Why not just monitor the supply voltage, trigger an interrupt when the crit ical voltage is met during a dropout and save state to flash. It only takes a ms or so to do that. When you detect the drop of the supply voltage, set all peripherals and external circuits to idle, and use only power for the flash storage task
I don't know that it actually has a limit. It's like asking whether type 2 ceramic capacitors have a wear life. (Which they do, in a sense, but that's about aging: time, not cycles.)
I haven't heard if there's actually weird physics that does cause a finite cycle life on very small bits of dielectric.
Well, obviously, you pick a part appropriate for the job. I don't write more than 1/S on average. If you are just using it to store calibration data, it would last "forever". The newer FRAMs have endurances much, much higher, I just don't need it.
The OP said,
Which would make the part ideal, which is why I mentioned it.
I can't tell which way John went on this, but if anyone else has a need for nonvolatile storage with unlimited read/write capability here is a pretty good solution. Looks like they have a 4 kbit and a 16 kbit part.
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Infinite read/write cycles to the SRAM array with EEPROM to back up the SRAM on power fail. 1 millions write cycles on the EEPROM and >200 year retention. "The EERAM works from -40C to 125C and is automotive grade qualified." Beats the hell out of anything using a battery.
Looks like they have some block protect logic for parts of the SRAM array and the chip has three ways to trigger a backup operation. It senses power fail itself and uses a cap to power the backup operation. It can be triggered by an external signal or it can be commanded by software. Backup takes 50 ms.
In a SOIC-8 or TSSOP package it is not very large and is even available in an 8 pin PDIP. The only down side I see it a 5 volt power requirement. Opps, they have 3 volt versions as well! I'm impressed. I wonder if anyone else makes these?
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
The board is still in layout (only about 500 more BGA balls to connect) and I have an SO8 SPI serial flash on the schematic.
We have a microSD card for the main storage, and we found some "high endurance" SD cards, intended for video storage, so we might use the SD as the current-setting backup, with some algorithm that further helps the high-endurance+wear leveling. Or I can stuff a FRAM into the SPI location.
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John Larkin Highland Technology, Inc
picosecond timing precision measurement
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
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