Digi XBee, Руководство пользователя, Страница: 73 / 307

ZigBee networks ZigBee channel scanning
XBee/XBee-PRO® S2C ZigBee® RF Module 73
ZigBee channel scanning
Routers and end devices must scan one or more channels to discover a valid network to join. When a
join attempt begins, the device sends a beacon request transmission on the lowest channel specified
in the
SC (Scan Channels) bitmask. If the device finds a valid PAN on the channel, it attempts to join
the PAN on that channel. Otherwise, if the device does not find a valid PAN on the channel, it attempts
scanning on the next higher channel in the
SC bitmask.
The device continues to scan each channel (from lowest to highest) in the SC bitmask until it finds a
valid PAN or all channels have been scanned. Once the device scans all channels, the next join attempt
starts scanning on the lowest channel specified in the
SC bitmask.
For example, if the SC command is set to 0x400F , the device starts scanning on channel 11 ( 0x0B ) and
scans until it finds a valid beacon, or until it scans channels 11, 12, 13, 14, and 25 have been scanned
(in that order).
Once an XBee router or end device joins a network on a given channel, if the XBee device receives a
network leave command (see
Leave a network ), it leaves the channel it joined on and continues
scanning on the next higher channel in the SC bitmask.
For example, if the SC command is set to 0x400F and the device joins a PAN on channel 12 ( 0x0C ), if
the XBee/XBee-PRO ZigBee RF Module leaves the channel, it starts scanning on channel 13, followed
by channels 14 and 25 if it does not find a valid network. Once all channels have been scanned, the
next join attempt starts scanning on the lowest channel specified in the
SC bitmask.
Manage multiple ZigBee networks
In some applications, multiple ZigBee networks may exist in proximity of each other. The application
may need provisions to ensure the device joins the desired network. There are a number of features in
ZigBee to manage joining among multiple networks. These include the following:
n
PAN ID Filtering
n
Preconfigured Security Keys
n
Permit Joining
n
Application Messaging
Filter PAN ID
Set ID (Extended PAN ID) to a non-zero value to configure the XBee/XBee-PRO ZigBee RF Module with
a fixed PAN ID.
If you set the PAN ID to a non-zero value, the device will only join a network with the same PAN ID.
Configure security keys
Similar to PAN ID filtering, this method requires that you install a known security key on a router to
ensure it joins a ZigBee network with the same security key.
1. Use EE (Encryption Enable) to enable security.
2. Use KY (Link Key) to set the security key to a non-zero value.
Now the XBee router or end device will only join a network with the same security key.
Prevent unwanted devices from joining
You can disable the permit-joining parameter in a network to prevent unwanted devices from joining.
When you need to add a new device to a network, enable permit-joining for a short time on the