XBee‐PRO®900HP/XBee‐PRO®XSCRFModules
©2014DigiInternationalInc. 77
Link Testing
A good way to measure the performance of a network is to send unicast data through the network from one
device to another to determine the success rate of many transmissions. To simplify link testing, the modules
support a loopback cluster ID (0x12) on the data endpoint (0xE8). Any data sent to this cluster ID on the data
endpoint will be transmitted back to the sender.
The configuration steps to send data to the loopback cluster ID depend on the AP setting:
AT Configuration (AP=0)
To send data to the loopback cluster ID on the data endpoint of a remote device, set the CI command value to
0x12. The SE and DE commands should be set to 0xE8 (default value). The DH and DL commands should be
set to the address of the remote (0 for the coordinator, or the 64-bit address of the remote). After exiting
command mode, any received serial characters will be transmitted to the remote device, and returned to the
sender.
API Configuration (AP=1 or AP=2)
Send an Explicit Addressing Command API frame (0x11) using 0x12 as the cluster ID and 0xE8 as the source
and destination endpoint. Data packets received by the remote will be echoed back to the sender.
RSSI Indicators
It is possible to measure the received signal strength on a device using the DB command. DB returns the RSSI
value (measured in -dBm) of the last received packet. However, this number can be misleading in DigiMesh
networks. The DB value only indicates the received signal strength of the last hop. If a transmission spans
multiple hops, the DB value provides no indication of the overall transmission path, or the quality of the worst
link - it only indicates the quality of the last link and should be used accordingly.
The DB value can be determined in hardware using the RSSI/PWM module pin (pin 6). If the RSSI PWM
functionality is enabled (P0 command), when the module receives data, the RSSI PWM is set to a value based
on the RSSI of the received packet. (Again, this value only indicates the quality of the last hop.) This pin could
potentially be connected to an LED to indicate if the link is stable or not.
XBee-PRO 900HP Device Discovery
Network Discovery
The network discovery command can be used to discover all Digi modules that have joined a network. Issuing
the ND command sends a broadcast network discovery command throughout the network. All devices that
receive the command will send a response that includes the device’s addressing information, node identifier
string (see NI command), and other relevant information. This command is useful for generating a list of all
module addresses in a network.
When a device receives the network discovery command, it waits a random time before sending its own
response. The maximum time delay is set on the ND sender with the NT command. The ND originator includes
its NT setting in the transmission to provide a delay window for all devices in the network. Large networks
may need to increase NT to improve network discovery reliability. The default NT value is 0x82 (13 seconds).
Neighbor Polling
The neighbor poll command can be used to discover the modules which are immediate neighbors (within RF
range) of a particular node. This command is useful in determining network topology and determining possible
routes. The command is issued using the FN command. The FN command can be initiated locally on a node
using AT command mode or by using a local AT command request frame. The command can also be initiated
remotely by sending the target node an FN command using a remote AT command request API frame.
A node which executes an FN command will send a broadcast to all of its immediate neighbors. All radios
which receive this broadcast will send an RF packet to the node that initiated the FN command. In the case
where the command is initiated remotely this means that the responses are sent directly to the node which
sent the FN command to the target node. The response packet is output on the initiating radio in the same
format as a network discovery frame.
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