Manage End Devices
Router/Coordinator configuration
XBee/XBee-PRO® S2C ZigBee® RF Module
139
To enable rejoining, set
NJ
to less than 0xFF on the device joining. If NJ < 0xFF, the device assumes
the network is not allowing joining and first tries to join a network using rejoining. If multiple rejoining
attempts fail, or if NJ=0xFF, the device attempts to join using association.
Router/Coordinator configuration
XBee routers and coordinators may require some configuration to ensure the following are set
correctly.
n
RF Packet buffering timeout
n
Child poll timeout
n
Transmission timeout
The value of these timeouts depends on the sleep time used by the end devices.
RF packet buffering timeout
When a router or coordinator receives an RF data packet intended for one of its end device children, it
buffers the packet until the end device wakes and polls for the data, or until a packet buffering
timeout occurs. Use the
SP
command to set the timeout . The actual timeout is (1.2 * SP), with a
minimum timeout of 1.2 seconds and a maximum of 30 seconds. Since the packet buffering timeout is
set slightly larger than the
SP
setting, set
SP
the same on routers and coordinators as it is on cyclic
sleep end devices. For pin sleep devices, set
SP
as long as the pin sleep device can sleep, up to 30
seconds.
Note
In pin sleep and extended cyclic sleep, end devices can sleep longer than 30 seconds. If end
devices sleep longer than 30 seconds, parent and non-parent devices must know when the end device
is awake in order to reliably send data. For applications that require sleeping longer than 30 seconds,
end devices should transmit an
I/O
sample or other data when they wake to alert other devices that
they can send data to the end device.
Child poll timeout
Router and coordinator devices maintain a timestamp for each end device child indicating when the
end device sent its last poll request to check for buffered data packets. If an end device does not send
a poll request to its parent for a certain period of time, the parent assumes the end device has moved
out of range and removes the end device from its child table. This allows routers and coordinators to
be responsive to changing network conditions. You can issue the
NC
command at any time to read the
number of remaining (unused) child table entries on a router or coordinator.
Set the child poll timeout with the
SP
and
SN
commands.
SP
and
SN
should be set such that
SP
*
SN
matches the longest expected sleep time of any end devices in the network. The device calculates the
actual timeout as (3*
SP
*
SN
), with a minimum of 5 seconds. For networks consisting of pin sleep end
devices, set the
SP
and
SN
values on the coordinator and routers so the
SP
*
SN
matches the longest
expected sleep period of any pin sleep device. The 3 multiplier ensures the end device will not be
removed unless 3 sleep cycles pass without receiving a poll request. You can set the poll timeout up to
two months.
Adaptive polling
The PO command determines the regular polling rate. However, if RF data has been recently received
by an end device, it is likely that more RF data could be on the way. Therefore, the end device polls at
a faster rate, gradually decreasing its adaptive poll rate until polling resumes at the regular rate as
defined by the
PO
command.