Sleep modes Sleep coordinator sleep modes in the DigiMesh network
XBee® SX 868 RF Module User Guide
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sent.
2. Otherwise, the node with the preferred sleep coordinator bit set takes precedence.
3. Otherwise, a sleep support node—SM 7—takes priority over a node that is not a sleep support
node—SM 8.
4. Otherwise, the node with highest serial number becomes the sleep coordinator.
Commissioning Pushbutton option
If you enable the Commissioning Pushbutton functionality, you can immediately select a device as a
sleep coordinator by pressing the Commissioning Pushbutton twice or by issuing the CB2 command.
The device you select in this manner is still subject to the resolution criteria process.
Only potential sleep coordinator nodes honor Commissioning Pushbutton nomination requests. A
node configured as a non-sleep coordinator ignores commissioning button nomination requests.
Overriding syncs
Any sleep compatible node in the network that does not have the non-coordinator sleep option set
can send an overriding sync and become the network sleep coordinator. An overriding sync effectively
changes the synchronization of all nodes in the network to the ST and SP values of the node sending
the overriding sync. It also selects the node sending the overriding sync as the network sleep
coordinator. While this is a powerful operation, it may be an undesired side effect because the current
sleep coordinator may have been carefully selected and it is not desired to change it. Additionally the
current wake and sleep cycles may be desired rather than the parameters on the node sending the
overriding sync. For this reason, it is important to know what kicks off an overriding sync.
An overriding sync occurs whenever ST or SP is changed to a value different than OW or OS
respectively. For example no overriding sync will occur if SP is changed from 190 to C8 if the network
was already operating with OS at C8. On the other hand, if SP is changed from 190 to 190—meaning
no change—and OS is C8, than an overriding sync will occur because the network parameters are
being changed.
Even parameters that seem unrelated to sleep can kick off an overriding sync. These are NH, NN, RN,
and MT. When any of these parameters are changed, they can affect network traversal time. If such
changes cause the configured value of ST to be smaller than the value needed for network traversal,
then ST is increased and if that increased value is different than OW, then an overriding sync will
occur.
For most applications, we recommend configuring the NH, NN, RN, and MT network parameters
during initial deployment only. The default values of NH and NN are optimized to work for most
deployments. Additionally, it would be best to set ST and SP the same on all nodes in the network
while keeping ST sufficiently large so that it will not be affected by an inadvertent change of NH, NN,
RN, or MT.
Sleep guard times
To compensate for variations in the timekeeping hardware of the various devices in a sleeping router
network, the network allocates sleep guard times at the beginning and end of the wake period. The
size of the sleep guard time varies based on the sleep and wake times you select and the number of
sleep cycles that elapse since receiving the last sync message. The sleep guard time guarantees that a
destination module will be awake when the source device sends a transmission. As a node misses
more and more consecutive sync messages, the sleep guard time increases in duration and decreases
the available transmission time.
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