STM8S001J3M3 datasheet(13/84 Pages) STMICROELECTRONICS

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STM8S001J3

Functional overview

There are two levels of write protection. The first level is known as MASS (memory access

security system). MASS is always enabled and protects the main Flash program memory,

data EEPROM and option bytes.

To perform in-application programming (IAP), this write protection can be removed by

writing a MASS key sequence in a control register. This allows the application to modify the

content of main program memory and data EEPROM, or to reprogram the device option

bytes.

A second level of write protection, can be enabled to further protect a specific area of

memory known as UBC (user boot code). Refer to Figure 2.

The size of the UBC is programmable through the UBC option byte (Table 12), in increments

of 1 page (64-byte block) by programming the UBC option byte in ICP mode.

This divides the program memory into two areas:

•

Main program memory: 8 Kbyte minus UBC

•

User-specific boot code (UBC): Configurable up to 8 Kbyte

The UBC area remains write-protected during in-application programming. This means that

the MASS keys do not unlock the UBC area. It protects the memory used to store the boot

program, specific code libraries, reset and interrupt vectors, the reset routine and usually

the IAP and communication routines.

Figure 2. Flash memory organization

Read-out protection (ROP)

The read-out protection blocks reading and writing the Flash program memory and data

EEPROM memory in ICP mode (and debug mode). Once the read-out protection is

activated, any attempt to toggle its status triggers a global erase of the program memory.

Even if no protection can be considered as totally unbreakable, the feature provides a very

high level of protection for a general purpose microcontroller.

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