User Manual

XBee®/XBee‐PRO®RFModules‐802.15.4‐v1.xEx[2011.06.1]
©2011DigiInternatonal,Inc. 19
Association
Association is the establishment of membership between End Devices and a Coordinator. The
establishment of membership is useful in scenarios that require a central unit (Coordinator) to
relay messages to or gather data from several remote units (End Devices), assign channels or
assign PAN IDs.
An RF data network that consists of one Coordinator and one or more End Devices forms a PAN
(Personal Area Network). Each device in a PAN has a PAN Identifier [ID (PAN ID) parameter]. PAN
IDs must be unique to prevent miscommunication between PANs. The Coordinator PAN ID is set
using the ID (PAN ID) and A2 (Coordinator Association) commands.
An End Device can associate to a Coordinator without knowing the address, PAN ID or channel of
the Coordinator. The A1 (End Device Association) parameter bit fields determine the flexibility of
an End Device during association. The A1 parameter can be used for an End Device to dynamically
set its destination address, PAN ID and/or channel.
Coordinator / End Device Setup and Operation
To configure a module to operate as a Coordinator, set the CE (Coordinator Enable) parameter to
‘1’. Set the CE parameter of End Devices to ‘0’ (default). Coordinator and End Devices should con-
tain matching firmware versions.
NonBeacon (w/ Coordinator) Systems
The Coordinator can be configured to use direct or indirect transmissions. If the SP (Cyclic Sleep
Period) parameter is set to ‘0’, the Coordinator will send data immediately. Otherwise, the SP
parameter determines the length of time the Coordinator will retain the data before discarding it.
Generally, SP (Cyclic Sleep Period) and ST (Time before Sleep) parameters should be set to match
the SP and ST settings of the End Devices.
Coordinator Start-up
Coordinator power-up is governed by the A2 (Coordinator Association) command. On power-up,
the Coordinator undergoes the following sequence of events:
1. Check A2 parameter- Reassign_PANID Flag
Set (bit 0 = 1) - The Coordinator issues an Active Scan. The Active Scan selects one channel
and transmits a request to the broadcast address (0xFFFF) and broadcast PAN ID (0xFFFF). It
then listens on that channel for beacons from any Coordinator operating on that channel. The
listen time on each channel is determined by the SD (Scan Duration) parameter value.
Once the time expires on that channel, the Active Scan selects another channel and again
transmits the BeaconRequest as before. This process continues until all channels have been
scanned, or until 5 PANs have been discovered. When the Active Scan is complete, the results
include a list of PAN IDs and Channels that are being used by other PANs. This list is used to
assign an unique PAN ID to the new Coordinator. The ID parameter will be retained if it is not
found in the Active Scan results. Otherwise, the ID (PAN ID) parameter setting will be updated
to a PAN ID that was not detected.
Not Set (bit 0 = 0) - The Coordinator retains its ID setting. No Active Scan is performed.
For example: If the PAN ID of a Coordinator is known, but the operating channel is not; the A1
command on the End Device should be set to enable the ‘Auto_Associate’ and
‘Reassign_Channel’ bits. Additionally, the ID parameter should be set to match the PAN ID of
the associated Coordinator.