drkzrg / pce_fram_adapter

Adapter for easily replacing your PC Engine's backup memory with non-volatile FeRAM

FRAM converter boards

The PC Engine series of systems has a different game-save storage system than most people these days have gotten used to. It used a 2KB static RAM. This wasn't in the cartridges themselves; initially, it was sold as pat of an add-on to the system: The Tennokoe 2, "Voice from Heaven". In later systems like the Duo series, it would be integrated into the system unit, yet still be limited to 2KB static RAM.

You're probably thinking, "Static RAM is volatile - it loses its contents when the power is shut off", and you'd be right. There really weren't any non-volatiole options at the time. Instead, they used batteries or large capacitors to apply continuous power to the memory, so that it would not lose its contents. In the case of the Tennokoe 2, 2 "AA" cells were used; in the case of the Duo, a large capacitor was used.

I have lost a few game saves on my Duo because I failed to turn the system on for a period of time long enough to lose its contents... probably about 1 to 2 weeks.

Because of this, I was inspired to replace the SRAM with modern FeRAM to make it non-volatile. But the Duo is a tighter-packed PC board with surface-mount chips, so I felt it was easier to first test the idea on the Tennokoe 2, which uses a DIP SRAM chip.

I have followed up with a design for a flex PCB to use with surface-mount chips in order to be suitable for my Duo, and it also works well.

I chose to use the Cypress FM16W08 chip, which can handle 5V, has timing which is equal to or better than the SRAM it is replacing, and has a similar pinout. But I still needed to make adapter boards (which is what this repository is all about).

As the FeRAM is rated for 100 trillion read/write cycles, there is no concern about lifetime under the usage in this application.

I designed the boards using the free version of EAGLE (2-layer, less than 100mm on both X- and Y-axes). The gerbers are included in this repository, in case you want to get your own set made.

Assembly/installation instructions for the FRAM-DIP board for the Tennokoe 2:

https://github.com/dshadoff/PCE_FRAM_adapter/blob/master/FRAM-DIP-assembly.md

Assembly/installation instructions for the FRAM-SOIC board for the Duo and other machines:

https://github.com/dshadoff/PCE_FRAM_adapter/blob/master/FRAM-SOIC-assembly.md