Digi XBee Product Manual

API Operation for the XBee/XBee-PRO RF Module
XBee / XBee-PRO RF Modules 802.15.4 Product Manual 89
<(Special)> The WR command is used to write configurable parameters to the RF module's non-
volatile memory. Parameter values remain in the module's memory until overwritten by subsequent
use of the WR Command.
If changes are made without writing them to non-volatile memory, the module reverts back to
previously saved parameters the next time the module is powered-on.
Note Once the WR command is sent to the module, no additional characters should be sent until
after the “OK/r” response is received.
API Operation for the XBee/XBee-PRO RF Module
By default, XBee / XBee-PRO RF Modules act as a serial line replacement (Transparent Operation) - all
UART data received through the DI pin is queued up for RF transmission. When the module receives
an RF packet, the data is sent out the DO pin with no additional information.
Inherent to Transparent Operation are the following behaviors:
• If module parameter registers are to be set or queried, a special operation is required for
transitioning the module into Command Mode.
• In point-to-multipoint systems, the application must send extra information so that the receiving
module(s) can distinguish between data coming from different remotes.
As an alternative to the default Transparent Operation, Application Programming Interface (API)
operations are available. API operation requires that communication with the module be done
through a structured interface (data is communicated in frames in a defined order). The API specifies
how commands, command responses and module status messages are sent and received from the
module using a UART data frame.
API frame specifications
Two API modes are supported and both can be enabled using the AP (API Enable) command. Use the
following AP parameter values to configure the module to operate in a particular mode:
• AP = 0 (default): Transparent Operation (UART Serial line replacement)
API modes are disabled.
• AP = 1: API Operation
• AP = 2: API Operation (with escaped characters)
Any data received prior to the start delimiter is silently discarded. If the frame is not received
correctly or if the checksum fails, the data is silently discarded.
API Operation (AP parameter = 1)
When this API mode is enabled (AP = 1), the UART data frame structure is defined as follows:
Figure 12: UART data frame structure:
MSB = Most Significant byte, LSB = Least Significant byte
Start Delimiter
(Byte 1)
Length
(Bytes 2-3)
Frame Data
(Bytes 4-n)
Checksum
(Byte n + 1)
0x7E MSB LSB API-specific Structure 1 Byte

Digi XBee Specifications

General

Operating Frequency	2.4 GHz
RF Data Rate	250 kbps
Model	XBee S2C
Category	Control Unit
Operating Voltage	2.1 to 3.6V DC
Operating Temperature	-40 to +85 °C
Interface	UART
Dimensions	24.38 x 27.61 x 9.14 mm