STM8S207xx, STM8S208xx
Product overview
4.4
Flash program and data EEPROM memory
●
●
●
Up to 128 Kbytes of high density Flash program single voltage Flash memory
Up to 2K bytes true data EEPROM
Read while write: Writing in data memory possible while executing code in program
memory.
●
User option byte area
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 write to data
EEPROM, modify the contents of main program memory or 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 13.), in
increments of 1 page (512 bytes) by programming the UBC option byte in ICP mode.
This divides the program memory into two areas:
●
Main program memory: Up to 128 Kbytes minus UBC
●
User-specific boot code (UBC): Configurable up to 128 Kbytes
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 organisation
Data memory area (2 Kbytes)
Option bytes
Data
EEPROM
memory
Programmable area from 1 Kbyte
(2 first pages) up to 128 Kbytes
(1 page steps)
UBC area
Remains write protected during IAP
Up to
128 Kbytes
Flash
program
memory
Program memory area
Write access possible for IAP
Doc ID 14733 Rev 9
15/103
STMICROELECTRONICS [ ST ]
