New product will have multiple axes of motion and nothing but quadrature encoders and home flags on all but one of them, that is most axes have no absolute position indicator of any kind. Adding expensive absolute position encoders is not an option, cheap ones like potentiometers with A/D converters are out for reliability reasons.
So on a power-up, the motion control system has no way of knowing for sure where most axes are.
Once the system has homed all the axes, positions will be kept updated by the quad encoders some number of times per second, but I'm concerned about the situation at power-up. If I could could continuously capture the latest position updates in non-volatile storage, I'd have a reasonable starting point after power is cycled.
EEPROM or flash do not seem fast enough to keep up in real time, and life span could be an issue.
In another product some years ago we used a combination RAM/EEPROM chip that looked like an 8-bit wide static RAM, but had built-in power monitoring circuitry. Given a slow enough fall time on the power supply, it automatically write protects itself and shadows the RAM into EEPROM when power goes off, then copies the EEPROM back into RAM at power-up. No processor overhead whatsoever.
I could use something like that, but I was wondering if anyone else has suggestions for something that has reasonable RAM access times under ordinary circumstances, but transparently preserves stored values without power.
I'd only need something with a few hundred bytes of storage. I'd like to find something in the $5.00 USD range (500 - 1K quantities), but I could probably go up to $10.00 for the right part.
All suggestions gratefully accepted.