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my working knowledge of electrical engineering is quite limited, so please excuse me if my question has been answered under different terminology!

I was looking at old Gameboy games, which require a CR1616 battery to keep their saved games, and then I noticed how cartridges for the N64 variously used the volatile memory in early releaes and EEPROM non-volatile memory in later cartidges, as weel as later era Gameboy Advance cartridges and pretty much any modern solid state memory, thumb drives all that do not require a current to keep the data.

So Is it possible, or plausible, to take an old Gameboy cartridge requiring the CR1616 cell and replace it's memory with something non-volatile in the average hobbyist's home workshop?

I do not intend to do this, I only ask if it is possible to replace only the save memory keeping all the rest of the original hardware intact. I am aware there are many ways to accomplish something similar, such as an adapter for SD cards and then running some sort of emulation, but that is too un-original (hardware wise) for what I am thinking.

Thanks for any input folks!

Edit: If memory is memory (so long as the capacity is recognized by the system using it), and memory with a compatible number of pins isn't able to be acquired, would some fancy soldering be a way to either bridge or split pins from the IC to the board of the cartridge?

Edit 2: It appears that what I am talking about is replacing "SRAM" with "nvSRAM". Not much help to me, but at least I understand some terminology better.

Also, here is aq link to the inside of the exact cartridge I had in mind when thinking about this question: https://en.wikipedia.org/wiki/ROM_cartridge#/media/File:PokemonSilverBoard.jpg

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  • \$\begingroup\$ Can you find which memory ICs where in use? It's far within a resonable possibility there is a pin compatible replacement for it if the same chip has been used elsewhere in the industry. \$\endgroup\$ – winny Jan 21 '17 at 11:16
  • \$\begingroup\$ I do not actually have any of said cartridges right now, so I would be hard pressed to identify what ICs are used, but that actually brings to mind an ancilliary question which I will add to an edit of my original question. \$\endgroup\$ – Ben Jan 21 '17 at 11:19
  • \$\begingroup\$ Not so. I'm sure the information is available on the Internet. If uncommon/proprietary, it will ne a lot of work. If common it might be a direct drop in replacement. \$\endgroup\$ – winny Jan 21 '17 at 11:36
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    \$\begingroup\$ People appear to have built cartridges with FRAM: tindie.com/products/JRodrigo/flash-cart-2mb4mb-for-gameboy- ("infinite" data retention, RAM-like write speed) \$\endgroup\$ – pjc50 Jan 21 '17 at 12:27
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As long as your EEPROM has sufficiently fast IO, I don't see why not. The nvSRAM option is also a possibility, although they're certainly not common parts and you'd likely run into similar design problems as an EEPROM.

The primary problem would be the fact that any replacement IC is unlikely to have the same electrical interface as the traditional volatile memory, but you could emulate that using a microcontroller or perhaps a small CPLD as an intermediary translator.

Another way to do it is to engineer a completely new cartridge which emulates the behaviour of the original but with modern parts of your choosing. There are commercial products (e.g. the Everdrive GB) which do this so that you can load ROM files off of an SD card.

The hardware of the Gameboy has been documented extensively by hobbyists, so you can easily look up how the interface works in exquisite detail.

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  • \$\begingroup\$ I am aware of the emulators like Everdrive you mentioned, but those are too different to the original product. It lacks the "nostalgia factor" that was in mind. I know its silly, but I have collectors in mind that my idea might appeal to; Logic has little bearing on them! The most hardcore would even deny that relatively minor modification, but I think if that was the only change to original hardware (minor, yet MAJOR in it's impact, saving games indefinitely), then many purists may accept it as the only suitable modification, if you know what I mean? \$\endgroup\$ – Ben Jan 21 '17 at 11:50
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Battery backed SRAM can be read and written on an individual location basis at full bus speed. Indeed some games use part of the cart ram as extra workspace and other parts as save space.

Flash on the other hand is written in blocks, typically involving a special sequence of operations and relatively long waits. Games that use flash for saving need to deal with this. So a modification that changed a game from battery backed SRAM to flash would require either modifying the game code or adding an intermediate ram buffer in the cart with an active process to copy it.

There is however a niche memory technology called "FRAM" made by cypress semiconductor (formerly ramtron). Fram is non-volatile but has SRAM like access behavior and is fast enough to sit directly on the bus of something like a gameboy. I can find links to gameboy flash carts that use FRAM in place of SRAM and I suspect with a bit of effort an interposer board could be made to allow replacement of the SRAM in an original cart with FRAM.

Note however that while FRAM has much better write endurance than flash it's endurance is still limited. If a game hammers the cart ram with constant writes to the same location this may limit the life of a FRAM based cart. In partice I doubt this will be a big problem though. It also seems to be rather expensive with mouser wanting £12 a shot in singles (a bit less in volume but still more than £8 a chip at the highest price break they list) for the smallest parallel FRAM chip.

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