STM32L431XX Datasheet, PDF (17/200 Pages) STMicroelectronics – RTC with HW calendar, alarms and calibration

STM32L431xx
Functional overview
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.
Table 3. Access status versus readout protection level and execution modes
Area
Protection
level
User execution
Read
Write
Erase
Debug, boot from RAM or boot
from system memory (loader)
Read
Write
Erase
Main
1
memory
2
System
1
memory
2
Option
1
bytes
2
Backup
1
registers
2
1
SRAM2
2
Yes
Yes
Yes
No
No
No
Yes
Yes
Yes
N/A
N/A
N/A
Yes
No
No
Yes
No
No
Yes
No
No
N/A
N/A
N/A
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
N/A
N/A
N/A
Yes
Yes
N/A⁽¹⁾
No
No
N/A⁽¹⁾
Yes
Yes
N/A
N/A
N/A
N/A
Yes
Yes
Yes⁽¹⁾
No
No
No⁽¹⁾
Yes
Yes
Yes
N/A
N/A
N/A
1. Erased when RDP change from Level 1 to Level 0.
• 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.
DocID028800 Rev 1
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