PM0054

Memory protection strategy

Doc ID 15433 Rev 9

13/28

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Memory protection strategy

The STM8 devices feature several mechanisms allowing to protect the content of the Flash

program and data EEPROM areas:

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Readout protection

The software can prevent application code, data stored in the Flash program memory

and data EEPROM from being read and modified in ICP/SWIM mode.

Readout protection is enabled and disabled by an option byte in ICP/SWIM mode.

Refer to Section 4.1 for details.

●

Proprietary code area (PCODE) protection

To protect proprietary peripheral software driver libraries, some STM8 devices feature a

permanently readout-protected area, the proprietary code area (PCODE).

This area is in Flash program memory. Its content cannot be modified and can only be

read/executed in user privileged mode.

The PCODE area size can be configured in ICP/SWIM mode through an option byte in

increments of one page.

The PCODE area is not available on all devices.

Refer to Table 11: Comparison of STM8L devices for the devices featuring PCODE

area, and to Section 4.2 for details on PCODE area.

●

User boot code area (UBC) protection

To guarantee recovery capability from an interrupted or erroneous IAP program, STM8

devices provide a write-protected area called user boot code (UBC).

This area is in Flash program memory and cannot be modified in user mode (it is

protected against modification by user software).

The UBC area content can be modified only in ICP/SWIM mode after clearing the UBC

option byte.

The UBC area size can be configured through an option byte in increments of one

page.

Refer to Section 4.3 for details on user boot code area.

●

Unwanted memory access protection

All STM8 devices offer unwanted memory access protection, to prevent unintentional

modification of program memory or data EEPROM (for example due to a firmware bug

or EMC disturbance).

This protection consists of authorizing write access to the memory only through a

specific software sequence which is unlikely to happen randomly or by mistake.

Access to Flash program and data EEPROM areas is enabled by writing MASS keys

into key registers.

Refer to Section 4.4 for details on unwanted memory access protection.