Theory Of Operation

The purpose of the diagnostic is to detect if the Electronic Erasable Programmable Read Only Memory (EEPROM) data has been corrupted or access to the data is not possible anymore. If the access is not possible anymore the Flash Control Unit (FCU) Application-Specific Integrated Circuit (ASIC) sets a hardware failure. The corruption of the data is detected by calculating a checksum and comparing it to a reference value. The EEPROM includes all data that can change from transmission to transmission but has to be stored in non-volatile memory (e.g. fault memory, customer specific data such as part numbers, etc). The physical EEPROM emulation memory in flash is sub divided into several sector groups. Each sector group holds one set of data that was stored at the moment of an update. If all sector groups are filled, the sector group with the oldest set of data is used for the update. Updating the sector group results in erasing the entire sector group memory and then programming the current data to it. To always ensure a valid backup of the EEPROM data, at least 2 non-defective sector groups are needed. Each sector group is checksum protected and the validity of the checksum is verified before reading and after writing the data.