Checksum - Digi XBee Zigbee Mesh Kit User Manual

Start
delimiter Length
1 2
0x7E MSB
Note MSB represents the most significant byte, and LSB represents the least significant byte.
Frame type is the API frame type identifier. It determines the type of API frame and indicates how the information is organized in the Data field.
n
Data contains the data itself. The information included here and its order depends on the type of frame defined in the Frame type field.
n

Checksum

Checksum is the last byte of the frame and helps test data integrity. It is calculated by taking the hash sum of all the API frame bytes that came before it,
excluding the first three bytes (start delimiter and length).
Note Frames sent through the serial interface with incorrect checksums will never be processed by the module and the data will be ignored.
Calculate the checksum of an API frame
1. Add all bytes of the packet, excluding the start delimiter 0x7E and the length (the second and third bytes).
2. From the result, keep only the lowest 8 bits.
3. Subtract this quantity from 0xFF.
Example: Checksum calculation
To calculate the checksum for the given frame:
Frame Data
Start Delimiter Length Frame type Data
7E 00 0F 17
Frame data
Frame
type
Data
3 4 5
API
LSB Frame-type-specific data
frame
type
01 00 13 A2 00 40 AD 14 2E FF FE 02 44 42 -
6 7 8 9 ...
Checksum
Checksum
n n+1
Single
byte