Sleep modes
Wake timer
XBee 868LP RF Modules User Guide
86
A newly-powered, unsynchronized, sleeping device polls for a synchronized message and then sleeps
for the period that the
SP
command specifies, repeating this cycle until it synchronizes by receiving a
sync message. Once it receives a sync message, the device synchronizes itself with the network.
Note
Configure all nodes in a synchronous sleep network to operate in either synchronous sleep
support mode or synchronous cyclic sleep mode. asynchronous sleeping nodes are not compatible
with synchronous sleeping nodes.
Wake timer
In asynchronous cyclic sleep mode (
SM
=
4
or
SM
=
5
), if a device receives serial or RF data, it starts a
sleep timer (time until sleep). Any data received serially or by RF link resets the timer. Use
to set the timer duration. While the device is awake, it sends regular poll requests to its parent
to check for buffered data. If the RF data rate is 80 kb/s (
BR
=
1
), the poll occurs every 100 ms.
Otherwise, (
BR
=
0
), the poll occurs every 300 ms. The device returns to sleep when the sleep timer
expires.
Indirect messaging and polling
To enable reliable communication with sleeping devices, you can use the
CE
(Routing/Messaging
Mode) command to enable indirect messaging and polling.
Indirect messaging
Indirect messaging is a communication mode designed for communicating with asynchronous
sleeping devices. A device can enable indirect messaging by making itself an indirect messaging
coordinator with the
CE
command. An indirect messaging coordinator does not immediately transmit
a P2MP unicast when it is received over the serial port. Instead the device holds onto the data until it
is requested via a poll. On receiving a poll, the indirect messaging coordinator sends a queued data
packet (if available) to the requestor.
Because it is possible for a polling device to be eliminated, a mechanism is in place to purge
unrequested data packets. If the coordinator holds an indirect data packet for an indirect messaging
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 end device with the
CE
command. When
you enable polling, the device sends a poll request a minimum of once every 100 ms. When the device
