© 2014 Digi International Inc. 70
XBee/XBee-PRO
®
DigiMesh 2.4 User Manual
1 MSB = Most Significant Byte, LSB = Least Significant Byte
XBee Escape Characters
When sending or receiving a UART data frame, specific data values must be escaped (flagged)
so they do not interfere with the data frame sequencing. To escape an interfering data byte,
insert 0x7D and follow it with the byte to be escaped XOR’d with 0x20.
Data bytes that need to be escaped:
• 0x7E – Frame Delimiter
• 0x7D – Escape
• 0x11 – XON
• 0x13 – XOFF
Example: Raw UART Data Frame (before escaping interfering bytes):
0x7E 0x00 0x02 0x23 0x11 0xCB
0x11 needs to be escaped which results in the following frame:
0x7E 0x00 0x02 0x23 0x7D 0x31 0xCB
Note: In the above example, the length of the raw data (excluding the checksum) is 0x0002
and the checksum of the non-escaped data (excluding frame delimiter and length) is
calculated as: 0xFF - (0x23 + 0x11) = (0xFF - 0x34) = 0xCB.
Length: The length field has two-byte value that specifies the number of bytes that will be
contained in the frame data field. It does not include the checksum field.
XBee UART Frame Data
Frame data of the UART data frame forms an API-specific structure as follows:
UART Data Frame & API-specific Structure:
The cmdID frame (API-identifier) indicates which API messages will be contained in the cmdData
frame (Identifier-specific data). Note that multi-byte values are sent big endian.The XBee
modules support the following API frames:
API Frame Names API ID
AT Command 0x08
AT Command-Queue Parameter Value 0x09
Transmit Request 0x10
Explicit Addressing Command Frame 0x11
Remote Command Request 0x17
AT Command Response 0x88
Length
(Bytes 2-3)
Checksum
(Byte n + 1)
MSB LSB 1 Byte
Start Delimiter
(Byte 1)
0x7E
Frame Data
(Bytes 4-n)
API-specific Structure
Identifier-specific Data
cmdData
API Identifier
cmdID
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