STM8S001J3 datasheet(13/84 Pages) STMICROELECTRONICS

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DS12129 Rev 4

13/84

STM8S001J3

Functional overview

Write protection (WP)

Write protection of Flash program memory and data EEPROM is provided to avoid

unintentional overwriting of memory that could result from a user software malfunction.

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

MS36408V1

Low density

Flash program

memory

(8 Kbytes)

Programmable

area from 64 bytes

(1 page) up to

8 Kbytes

(in 1 page steps)

Program memory area

Write access possible for IAP

UBC area

Remains write protected during IAP

Data EEPROM (128 bytes)

Option bytes

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