Sleep modes Sleeping routers
XBee®-PRO 900HP/XSC RF Modules
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poller for more than 2.5 times its SP value, then the packet is purged. We suggest setting the SP of
the coordinator to the same value as the highest SP time that exists among the pollers in the
network. If the coordinator is in API mode, a TxStatus message is generated for a purged data packet
with a status of 0x75 (INDIRECT_MESSAGE_UNREQUESTED).
An indirect messaging coordinator queues up as many data packets as it has buffers available. After
the coordinator uses all of its available buffers, it holds transmission requests unprocessed on the
serial input queue. After the serial input queue is full, the device de-asserts CTS (if hardware flow
control is enabled). After receiving a poll or purging data from the indirect messaging queue the
buffers become available again.
Indirect messaging only functions with P2MP unicast messages. Indirect messaging has no effect on
P2MP broadcasts, directed broadcasts, repeater packets, or DigiMesh packets. These messages are
sent immediately when received over the serial port and are not put on the indirect messaging queue.
Polling
Polling is the automatic process by which a node can request data from an indirect messaging
coordinator. To enable polling on a device, configure it as an indirect messaging poller with the CE
command and set its DH:DL registers to match the SH:SL registers of the device that will function as
the Indirect Messaging Coordinator. When you enable polling, the device sends a P2MP poll request
regularly to the address specified by the DH:DL registers. When the device sends a P2MP unicast to
the destination specified by the DH:DL of a polling device, the data also functions as a poll.
When a polling device is also an asynchronous sleeping device, that device sends a poll shortly after
waking from sleep. After that first poll is sent, the device sends polls in the normal manner described
previously until it returns to sleep.
The 200 K data rate firmware sends polls at least every 100 ms when awake. The 10 K data rate
firmware sends polls at least every 300 ms when awake.
Sleeping routers
The Sleeping Router 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. For more information, see Become a sleep
coordinator.
Sleep coordinator sleep modes in the DigiMesh network
In a synchronized sleeping network, one node acts as the sleep coordinator. During normal
operations, at the beginning of a wake cycle the sleep coordinator sends a sync message as a
broadcast to all nodes in the network. This message contains synchronization information and the
wake and sleep times for the current cycle. All cyclic sleep nodes that receive a sync message remain
awake for the wake time and then sleep for the specified sleep period.
The sleep coordinator sends one sync message at the beginning of each cycle with the current wake
and sleep times. All router nodes that receive this sync message relay the message to the rest of the
network. If the sleep coordinator does not hear a rebroadcast of the sync message by one of its
immediate neighbors, then it re-sends the message one additional time.
If you change the SP or ST parameters, the network does not apply the new settings until the
beginning of the next wake time. For more information, see Change sleep parameters.
A sleeping router network is robust enough that an individual node can go several cycles without
receiving a sync message, due to RF interference, for example. As a node misses sync messages, the
time available for transmitting messages during the wake time reduces to maintain synchronization
accuracy. By default, a device reduces its active sleep time progressively as it misses sync messages.
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