Datasheet

DocID028800 Rev 1 17/200
STM32L431xx Functional overview
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3.4 Embedded Flash memory
STM32L431xx devices feature up to 256 Kbyte of embedded Flash memory available for
storing programs and data in single bank architecture. The Flash memory contains 128
pages of 2 Kbyte.
Flexible protections can be configured thanks to option bytes:
• Readout protection (RDP) to protect the whole memory. Three levels are available:
– Level 0: no readout protection
– Level 1: memory readout protection: the Flash memory cannot be read from or
written to if either debug features are connected, boot in RAM or bootloader is
selected
– Level 2: chip readout protection: debug features (Cortex-M4 JTAG and serial
wire), boot in RAM and bootloader selection are disabled (JTAG fuse). This
selection is irreversible.
• Write protection (WRP): the protected area is protected against erasing and
programming. Two areas can be selected, with 2-Kbyte granularity.
• Proprietary code readout protection (PCROP): a part of the flash memory can be
protected against read and write from third parties. The protected area is execute-only:
it can only be reached by the STM32 CPU, as an instruction code, while all other
accesses (DMA, debug and CPU data read, write and erase) are strictly prohibited.
The PCROP area granularity is 64-bit wide. An additional option bit (PCROP_RDP)
allows to select if the PCROP area is erased or not when the RDP protection is
changed from Level 1 to Level 0.
Table 3. Access status versus readout protection level and execution modes
Area
Protection
level
User execution
Debug, boot from RAM or boot
from system memory (loader)
Read Write Erase Read Write Erase
Main
memory
1 Yes Yes Yes No No No
2 Yes Yes Yes N/A N/A N/A
System
memory
1 Yes No No Yes No No
2 Yes No No N/A N/A N/A
Option
bytes
1 Yes Yes Yes Yes Yes Yes
2 Yes No No N/A N/A N/A
Backup
registers
1YesYesN/A
(1)
1. Erased when RDP change from Level 1 to Level 0.
No No N/A
(1)
2 Yes Yes N/A N/A N/A N/A
SRAM2
1 Yes Yes Yes
(1)
No No No
(1)
2 Yes Yes Yes N/A N/A N/A
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