Sequence for Execution of Self-Programming

In order to execute self-programming (the execution of writes to the NVM controller’s command register), the following steps are required:

  1. 1.The software temporarily enables self-programming by writing the SPM signature to the CCP register (CPU.CCP).
  2. 2.Within four instructions, the software must execute the appropriate instruction. The protected change is immediately disabled if the CPU performs accesses to the Flash, NVMCTRL, or EEPROM, or if the SLEEP instruction is executed.

Once the correct signature is written by the CPU, interrupts will be ignored for the duration of the configuration change enable period. Any interrupt request (including non-maskable interrupts) during the CCP period will set the corresponding Interrupt flag as normal, and the request is kept pending. After the CCP period is completed, any pending interrupts are executed according to their level and priority.