Backup RAM replacement with FeRAM

[dshadoff]

I was wondering whether anybody here had replaced their backup memory with FeRAM (for example, using Cypress' FM16W08), to allow for savegames to be non-volatile.

From what I can see, one would need to replace the SANYO LC3517B (DIP in the Tennokoe 2; surface-mount in the Duo series), which has a similar but not identical pinout to the 16W08.

Of course, the 16W08 would have 4 times the capacity, so one could either use only 1/4 of it, or create some sort of a system to bank-switch it.
Personally, I'd be aiming for the smallest possible modification so that I can stop losing savegames after periods of inactivity, rather than expanding functionality (but that's just me).

Let me know what has been done, what non-volatile chip(s) you used, and how well it works.

[keithcourage]

Vimtoman did this back when the original pcenginefx forums were still up years ago. I haven't bothered myself.

Here is the link to the thread. www.pcenginefx.com/forums/index.php?topic=20378.msg443656#msg443656

[dshadoff]

Yeah, I saw that and the SRAM/supercapacitor mod... these mods seemed more focused on the expansion of memory than the non-volatile aspect... I also suspect that the complexity (especially the mounting of the controls) is what scared people away.

From appearances, it would seem that only these two people modified their machines, and there wasn't really much follow-up discussion on feedback after using them for a while.

[dshadoff]

In case anybody is interested, I have made some converter boards to replace the memory in Tennokoe 2 units (because they are DIP chips, which are easier).

I have published them in my GitHub repository here: github.com/dshadoff/PCE_FRAM_adapter

I'm still looking into simplifying the surface-mount replacement...

[dshadoff]

I designed a flex PCB to be used when replacing the backup SRAM memory in a Duo with FRAM to make it non-volatile.

It works really well, and it sure beats stringing wires by hand for those pins that don't line up between the former and the latter.
I have published the plans in my GitHub here (the Duo is the SOIC version):
github.com/dshadoff/PCE_FRAM_adapter


The one thing about ordering Flex PCBs is that the minimum fixed cost will cover one unit, or it will also cover close to 100 units... so I have some leftovers.
I thought perhaps modders in here might be interested.  The installation is straightforward except for the removal of the original chip, as it seems to be glued/lacquered to the board.

Also, while I made this for a Duo, it seems likely to fit a Duo-R/RX as well.

I'm happy to answer here any questions about technical aspects of the boards, but if you're interested in obtaining some of my excess, please PM me.

[czroe]

Jul 11, 2020 5:35:37 GMT dshadoff said:

I designed a flex PCB to be used when replacing the backup SRAM memory in a Duo with FRAM to make it non-volatile.
...
The one thing about ordering Flex PCBs is that the minimum fixed cost will cover one unit, or it will also cover close to 100 units... so I have some leftovers.
I thought perhaps modders in here might be interested.
...
I'm happy to answer here any questions about technical aspects of the boards, but if you're interested in obtaining some of my excess, please PM me.

Sending PM.

[bobmoo79]

Jul 11, 2020 5:35:37 GMT dshadoff said:

I designed a flex PCB to be used when replacing the backup SRAM memory in a Duo with FRAM to make it non-volatile.

It works really well, and it sure beats stringing wires by hand for those pins that don't line up between the former and the latter.
I have published the plans in my GitHub here (the Duo is the SOIC version):
github.com/dshadoff/PCE_FRAM_adapter


The one thing about ordering Flex PCBs is that the minimum fixed cost will cover one unit, or it will also cover close to 100 units... so I have some leftovers.
I thought perhaps modders in here might be interested.  The installation is straightforward except for the removal of the original chip, as it seems to be glued/lacquered to the board.

Also, while I made this for a Duo, it seems likely to fit a Duo-R/RX as well.

I'm happy to answer here any questions about technical aspects of the boards, but if you're interested in obtaining some of my excess, please PM me.

Hi dshadoff I'm definitely interested if you still have any available?


Thanks.

