AT commands
Networking and security commands
When MM = 1 or 3, MAC retries are not supported.
When the Digi header is disabled, encrypted data that is not valid will be sent out of the UART and not
filtered out.
Parameter range
0 - 3
Parameter
Configuration
0
1
2
3
Digi Mode (802.15.4 + Digi header)
802.15.4 (no ACKs)
802.15.4 (with ACKs)
Digi Mode (no ACKs)
Default
0
RR (XBee Retries)
This command applies to the XBee/XBee-PRO S2C 802.15.4 RF Module.
Set or reads the maximum number of retries the device executes in addition to the three retries
provided by the 802.15.4 MAC. For each device retry, the 802.15.4 MAC can execute up to three retries.
The following applies for broadcast messages: If RR = 0, only one packet is broadcast. If RR is > 0, RR
+ 2 packets are sent on each broadcast. No acknowledgments are returned on a broadcast.
This value does not need to be set on all devices for retries to work. If retries are enabled, the
transmitting device sets a bit in the Digi RF Packet header that requests the receiving device to send
an ACK. If the transmitting device does not receive an ACK within 200 ms, it re-sends the packet within
a random period up to 48 ms. Each device retry can potentially result in the MAC sending the packet
four times (one try plus three retries). Retries are not attempted for indirect messages that are purged.
Parameter range
0 - 6
Default
0
RN (Random Delay Slots)
This command applies to the XBee/XBee-PRO S2C 802.15.4 RF Module.
Sets or displays the minimum value of the back-off exponent in the CSMA-CA algorithm. The Carrier
Sense Multiple Access - Collision Avoidance (CSMA-CA) algorithm was engineered for collision
avoidance(random delays are inserted to prevent data loss caused by data collisions.
If RN = 0, there is no delay between a request to transmit and the first iteration of CSMA-CA.
Unlike CSMA-CD, which reacts to network transmissions after collisions have been detected, CSMA-CA
acts to prevent data collisions before they occur. As soon as a device receives a packet that is to be
transmitted, it checks if the channel is clear (no other device is transmitting). If the channel is clear,
the packet is sent over-the-air. If the channel is not clear, the device waits for a randomly selected
XBee/XBee-PRO S2C 802.15.4 RF Module User Guide
72
ETC [ ETC ]
