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Embedded flash memory (FLASH) RM0453

118/1450 RM0453 Rev 5

RSSLIB_PFUNC->CloseExitHDP(RSSLIB_HDP_AREA1, 0x8020000);

4.6 Flash memory protection

The main flash memory can be protected against external accesses with the readout

protection (RDP). The pages can also be protected against unwanted write (WRP) due to

loss of program counter context. The write protection WRP granularity is 2 Kbytes.

Apart from the RDP and WRP, the flash memory can also be protected against read and

write from third parties (PCROP). The PCROP granularity is 1 Kbyte.

Part of the flash main memory can be secured, granting exclusive access to this part of the

memory to CPU2.

4.6.1 Readout protection (RDP)

The readout protection is activated by setting the RDP option byte and performing an option

byte programming with OPTSTRT followed by a OBL_LAUNCH, POR or wake-up from

Standby or Shutdown mode. The readout protection protects the main flash memory, the

option bytes, the backup registers (TAMP_BKPxR in TAMP) and SRAM2.

There is no exception while the debugger is connected.

There are three levels of readout protection from no protection (level 0) to maximum

protection or no debug (level 2).

The flash memory is protected when the RDP option byte and its complement contain the

pair of values shown in the table below.

The system memory area is read accessible whatever the protection level. It is never

accessible for program/erase operation.

Level 0: no protection

Read, program and erase operations into the main flash memory area are possible. The

option bytes, SRAM2 and backup registers are also accessible by all operations.

Level 1: readout protection

This is the default protection level when the RDP option byte is erased. It is defined as well

when the RDP value is at any value different from 0xAA and 0xCC, or even if the

complement is not correct.

• User mode

The code executing in user mode (Boot flash) can access the main flash memory,

option bytes, SRAM2 and backup registers with all operations.

Table 18. Flash memory readout protection status

RDP byte value RDP complement value RDP level

0xAA 0x55 Level 0

Any value except 0xAA or 0xCC

Any value (not necessarily

complementary), except 0x55 and 0x33

Level 1 (default)

0xCC 0x33 Level 2

STMicroelectronics STM32WL5 Series User Manual

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