User's Manual

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WSM2400 includes a soft brown-out monitor that fully protects the flash from corruption in the event
that power is removed while writing to flash. Integrated flash supervisory functionality, in conjunction
with a fault tolerant file system, yields a robust non-volatile storage solution.
PRECISION TIMING
A major feature of WSM2400 over competing 802.15.4 product offerings is its low-power dedicated
timing hardware and timing algorithms. This functionality provides timing precision two to three orders
of magnitude better than any other low-power solution available at the time of publication. Improved
timing accuracy allows motes to minimize the amount of radio listening time required to ensure packet
reception thereby lowering even further the power consumed by SmartMesh networks. WSM2400’s
patented timing hardware and timing algorithms provide superior performance over rapid temperature
changes, further differentiating WSM2400’s reliability when compared with other wireless products. In
addition, precise timing enables networks to reduce spectral dead time, increasing total network
throughput.
APPLICATION TIME SYNCHRONIZATION
In addition to coordinating time slots across the network, which is transparent to the user, WSM2400’s
timing management is used to support two mechanisms to share network time. Having an accurate,
shared, network-wide time base enables events to be accurately time stamped or tasks to be performed
in a synchronized fashion across a network. WSM2400 will send a time packet through its serial
interface when one of the following occurs:
 WSM2400 receives an API request to read time
 The TIMEn signal is asserted
The use of TIMEn has the advantage of being more accurate. The value of the timestamp is captured in
hardware relative to the rising edge of TIMEn. If an API request is used, due to packet processing, the
value of the timestamp may be captured several milliseconds after receipt of the packet due to packet
processing. See the TIMEn AC Characteristics section for the time function’s definition and
specifications.
TIME REFERENCES
WSM2400 includes three clock sources: an internal relaxation oscillator, a low power oscillator designed
for a 32.768kHz crystal, and the radio reference oscillator designed for a 20MHz crystal.
RELAXATION OSCILLATOR
The relaxation oscillator is the primary clock source for WSM2400, providing the clock for the CPU,
memory subsystems, and all peripherals. The internal relaxation oscillator is dynamically calibrated to
7.3728 MHz. The internal relaxation oscillator typically starts up in a few μs, providing an expedient, low