XBee‐PRO®900HP/XBee‐PRO®XSCRFModules
©2014DigiInternationalInc. 38
4.XBee‐PRO900HPSleepMode
A number of low-power modes exist to enable modules to operate for extended periods of time on battery power.
These sleep modes are enabled with the SM command. The sleep modes are characterized as either asynchronous
(SM = 1, 4, 5) or synchronous (SM = 7,8). Asynchronous sleeping modes should not be used in a synchronous
sleeping network, and vice versa.
Asynchronous sleep modes can be used to control the sleep state on a module by module basis. Modules operating
in an asynchronous sleep mode should not be used to route data. Digi strongly encourages users to set asynchro-
nous sleeping modules as non-routing nodes using the CE command. This will prevent the node from attempting to
route data.
The synchronous sleep feature of DigiMesh makes it possible for all nodes in the network to synchronize their sleep
and wake times. All synchronized cyclic sleep nodes enter and exit a low power state at the same time. This forms a
cyclic sleeping network. Nodes synchronize by receiving a special RF packet called a sync message which is sent by
a node acting as a sleep coordinator. A node in the network can become a coordinator through a process called nom-
ination. The sleep coordinator will send one sync message at the beginning of each wake period. The sync message
is sent as a broadcast and repeated by every node in the network. The sleep and wake times for the entire network
can be changed by locally changing the settings on an individual node. The network will use the most recently set
sleep settings.
Sleep Modes
Normal Mode (SM=0)
Normal mode is the default for a newly powered-on node. In this mode, a node will not sleep. Normal mode
nodes should be mains-powered.
A normal mode module will synchronize to a sleeping network, but will not observe synchronization data
routing rules (it will route data at any time, regardless of the wake state of the network). When synchronized,
a normal node will relay sync messages generated by sleep-compatible nodes but will not generate sync
messages. Once a normal node has synchronized with a sleeping network, it can be put into a sleep-
compatible sleep mode at any time.
Asynchronous Pin Sleep Mode (SM=1)
Pin sleep allows the module to sleep and wake according to the state of the Sleep_RQ pin (pin 9). Pin sleep
mode is enabled by setting the SM command to 1. When Sleep_RQ is asserted (high), the module will finish
any transmit or receive operations and enter a low-power state. The module will wake from pin sleep when the
Sleep_RQ pin is de-asserted (low). When indirect messaging polling is enabled (see the CE command), a poll
will be sent upon waking to the module's parent node as described in the Indirect Messaging and Polling
Section.
Asynchronous Cyclic Sleep Mode (SM=4)
Cyclic sleep allows the module to sleep for a specified time and wake for a short time to poll. Cyclic sleep
mode is enabled by setting the SM command to 4. In cyclic sleep, the module sleeps for a specified time. If
the XBee receives serial or RF data while awake, it will then extend the time before it returns to sleep by the
amount specified by the ST command. Otherwise, it will enter sleep mode immediately. The On_SLEEP
line is
asserted (high) when the module wakes, and is de-asserted (low) when the module sleeps. If hardware flow
control is enabled (D7 command), the CTS pin will assert (low) when the module wakes and can receive serial
data, and de-assert (high) when the module sleeps. When indirect messaging polling is enabled (see the CE
command), a poll will be sent upon waking to the module's parent node as described in the Indirect Messaging
and Polling Section.
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