31.2.1 EEPROM Write Prevents Writing to SPMCSR

Note that an EEPROM write operation will block all software programming to Flash. Reading the Fuses and Lock bits from software will also be prevented during the EEPROM write operation. It is recommended that the user checks the status of the EEPE bit in the EEPROM Control Register (EECR.EEPE) and verifies that the bit is cleared before writing to the SPMCSR Register.