EEPROM on the H7xx would be nice

[n2wx]

I'm not sure how many H7xx applications deploy without EEPROMs. Everything I've touched in the last 5 years in the F3xx and H7xx line needed an EEPROM for the usual customer side configuration persistence requirement. My customers prefer to take the BOM hit for an external EEPROM like the 24C256 or even the weird PCA9500 multiuse I2C device (4 byte pages!) rather than setting things up to possibly exhaust flash words should firmware lose its mind and exhaust the flash area in seconds when used as an EEPROM substitute.

I'm sort of afraid to ask for new things that may tend to break old things but it'd be cool if ST would add a small true EEPROM to the device, maybe not the value line but for the more premium parts with more oomph. 256 bytes should be enough and it's a product ST already makes so....

[n2wx · Accepted solution]

That's a good question. I think the EEPROM emulation has EEPROM like attributes (pages with millisecond-scale write times for ex) that look enough like a real EEPROM I'd be comfy arguing either way. Just glancing at the manual the L1 is superior to a standalone EEPROM since it requires unlocking and has ECC, both features missing from an acceptable standalone 24C256 actual EEPROM.

Another solution that would have worked and I argued for was to use a supercap and the SRAM. Talk about even faster ways to lose data, but at least no risk to the executable. I figured if the 1F supercap was perfect I could count on multi year backup. I didn't need that much. But I got shot down.

[waclawek.jan]

> I figured if the 1F supercap was perfect I could count on multi year backup.

CR2032 is perfect in this regard. If you have to maintain real time, using backup SRAM is then free (as in free beer).

JW

[berendi]

Writing to the first half of EEPROM blocks code execution in bank 0, which is not very EEPROM-like.​

[Uwe Bonnes]

CR2032 imposes transport restrictions, so it needs to be considered carefully.

Using SRAM and having some power reserve and early power failure warning to flash SRAM to dedicated page could also be an option.

[n2wx]

I loved doing stuff with the button batteries - takes me back to the standalone SRAM in the 90s on z80s! - but like you mentioned they're all sorts of shipping issues with them nowadays so I don't bother. It's where the supercap comes in, the 1F seems good for a year - never tried going beyond it - and although it stores a nice bit of energy they're transport friendly. Catching the power going down and flashing with what's left is a good idea. I may try that for the eeprom too - although I have to have 10ms for the thing to do a page write, maybe it's short enough.