SN250 datasheet(23/130 Pages) STMICROELECTRONICS

23 / 130 page

SN250

Functional description—system modules

23/130

The XAP2b clock speed is 12MHz. When used with the ZNet stack, code is loaded into

Flash memory over the air or by a serial link using a built-in bootloader in a reserved area of

the Flash. Alternatively, code may be loaded via the SIF interface with the assistance of

RAM-based utility routines also loaded via SIF.

The XAP2b in the SN250 has also been enhanced to support two separate protection

levels. The ZNet stack runs in System Mode, which allows full, unrestricted access to all

areas of the chip, while application code runs in Application Mode. When running in

Application Mode, writing to certain areas of memory and registers is restricted to prevent

common software bugs from interfering with the operation of the ZNet stack. These errant

writes are captured and details are reported to the developer to assist in tracking down and

fixing these issues.

6.6

Embedded memory

As shown in Figure 3, the program side of the address space contains mappings to both

integrated Flash and RAM blocks.

Figure 3.

Program address space

The data side of the address space contains mappings to the same Flash and RAM blocks,

as well as registers and a separate Flash information area, as shown in Figure 4.

SN250 데이터시트(PDF) 23 Page - STMicroelectronics