XBee®/XBee‐PRO® ZB SMT RF Modules
When data is transmitted from one node to another, a network-level acknowledgement is transmitted back
across the established route to the source node. This acknowledgement packet indicates to the source node that
the data packet was received by the destination node. If a network acknowledgement is not received, the
source node will re-transmit the data.
It is possible in rare circumstances for the destination to receive a data packet, but for the source to not receive
the network acknowledgment. In this case, the source will retransmit the data, which could cause the
destination to receive the same data packet multiple times. The XBee modules do not filter out duplicate
packets. The application should include provisions to address this potential issue
See Data Transmission and Routing in chapter 4 for more information.
Receive Mode
If a valid RF packet is received, the data is transferred to the serial transmit buffer.
Command Mode
To modify or read RF Module parameters, the module must first enter into Command Mode - a state in which
incoming serial characters are interpreted as commands. Command Mode is only available over the UART when
not using the Smart Energy firmware. The API Mode section in Chapter 9 describes an alternate means for
configuring modules which is available with the SPI and with Smart Energy, as well as over the UART with ZB
code.
AT Command Mode
To Enter AT Command Mode:
Send the 3-character command sequence “+++” and observe guard times before and after the com-
mand characters. [Refer to the “Default AT Command Mode Sequence” below.]
Default AT Command Mode Sequence (for transition to Command Mode):
•No characters sent for one second [GT (Guard Times) parameter = 0x3E8]
•Input three plus characters (“+++”) within one second [CC (Command Sequence Character) parame-
ter = 0x2B.]
•No characters sent for one second [GT (Guard Times) parameter = 0x3E8]
Once the AT command mode sequence has been issued, the module sends an "OK\r" out the UART pad. The
"OK\r" characters can be delayed if the module has not finished transmitting received serial data.
When command mode has been entered, the command mode timer is started (CT command), and the
module is able to receive AT commands on the UART port.
All of the parameter values in the sequence can be modified to reflect user preferences.
NOTE: Failure to enter AT Command Mode is most commonly due to baud rate mismatch. By default,
the BD (Baud Rate) parameter = 3 (9600 bps).
To Send AT Commands:
Send AT commands and parameters using the syntax shown below.
Syntax for sending AT Commands
Carriage
Return
“AT”
ASCII
Space
Parameter
Prefix Command (optional) (optional, HEX)
Example: ATDL 1F<CR>
To read a parameter value stored in the RF module’s register, omit the parameter field.
The preceding example would change the RF module Destination Address (Low) to “0x1F”. To store the new
value to non-volatile (long term) memory, subsequently send the WR (Write) command.
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