I was looking for a solution for MegaCart nvRAM chip which had two problems:
- physically height is large and this presents problems to fit a case
- DS1225 nvRAM has lithium battery and will fail after about 10 years.
I found a relatively new nvRAM chip technology which solves both of these problems.
The chip has two internal 8K memories - 8k SRAM and 8K flash.
Upon power down, an external capacitor provides enough energy for an automated process to start - copy of 8K SRAM to 8K Flash.
When chip is powered up, 8K Flash is automatically copied to 8K SRAM.
I bought a bunch of these chips this week, they arrived on Friday, and have tested for past couple of days and they work great for intended purpose for MegaCart.
The spec sheet indicated data retention of 100 years and chip height is no larger than standard SRAM.
This work also inspired my latest 8K hack cartridge.
With this cart I can save any 8k ROM image to nvRAM, power off and the game/utility will autostart when Vic-20 is powered back up again. It behaves just like a normal auto start cart.
A switch was added to disable chip so Vic-20 can start in Basic and new game/utility could be stored.
Otherwise, I would stuck with same game/utility for the next 100 years
Here is image of completed cart: