Erik:
Please read my post as the first reply on this thread. The CRC helps you determine which of several copies of your data is GOOD. The concept is that only one copy of the data would be corrupted if you lose power during the save to the EEPROM or a battery backed up RAM.

In a real system working copies of the parameter set, counters, accumulators or whatever they may be are kept in regular internal RAM of the 8052. When something changes then you calculate the new XOR crc and write the updated information to EEPROM.

In the case of a non-volatile set of user parameters it is typically OK to just do the updates as the user has made changes becasue at 100,000 or 1 million cycles you worry more about the user wearing out the keypad than the EEPROM. In the case of automatic repetitive update, such as the counters I describe in the previous post, you need to manage the updates to avoid wearout.

Please don't be negative about the concept of the CRC. If you store 2 or 3 copies and then use CRC to validate which copy is GOOD then you are in business!! This scheme is in use in several dozen embedded products I have developed over the years and works very well. I am just trying to help others see that there are workable ways to store nonvolatile data in cheap components like 93C46. Certainly for many applications it is WAY better than putting a backup battery!!!

I can post sample code that implements the concept if people express an interest.
Mike