Hi,
First of all it is necessary to understand FSEC and FPROT features.
FSEC is not possible to be changed. FPROT can be changed in the way only to increase protection but this is valid till next reset if it is done from outside just by modifying FPROT because after reset the FPROT is loaded from flash again.
I do not understand why they want to change security and protection for loaded MCU.
If the MCU is secured then there is no possibility to access these registers.
Moreover, I'll use info from the reference manual:
All bits in the FSEC register are readable but not writable. During the reset sequence, the FSEC register is loaded with the contents of the Flash security byte in the Flash configuration field at global address 0x3_FF0F located in P-Flash memory (see Table 24-4) as indicated by reset condition F in Figure 24-6. If a double bit fault is detected while reading the P-Flash phrase containing the Flash security byte during the reset sequence, all bits in the FSEC register will be set to leave the Flash module in a secured state with backdoor key access disabled.
The (unreserved) bits of the FPROT register are writable with the restriction that the size of the protected region can only be increased. While the RNV[2:0] bits are writable, they should be left in an erased state.
During the reset sequence, the FPROT register is loaded with the contents of the P-Flash protection byte in the Flash configuration field at global address 0x3_FF0C located in P-Flash memory (see Table 24-4) as indicated by reset condition ‘F’ in Figure 24-13. To change the P-Flash protection that will be loaded during the reset sequence, the upper sector of the P-Flash memory must be unprotected, then the P-Flash protection byte must be reprogrammed. If a double bit fault is detected while reading the P-Flash phrase containing the P-Flash protection byte during the reset sequence, the FPOPEN bit will be cleared and remaining bits in the FPROT register will be set to leave the P-Flash memory fully protected.
Trying to alter data in any protected area in the P-Flash memory will result in a protection violation error and the FPVIOL bit will be set in the FSTAT register. The block erase of a P-Flash block is not possible if any of the P-Flash sectors contained in the same P-Flash block are protected.
Best regards,
Ladislav
