Replacing SRAM chips - help needed

[Xaranar]

Hi all

So recently I've been experimenting with ways to eliminate the need for batteries on various hardware that uses them to keep save games. I first had the idea when I opened up an N64 Controller Pak, and to my surprise, rather than flash memory used by the PlayStation, Nintendo opted for a volatile SRAM chip with a battery to keep data intact. Now, it being the future, I wanted to know if there existed a way to replace that chip for something non volatile, and eliminate the battery altogether. As it turns out, the SRAM chips used on those memory cards, are usually something akin to the LH52256 - a 256kb chip, and to my surprise, there exists a completely pin compatible 256kb non volatile FRAM chip, designed as a drop-in replacement - the FM18W08. This actually works like a charm, and that memory card no longer requires a battery. So after this, I wondered about other things that use volatile SRAM and a battery, so I cracked open a couple of my SNES cartridges, Super Mario RPG and Yoshi's Island to be precise, and lo and behold, both of these games also use some variant of the LH52256. Naturally, I swapped these chips out and inserted an FM18W08 in their place, expecting similar results, however, sadly this was not the case. I have read on this guy's blog that he has had success when doing something similar with other SNES games, albeit with lower capacity chips, but with 256kb FRAM chips, both Yoshi's Island and Super Mario RPG crash on startup and do not run.

Anyway, after all that, does anyone have any ideas about how I might be able to get this working? Thanks!

[pyroman512]

I recently found this place. I haven't replace any of my stuff yet but it seems promising for what you are trying to do.

http://www.customretrostuff.com/games-- ... for-snes-/

[Xaranar]

Yeah, that's actually the blog I linked to in my original post

Whilst his information is good, he doesn't seem to include specific information for 256kb chips, and that's where I'm having the issue.

[pyroman512]

Ahh my bad I didn't see the link before.

[leonk]

CR2032 are cheap - After 25 years many are still working in NES carts. Why try to reinvent the wheel?

[Xaranar]

Because I want a more permanent solution. And because I can.

[leonk]

Because I want a more permanent solution. And because I can.

I lost track of how many CR2032's I replaced at this point. I buy the battery holders in packs of 100, and given how often I order them I would guess a bit north of 3000. I've never had an issue.

But if you still want to persuit a complete replacement, I'd make sure the IC's are rated for 5V operation and are 150ns or faster.

Make sure also the inplimentation is not like what they did with CDi where a watch battery is actually embedded in the substrate! Fun times getting that out for replacement.

[mvsfan]

the backup battery in games lasts a VERY long time. I have several NES games with the original battery that still save.

What would really need one of these projects though? the Sega Saturn. I Usually end up replacing the battery in the console every year or so.

[Star1]

the backup battery in games lasts a VERY long time. I have several NES games with the original battery that still save.

What would really need one of these projects though? the Sega Saturn. I Usually end up replacing the battery in the console every year or so.

http://db-electronics.ca/2017/02/10/seg ... -required/

If you weren't already aware, such a a project has already been done

[Einzelherz]

the backup battery in games lasts a VERY long time. I have several NES games with the original battery that still save.

What would really need one of these projects though? the Sega Saturn. I Usually end up replacing the battery in the console every year or so.

http://db-electronics.ca/2017/02/10/seg ... -required/

If you weren't already aware, such a a project has already been done

I certainly wasn't and now I'm hankering to brick my Saturns

[Xaranar]

I've successfully done this on an N64 controller pak, and my Mega CD model 2, a straight up swap was enough. With SNES carts on the other hand, it doesn't seem to work and I have no idea why.

[mvsfan]

well... that mod will save your games even if the battery dies, but you still will have to reset the clock n shit. what good is that? resetting the clock is the most annoying feature of the saturn!

seriously, thanks for pointing this mod out. will try it someday.

[Xaranar]

So I did some digging, and it turns out qwertymodo had a crack at this some 5 years ago, and succeeded no less. I found an old thread of his on the Ben Heck forums, and he worked out that the CS pin wasn't being driven correctly on the FRAM chip by the SNES cart PCB. He mentions that in order to drive the CS pin, the logic needs to be CS_IN = CS_OUT | (RD & WR), where CS_IN is the CS pin on the chip, and CS_OUT is the CS signal from the cartridge. In order to get this, the logic needs to be CS_IN = (CS_OUT NAND CS_OUT) NAND (RD NAND WR). Ordered myself some NAND logic gates and I'm going to give it a go.

[Riplike]

Hi Xanar
Have you successfully converted the logic? If so, could you please tell me how to do it to the logic gate? I am totally new to this type of project and I am in desperate need of help for some tutorials. Thanks a lot