XBee‐PRO®900HP/XBee‐PRO®XSCRFModules
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XBee-PRO 900HP Indirect Messaging and Polling (P2MP Packets Only)
The messaging mode command (CE) can be used to enable indirect messaging and polling. This enables
reliable communication with asynchronous sleeping devices.
Indirect Messaging
Indirect messaging is a communication mode designed for communicating with asynchronous sleeping
devices. A module 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 module holds onto the data until it is requested via a poll. On
receiving a poll the indirect messaging coordinator will send a queued data packet (if available) to the
requestor.
Because it is possible for 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. Users are encouraged to set 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 will queue up as many data packets as it has buffers available. After the
coordinator has used all of its available buffers, it will hold transmission requests unprocessed on the serial
input queue. After the serial input queue is full, CTS
will be de-asserted (if hardware flow control is enabled).
Obviously, after receiving a poll or purging data from the indirect messaging queue the buffers become
available again.
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.
Polling can be enabled on a device by configuring it as an indirect messaging poller with the CE command and
setting its DH:DL registers to match the SH:SL registers of the module which will function as the Indirect
Messaging Coordinator. When polling is enabled, the module will send a P2MP poll request regularly to the
address specified by the DH:DL registers. When a P2MP unicast is sent to the destination specified by the
DH:DL of an a polling module, the data will also function as a poll.
When a polling device is also an asynchronous sleeping device, then that device will send a poll shortly after
waking from sleep. After that first poll is sent, the module will send polls in the normal manner described
above until it returns to sleep.
The 200K data rate product will send polls at least every 100ms when awake. The 10K data rate product will
send polls at least every 300ms when awake.
Synchronous Sleep Operation (DigiMesh networks only)
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. 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 sleep
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.
Operation
One node in a sleeping network acts as the sleeping coordinator. The process by which a node becomes a
sleep coordinator is described later in this document. During normal operations, at the beginning of a wake
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