected with other one.

Getting back to the second PCB you made(two 1 MB IC's with no SRAM), I was thinking about it, and I can't figure out how you made two 8 bit IC's to do 1 MB ROM in total(I keep thinking it should be 2 MB's, not sure if it was some typo). I'm thinking of doing something similar in some sports cartridge(although it will need some insane rewiring if it can be done) or if it can't be done with donor with SRAM, since there's some cheap programmer for 8 bit IC's like the ones you've used. I'm thinking of using that metod to get a 2 MB's ROM compatible one.

Thank you again for your help.

The method I used for two 8-bit ROMs is not that complicated. Both 8-bit ROMs are read at the same time as one 16-bit Word (two bytes). Each ROM alone is 512KBytes, for a total of 1MByte. I did have to write a special DOS program (with the help of Colamisu here on EPforums) to break a 16-bit ROM file into two 8-bit ROM files. The Sega reads the high 'byte' and the low 'byte' of a total 'word' from each ROM respectively.So that means half of a line of code is on one ROM and the other half is on the other ROM.

[FuzzX]

The method I used for two 8-bit ROMs is not that complicated. Both 8-bit ROMs are read at the same time as one 16-bit Word (two bytes). Each ROM alone is 512KBytes, for a total of 1MByte. I did have to write a special DOS program (with the help of Colamisu here on EPforums) to break a 16-bit ROM file into two 8-bit ROM files. The Sega reads the high 'byte' and the low 'byte' of a total 'word' from each ROM respectively.So that means half of a line of code is on one ROM and the other half is on the other ROM.

Oh, so, would it be like splitting the rom like this?

Spoiler warning:

e6rnT2b.png

Where the red is the first memory and the blue is the second one?

So, I shouldn't need to trick a 16 bit programmer to do that, isn't it?


I apologize for making so many questions, but i'm new to this kind of electronics.

[Jazzmarazz]

Close. It would be like this:

Spoiler warning:

Attachment 44235

It is easier to understand in binary actually. Consider this:

...ROM0..../....ROM1...
0000 1001 / 1000 0000
This makes up a full 16-bits, which is what the data bus on the Genesis requires.

Here is my schematic:
Take not of the data pins.

Spoiler warning:

[astmin]

heya im new to this and am curious as if i have nfl quaterback club (96 E ) will this be compatible for mega man wily wars (E) i see you where saying you were going to test how did you get on .

[jetblue7]

thanks for this tutorial. best one on the net. has helped me turn many EA carts into useable games.

[icemanxp300]

Hi, I am new to genesis repros. This is my first time trying. I have a GQ-4X True usb. I have an ADP-054 adapter. I am using a m27c160 eprom as it is what I have. I am trying to do Truxton it is 512KBs (4Mbits). I programmed using swap byte. I installed eprom to a board sonic 2 I believe it was. A18 is already connected to b7. I lifted A19 and connected to b8.

When I load the game it glitches and freezes at random. Sometimes the Sega Logo will be glitched. Sometimes it will glitch and free at start screen. If I go fast and press start I can get into game but it glicthes and or freezes within 5 seconds or so. I removed and tried on a hard driven board and rewired A18 and A19 and got same results.

I do not know anything about 8 bit or 16 bit mode? Is there somewhere in the programmer settings for that? I just selected the device "eprom" put my eprom in, selected file, hit swap byte and write. Everything went good but it doesn't work in either board. I have since removed eprom and erased. I am awaiting assistance on what I may have done wrong. Here is a pic of the sonic board and my wire I ran to B8.100_9382.jpg100_9383.jpg

[aries79]

Hi,i have a 512KB donor cartridge and a 27C800 eprom uv how to rewire this? A18 must be wired to pin B7 ???

[Jazzmarazz]

Hi,i have a 512KB donor cartridge and a 27C800 eprom uv how to rewire this? A18 must be wired to pin B7 ???

Yes. A18 is on the eprom and B7 is in the cart's edge.