User Manual

Operate in API mode API mode overview

XBee/XBee-PRO S2C 802.15.4 RF Module User Guide

Frame fields Byte Description

Length 2 - 3 Most Significant Byte, Least Significant Byte Characters escaped if needed

Frame Data 4 - n API-specific structure

Checksum n + 1 1 byte

Escape characters

When sending or receiving a UART data frame, you must escape (flag) specific data values 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. If not escaped, 0x11 and 0x13 are sent as is.

Data bytes that need to be escaped:

n 0x7E – Frame Delimiter

n 0x7D – Escape

n 0x11 – XON

n 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 previous 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.

Start delimiter

This field indicates the beginning of a frame. It is always 0x7E. This allows the device to easily detect a

new incoming frame.

Length

The length field specifies the total number of bytes included in the frame's data field. Its two-byte

value excludes the start delimiter, the length, and the checksum.

Frame data

This field contains the information that a device receives or will transmit. The structure of frame data

depends on the purpose of the API frame:

Start

delimiter Length

Frame data

Checksum

Frame

type

Data

1 2 3 4 5 6 7 8 9 ... n n+1

0x7E MSB LSB

API

frame

type

Data

Single

byte

n Frame type is the API frame type identifier. It determines the type of API frame and indicates

how the Data field organizes the information.