SN250 datasheet(24/130 Pages) STMICROELECTRONICS

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Functional description—system modules

SN250

24/130

Figure 4.

Data address space

6.6.1

Flash memory

The SN250 integrates 128KB of Flash memory. The Flash cell has been qualified for a data

retention time of >100 years at room temperature. Each Flash page size is 1024 bytes and

is rated to have a guaranteed 1,000 write/erase cycles.

The Flash memory has mappings to both the program and data side address spaces. On

the program side, the first 112KB of the Flash memory are mapped to the corresponding

first 56k word addresses to allow for code storage, as shown in Figure 3.

On the program side, the Flash is always read as whole words. On the data side, the Flash

memory is divided into eight 16KB sections, which can be separately mapped into a Flash

window for the storage of constant data and the Simulated EEPROM. As shown in Figure 4,

the Flash window corresponds to the first 16KB of the data-side address space. On the data

side, the Flash may be read as bytes, but can only be written to one word at a time using

utility routines in the ZNet stack and HAL.

6.6.2

Simulated EEPROM

The ZNet stack reserves a section of Flash memory to provide Simulated EEPROM storage

area for stack and customer tokens. Therefore, the SN250 utilizes 8KB of upper Flash

storage. This section of Flash is only accessible when mapped to the Flash window in the

data-side address space. Because the Flash cells are qualified for up to 1,000 write cycles,

SN250 Datasheet(PDF) 24 Page - STMicroelectronics