Memory protection strategy

PM0212

8/22

Doc ID 022351 Rev 2

3

Memory protection strategy

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

program and data EEPROM areas:

●

Readout protection

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

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

readout protection is enabled and disabled by programming an option byte in

ICP/SWIM mode. Refer to Section 3.1: Readout protection for details.

●

Proprietary code area (PCODE)

To protect proprietary peripheral software driver libraries, some STM8 devices features

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

is part of the Flash program memory. Its content cannot be modified and can only be

read/executed in user privileged mode.

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

byte by increments of one page.

Refer to Section 3.2 for details on PCODE area.

●

User boot code area (UBC)

In order to guaranty the capability to recover from an interrupted or erroneous IAP

programming, all STM8 devices provide a write-protected area called user boot code

(UBC). This area is a part of the Flash program memory which cannot be modified in

user mode (that is protected against modification by the user software). The content of

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

byte.

The size of the user boot code area can be configured through an option byte by

increments of one page.

Refer to Section 3.3: User Boot Code area protection for details on user boot code

area.

●

Unwanted memory access protection

All STM8 devices offer unwanted memory access protection, which purpose is to

prevent unintentional modification of program memory and 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 3.4: Unwanted memory access protection for details on unwanted

memory access protection.