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Soniccd123
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A Sega Genesis repro PCB with FeRAM support

by Soniccd123 Fri Jul 31, 2020 1:31 pm

Hello,

I'm a old time reader of racketboy but never posted anything. I've been comunicating with Ziggy587 about his thread http://www.racketboy.com/forum/viewtopic.php?f=56&t=36353, i noticed a lack of cartridge PCBs projects available online for Sega Genesis with save support here and everywhere and also schematics explaining how do they work.

I know that there are ready made PCBs for sale with this purpose but often, for non US residents, they are quite expensive, with PCBs production services being considerably cheaper. Also, this is not a versatile solution considering the needs of each individual

So, with lots of time in my hands thanks to COVID-19, i've decided to build my own cartridge with saving capabilities and make it open and available for the online comunity, thinking about modding possibilities this opens and also to improve my design if needed, as i'm not a engineer, just a amateur who likes electronics.

I also dislike battery backed saves (thats a very personal opinion based on some bad past experiences lol) so i've decided to buid the cart based of non volatile FeRAM. I know this may be not ideal for some people, but as the project is open, this can be easily modified for battery SRAM use.

Finally, here it is: https://github.com/soniccd123/Genesis-FeRAM-Cart

It uses a 27C322 32Mb UV EPROM as the main ROM, a FM1808 256Kb FeRAM for saving and some glue logic. All was designed using KiCAD and can be easily modified for other ROM and RAM types as needed. I've also included a rudimentary DIP switch based bank switching circuit for the possibility of burning multiple files to the ROM. I've already built some units and it works in real hardware with no problems.

I hope this can be useful for someone, i'm open for feedback if any problems arrive and be welcome to make modifications to the board as needed.

Soniccd123

Edit: The gerber files for producing the board are included in the GitHub project.
Last edited by Soniccd123 on Fri Jul 31, 2020 2:46 pm, edited 1 time in total.
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Ziggy587
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Re: A Sega Genesis repro PCB with FeRAM support

by Ziggy587 Fri Jul 31, 2020 1:45 pm

Awesome, thanks so much for sharing this!

I haven't had a chance to look at the schematic yet, but does the dip switches control the ROM and the RAM? Or just the ROM?
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My Sale Thread - I am selling around three quarters of my video game collection as well as some other odds and ends!

I want to buy Universal Game Cases, if you have any spares please PM me! I'm looking to only deal with members that have good BST feedback on this forum.
Soniccd123
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Re: A Sega Genesis repro PCB with FeRAM support

by Soniccd123 Fri Jul 31, 2020 2:37 pm

Ziggy587 wrote:Awesome, thanks so much for sharing this!

I haven't had a chance to look at the schematic yet, but does the dip switches control the ROM and the RAM? Or just the ROM?


For now just the ROM, it is possible to control the RAM also, but this needs some thinking, maybe use two DIP switches?
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Ziggy587
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Re: A Sega Genesis repro PCB with FeRAM support

by Ziggy587 Fri Sep 04, 2020 8:35 am

Hey Sonniccd123, I had a couple of questions about this board. I finally got around to taking a look at it with a gerber viewer and noticed that there aren't any silk screen value identifiers and I didn't notice a BOM. What are the two ICs for U1 and U3? Is R1-R4 just pull up or down resistors for address lines? What is the purpose of JP1 on the back?
Image

My Sale Thread - I am selling around three quarters of my video game collection as well as some other odds and ends!

I want to buy Universal Game Cases, if you have any spares please PM me! I'm looking to only deal with members that have good BST feedback on this forum.
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fastbilly1
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Re: A Sega Genesis repro PCB with FeRAM support

by fastbilly1 Fri Sep 04, 2020 7:48 pm

I wasnt planning on making any Genesis carts ever, but now I am very interested. Thank you Soniccd123
Soniccd123
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Re: A Sega Genesis repro PCB with FeRAM support

by Soniccd123 Wed Sep 16, 2020 11:15 pm

Ziggy587 wrote:Hey Sonniccd123, I had a couple of questions about this board. I finally got around to taking a look at it with a gerber viewer and noticed that there aren't any silk screen value identifiers and I didn't notice a BOM. What are the two ICs for U1 and U3? Is R1-R4 just pull up or down resistors for address lines? What is the purpose of JP1 on the back?


Hey, thanks for pointing that! I had totally forgot it ::facepalm::. Will update the project with these informations.

I was testing some games and noticed that 2MB ou less ROMs did not properly identified the FeRAM, JP1 is a jumper to select if you're using a ROM bigger or smaller than 2MB.

U1 is a 74HC74 D-Type Flip-Flop
U3 is a 74HC139 2 to 4 demultiplexer
The resistors are all pull-up, i normally use 1K to each;

I'll add everything in the project and original post.

Thanks again for the insight.

PS: Did the schematic opened correctly in your PC? Just to know if i need to do any modifications.
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Ziggy587
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Re: A Sega Genesis repro PCB with FeRAM support

by Ziggy587 Thu Sep 17, 2020 10:02 am

Soniccd123 wrote:For now just the ROM, it is possible to control the RAM also, but this needs some thinking, maybe use two DIP switches?


Hmm, you could use two DIP switches, but would that divide the RAM into too small of chunks for saves? I'm not big on Genesis, I don't know the typical save file sizes. Another option would be to use the same 4 DIP switch, but control only 2 address lines for ROM and then 2 address lines for RAM. Although, not many Genesis games use game saves. One might make a multi cart where only 1 of the games requires saves.

Soniccd123 wrote:Hey, thanks for pointing that! I had totally forgot it ::facepalm::. Will update the project with these informations.


Thanks!

Soniccd123 wrote:I was testing some games and noticed that 2MB ou less ROMs did not properly identified the FeRAM, JP1 is a jumper to select if you're using a ROM bigger or smaller than 2MB.


I see. For games that were 2MB or less, did you mirror the ROM to fill the 27C322 or just leave it blank?

Soniccd123 wrote:PS: Did the schematic opened correctly in your PC? Just to know if i need to do any modifications.


I loaded the gerber files with KiCAD's gerber viewer and that worked fine. When I tried to load the schematic in KiCAD, I got an error that my version of KiCAD was not support. I guess I have an older version of KiCAD on my Linux laptop. I've only used Eagle before, but I've been wanted to also learn KiCAD. When I get a chance, I'll install the latest version of KiCAD and see if it works.

Thanks again for sharing this!
Image

My Sale Thread - I am selling around three quarters of my video game collection as well as some other odds and ends!

I want to buy Universal Game Cases, if you have any spares please PM me! I'm looking to only deal with members that have good BST feedback on this forum.
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