Hi,

I use Ramtron FRAM for a long time. There was no problems when our boards have utilized simple parallel FRAM, here: FM1608.
Some months ago we started to use complex Ramtron derivative FM3164. This part contains nonvolatile RAM, RTC, Power SV, Watchdog, Early Pover Fail detector and other features. From this time we have got problems. Some chips after some time of usage fail to write NVRAM permanently, others "lost" their RTC part. In both cases any transitions over I²C bus return NACK at a write phase. There were even cases when once-locked serial number (which is reported as ONCE writeable by set bit SNL) was un-locked or filled with random values. Many times Early Pover Fail detector goes broken - its PFO pin stops to provide interrupt signal.
I wrote to Ramtron some times. They answered that:
"It seems that the PFI/PFO circuit is disabled somehow. And the SNL bit is being set inadvertantly. Both could be due to a Vdd power ramp that causes some strange behavior internally."

But I cannot understand one thing: if this derivative is specially designed to be processor companion with Power SuperVisor built-in so how may it fail from power ramp form???
As for now we look for statistics of fails to understand how to fix this situation.

By the way, Ramtron starts to produce 8051 derivatives:
http://www.ramtron.com/doc/Produ....asp?ID=13

Regards,
Oleg