Write Protections; Table 11. Access Versus Read Protection Level; Figure 5. Rdp Levels - ST STM32F423 Reference Manual

Embedded Flash memory interface
--
Memory area
Main Flash Memory
Option Bytes
OTP
1. The main Flash memory is only erased when the RDP changes from level 1 to 0. The OTP area remains unchanged.
Figure 5
3.6.4

Write protections

Up to 16 user sectors in Flash memory can be protected against unwanted write operations
due to loss of program counter contexts. When the non-write protection nWRPi bit
(0 ≤ i ≤ 14) in the FLASH_OPTCR registers is low, the corresponding sector cannot be
erased or programmed. Consequently, a mass erase cannot be performed if one of the
sectors is write-protected.
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Table 11. Access versus read protection level

Debug features, Boot from RAM or
Protection
from System memory bootloader
Level
Read
Level 1
Level 2
Level 1
Level 2
Level 1
Level 2
shows how to go from one RDP level to another.
Write Erase
(1)
NO NO
NO
YES
NO
NO NA
NO NA

Figure 5. RDP levels

RM0430 Rev 8
Booting from Flash memory
Read Write
YES
YES
YES
NO
YES
YES
RM0430
Erase
NA
NA