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Manage End Devices I/O sampling
XBee/XBee-PRO® S2C ZigBee® RF Module 138
This firmware includes an adaptive polling enhancement where, if an end device receives RF data from
its parent, it sends another poll after a very short delay to check for more data. The end device
continues to poll at a faster rate as long as it receives data from its parent. This feature greatly
improves data throughput to end devices. When the end device no longer receives data from its
parent, it resumes polling every 100 ms.
I/O sampling
End devices can be configured to send one or more I/O samples when they wake from sleep. To
enable I/O sampling on an end device, the IR command must be set to a non-zero value, and at least
one analog or digital I/ O pin must be enabled for sampling (
D0 - D9 , P0 - P4 commands). If I/O
sampling is enabled, an end device sends an I/O sample when it wakes and starts the ST timer. It will
continue sampling at the IR rate until the sleep timer ( ST ) has expired. For more information, see
Analog and digital I/O lines .
Waking end devices with the Commissioning Pushbutton
If you use D0 (AD0/DIO0 Configuration) to enable the Commissioning Pushbutton functionality, a high-
to-low transition on the AD0/ DIO0 pin (pin 33) causes an end device to wake for 30 seconds. For more
information, see
Commissioning pushbutton and associate LED .
Parent verification
Since an end device relies on its parent to maintain connectivity with other devices in the network,
XBee end devices include provisions to verify the connection with its parent. End devices monitor the
link with their parent when sending poll messages and after a power cycle or reset event as described
below.
When an end device wakes from sleep, it sends a poll request to its parent. In cyclic sleep, if the end
device does not receive RF or serial data and the sleep timer is not started, it polls one time and
returns to sleep for another sleep period. Otherwise, the end device continues polling every 100ms. If
the parent does not send an acknowledgment response to three consecutive poll request
transmissions, the end device assumes the parent is out of range, and attempts to find a new parent.
After a power-up or reset event, the end device does an orphan scan to locate its parent. If the parent
does not send a response to the orphan scan, the end device attempts to find a new parent.
Rejoining
Once all devices have joined a ZigBee network, disable the permit-joining attribute disabled such that
new devices are no longer allowed to join the network. You can enable permit-joining later as needed
for short times. This provides some protection in preventing other devices from joining a live network.
If an end device cannot communicate with its parent, the end device must be able to join a new parent
to maintain network connectivity. However, if permit-joining is disabled in the network, the end device
will not find a device that is allowing new joins.
To overcome this problem, ZigBee supports rejoining, where an end device can obtain a new parent in
the same network even if joining is not enabled. When an end device joins using rejoining, it performs a
PAN ID scan to discover nearby networks. If a network is discovered that has the same 64-bit PAN ID
as the end device, it joins the network by sending a rejoin request to one of the discovered devices.
The device that receives the rejoin request sends a rejoin response if it can allow the device to join the
network (that is, the child table is not full). You can use the rejoin mechanism to allow a device to join
the same network even if permit-joining is disabled.