[buffalowing]

Jul 11, 2020 5:35:37 GMT dshadoff said:

I designed a flex PCB to be used when replacing the backup SRAM memory in a Duo with FRAM to make it non-volatile.

It works really well, and it sure beats stringing wires by hand for those pins that don't line up between the former and the latter.
I have published the plans in my GitHub here (the Duo is the SOIC version):
github.com/dshadoff/PCE_FRAM_adapter


The one thing about ordering Flex PCBs is that the minimum fixed cost will cover one unit, or it will also cover close to 100 units... so I have some leftovers.
I thought perhaps modders in here might be interested.  The installation is straightforward except for the removal of the original chip, as it seems to be glued/lacquered to the board.

Also, while I made this for a Duo, it seems likely to fit a Duo-R/RX as well.

I'm happy to answer here any questions about technical aspects of the boards, but if you're interested in obtaining some of my excess, please PM me.

Hi dshadoff, when replacing SRAM with FRAM, the existing supercapacitor needs to be removed, right? I read your instruction in your GitHub and I don't recall any mention about it, unless I miss it. Also, when using the existing 5V pin, wouldn't it conflict with the circuit that charge the supercapacitor? I've done Sega Saturn FRAM modification before, I understand it was suggested that 5V source on that console should use another source that is not connected to the battery, to avoid the issue that I mention earlier. Sorry to ask so many questions on my first post in this forum.

[dshadoff]

Strictly speaking, it's not necessary to remove it, and not necessary to keep it.

I don't recall the physical characteristics (i.e. dimensions/location) of the supercapacitor with relation to the SRAM chip, but I don't think that the physical location requires removal in order to place the new chip.
As for the electrical bits, it's true that the FRAM will continue to be powered by the supercapacitor, but that's basically electrically irrelevant too, as it will continue to hold the data after power loss, and there is nothing else powered by the supercap that would starve because of the FRAM's power usage.

This is different from the Saturn, where there is a coin cell which needs replacement from time to time (frequency depends on power drain), and a real-time clock which would compete with the SRAM (or FRAM) for the battery's power.

I tend to leave things as-is unless they are causing some sort of harm... but there is still one reason you might want to consider removing the supercapacitor. If the part were to degrade to the point where its electrolyte leaks, there is a possibility that it could damage PC board traces. However, I'm not sure whether the supercap's electrolyte resembles the electrolytes of aluminum capacitors in this way.

[buffalowing]

Jul 13, 2022 20:29:27 GMT dshadoff said:

Strictly speaking, it's not necessary to remove it, and not necessary to keep it.

I don't recall the physical characteristics (i.e. dimensions/location) of the supercapacitor with relation to the SRAM chip, but I don't think that the physical location requires removal in order to place the new chip.
As for the electrical bits, it's true that the FRAM will continue to be powered by the supercapacitor, but that's basically electrically irrelevant too, as it will continue to hold the data after power loss, and there is nothing else powered by the supercap that would starve because of the FRAM's power usage.

This is different from the Saturn, where there is a coin cell which needs replacement from time to time (frequency depends on power drain), and a real-time clock which would compete with the SRAM (or FRAM) for the battery's power.

I tend to leave things as-is unless they are causing some sort of harm... but there is still one reason you might want to consider removing the supercapacitor. If the part were to degrade to the point where its electrolyte leaks, there is a possibility that it could damage PC board traces. However, I'm not sure whether the supercap's electrolyte resembles the electrolytes of aluminum capacitors in this way.

dshadoff, thanks for responding me so quickly! I did have concern with potential leakage from the supercapacitor, although I never heard people have them leaking like og XBOX clock supercapacitor...

[keithcourage]

I have only come across one bad super capacitor and I've worked on thousands of DUOs. The capacitor didn't even leak when it was bad. It just simply wouldn't hold a charge for long.

Lots of people replace the super capacitor out of fear of it going bad or leaking but I'll tell you it's the last part anyone should worry about inside a DUO as they last a very very very long time.

Now that I think about it, I haven't found a bad one inside a PCE Docking station either and those are 4-5 years older than most DUOs.