9.3.3 Preventing Flash/EEPROM Corruption

During periods of low V_DD, the Flash program or EEPROM data can be corrupted if the supply voltage is too low for the CPU and the Flash/EEPROM to operate properly. These issues are the same as for board level systems using Flash/EEPROM, and the same design solutions should be applied.

A Flash/EEPROM corruption can be caused by two situations when the voltage is too low: First, a regular write sequence to the Flash requires a minimum voltage to operate correctly. Also, the CPU itself can execute instructions incorrectly when the supply voltage is too low. See the Electrical Characteristics chapter for Maximum Frequency vs. VDD.

Flash/EEPROM corruption can be avoided by these measures:

Keep the device in reset during periods of insufficient power supply voltage. This can be done by enabling the internal Brown-Out Detector (BOD).

The voltage level monitor in the BOD can be used to prevent starting a write to the EEPROM close to the BOD level.

If the detection levels of the internal BOD does not match the required detection level, an external low- VDD-reset protection circuit can be used. If a Reset occurs while a write operation is ongoing, the write operation will be aborted.