Module operation Modes of operation
XBee/XBee-PRO ZigBee RF Modules User Guide 31
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 on page 54 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. Refer to Supporting the API on page 114 for an
alternate means of configuring modules.
AT Command Mode
Entering AT Command Mode
Send the three-character command sequence +++ and observe guard times before and after the command
characters. Refer to the “Default AT Command Mode Sequence.”
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) parameter = 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 DOUT pin. 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 DIN pin.
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 b/s).
Sending AT commands
Send AT commands and parameters using the syntax shown below.
Figure 1: Syntax for sending AT commands
Note 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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