Before I dismantle one, I don't suppose anyone knows where I can find some hi-res images of the VMU circuit board? I'm interested in the traces so they have to be pretty clear. I've had a quick look around and haven't found anything. Or even better, has anyone digitized the PCB?
Back https://i.warosu.org/data/vr/img/0007/76/1370808059666.jpg Front https://i.warosu.org/data/vr/img/0007/76/1370807853927.jpg
The potato chip is based on the LC8610, here's a datasheet on the processor: http://pdf1.alldatasheet.com/datasheet-pdf/view/41059/SANYO/LC86104C.html I couldn't tell you how they stuffed the extra ram in there. It has to be same type of non volatile memory. At least I think I remember my VMU keeping my saves when I replaced the batteries.
Really only 168 bytes of ram? is that where the saves are stored? I have one of those multi page VMU memory card where it has banks of switchable memory, I'll have to take a look inside to see what memory it has and how it's setup.
The Sega chip is "based" off of the LC8610. The instruction sets are very similar, with the potato having a couple extra commands.
A VMU has 128 kiB of flash (non-volatile) memory. Normally 28 kiB are reserved for system use, but you can unlock 22 more kiB with a homebrew program, thus getting a total of 122 kiB or 244 blocks available. That's only 1/10th of a floppy! My guess would be that the ram is the one used by the potatio chip to do calculations, run the VMU menus, copy, etc. FG
