RM0440 Rev 4 119/2126
RM0440 Embedded Flash memory (FLASH) for category 3 devices
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3.5 FLASH memory protection
The Flash main memory can be protected against external accesses with the Read
protection (RDP). The pages of the Flash memory can also be protected against unwanted
write due to loss of program counter contexts. The write-protection (WRP) granularity is one
page (2 KByte). Apart of the flash memory can also be protected against read and write
from third parties (PCROP). The PCROP granularity is double word (64-bit).
3.5.1 Read protection (RDP)
The read protection is activated by setting the RDP option byte and then, by applying a
system reset to reload the new RDP option byte. The read protection protects to the Flash
main memory, the option bytes, the backup registers (RTC_BKPxR in the RTC) and the
CCM SRAM.
Note: If the read protection is set while the debugger is still connected through JTAG/SWD, apply
a POR (power-on reset) instead of a system reset.
There are three levels of read 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 Table 32.
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 Flash main memory area are possible. The
option bytes, the CCM SRAM and the backup registers are also accessible by all
operations.
Table 12. Flash memory read protection status
RDP byte value RDP complement value Read protection 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
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