© 2014 Digi International Inc. 46
XBee/XBee-PRO
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DigiMesh 2.4 User Manual
XBee/XBee-PRO DigiMesh 2.4 Sleep Modes
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). Do not use
Asynchronous sleeping modes in a synchronous sleeping network, and vice versa.
Asynchronous sleep modes are used to control the sleep state on a module by module basis. Do
not use modules operating in asynchronous mode to route data. Digi strongly encourages users
to set asynchronous sleeping modules as end-devices 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
nomination. 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.
DigiMesh Sleep Modes
Normal Mode (SM=0)
Normal mode is the default for a newly powered-on node. In this mode, a node does not sleep.
Normal mode nodes should be mains-powered.
A normal mode module synchronizes 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). Enable Pin sleep mode 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 wakes from pin sleep when the Sleep_RQ pin is de-asserted (low).
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