Michael Braithwaite

QY4 Flash Memory Content Corrupted

Discussion created by Michael Braithwaite on Nov 14, 2006
Latest reply on Mar 22, 2007 by Gordon van den Broek
I am using MC68HC908QY4CDW in my products( the date code is XAB0526). I experienced field return units problems. The return units failed start up. It will resume work properly after I reprogram them. Obviously, the content of flash memory has been corrupted, but the user code never call the ROM-resided code to either erase, or write any contents of the flash memory.
I contacted at support@freescale.com a few month ago. I was advised with below suggestions, (1) protect the whole flash memory by programming FLBPR with all zeros. (2) shielding the MCU.
After I programmed the FLBPR with all 0s, some units still failed after a few thousands time of power ON and Off cycles. (Due to the physical constraint of the PCB board, we didn’t employ the shielding solution) 
In my application, no external reset and brown out circuit are used and the LVI reset function was DISABLED so that the MCU can poll the LVI to implement other functions.  After I enable the LVI reset function and programmed the same failed units, I have not witnessed  the units fail by cycling the power for more than 10,000 times.
My question is if this problem can be eliminated by enabling the LVI reset, is there any possible reasons that may cause the flash corrupted?  
Any thoughts or suggestions are welcome.