SN260 datasheet(18/88 Pages) STMICROELECTRONICS

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Functional description

SN260

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5.6.1

Simulated EEPROM

The protocol stack reserves a section of Flash memory to provide simulated EEPROM

storage area for stack and customer tokens. The Flash cell has been qualified for a data

retention time of >100 years at room temperature and is rated to have a guaranteed 1,000

write/erase cycles. Because the Flash cells are qualified for up to 1,000 write cycles, the

simulated EEPROM implements an effective wear-leveling algorithm which effectively

extends the number of write cycles for individual tokens.

The number of set-token operations is finite due to the write cycle limitation of the Flash. It is

not possible to guarantee an exact number of set-token operations because the life of the

simulated EEPROM depends on which tokens are written and how often.

The SN260 stores non-volatile information necessary for network operation as well as 8

tokens available to the Host (see section Section 7.2.6: Tokens on page 37). The majority of

internal tokens are only written when the SN260 performs a network join or leave operation.

As a simple estimate of possible set-token operations, consider an SN260 in a stable

network (no joins or leaves) not sending any messages where the Host uses only one of the

8-byte tokens available to it. Under this scenario, a very rough estimate results in

approximately 330,000 possible set-token operations. The number of possible set-token

calls, though, depends on which tokens are being set, so the ratios of set-token calls for

each token plays a large factor. A very rough estimate for the total number of times an App

token can be set is approximately 320,000.

These estimates would typically increase if the SN260 is kept closer to room temperature,

since the 1,000 guaranteed write cycles of the Flash is for across temperature.

5.6.2

Flash information area (FIA)

The SN260 also includes a separate 1024-byte FIA that can be used for storage of data

during manufacturing, including serial numbers and calibration values. Programming of this

special Flash page can only be enabled using the SIF interface to prevent accidental

corruption or erasure. The EmberZNet stack reserves a small portion of this space for its

own use and in addition makes eight manufacturing tokens available to the application. See

Section 7.2.6: Tokens on page 37, for more information.

5.7

Encryption accelerator

The SN260 contains a hardware AES encryption engine that is attached to the CPU using a

memory-mapped interface. NIST-based CCM, CCM*, CBC-MAC, and CTR modes are

implemented in hardware. These modes are described in the IEEE 802.15.4-2003

specification, with the exception of CCM*, which is described in the ZigBee Security

Services Specification 1.0. The EmberZNet stack implements a security API for applications

that require security at the application level.

SN260 Datasheet(PDF) 18 Page - STMicroelectronics

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