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Operate in API mode
1. Add all bytes of the packet, except the start delimiter 0x7E and the length (the second and
third bytes).
2. Keep only the lowest 8 bits from the result.
3. Subtract this quantity from 0xFF.
To verify the checksum of an API frame:
1. Add all bytes including the checksum; do not include the delimiter and length.
2. If the checksum is correct, the last two digits on the far right of the sum equal 0xFF.
Example
Consider the following sample data packet: 7E 00 0A 01 01 50 01 00 48 65 6C 6C 6F B8
Byte(s)
7E
00 0A
01
01
50 01
00
48 65 6C 6C 6F
B8
To calculate the check sum you add all bytes of the packet, excluding the frame delimiter 7E and the
length (the second and third bytes).
7E 00 0A 01 01 50 01 00 48 65 6C 6C 6F B8
Add these hex bytes:
01 + 01 + 50 + 01 + 00 + 48 + 65 + 6C + 6C + 6F = 247
Now take the result of 0x247 and keep only the lowest 8 bits which in this example is 0x47 (the two
far right digits). Subtract 0x47 from 0xFF and you get 0xB8 (0xFF - 0x47 = 0xB8). 0xB8 is the checksum
for this data packet.
If an API data packet is composed with an incorrect checksum, the XBee/XBee-PRO SX RF Module will
consider the packet invalid and will ignore the data.
To verify the check sum of an API packet add all bytes including the checksum (do not include the
delimiter and length) and if correct, the last two far right digits of the sum will equal FF.
01 + 01 + 50 + 01 + 00 + 48 + 65 + 6C + 6C + 6F + B8 = 2FF
API frames
The following sections document API frame types.
XBee®/XBee-PRO SX RF Module User Guide
Description
Start delimeter
Length bytes
API identifier
API frame ID
Destination address low
Option byte
Data packet
Checksum
API frames
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