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. A checksum is a calculated value using a cryptographic hash function to verify the integrity of data, such as a binary file. If an API data packet is composed with an incorrect checksum, the XBee/XBee-PRO Zigbee RF Module will consider the packet invalid and will ignore the data. 0x3B is the checksum for this data packet. Subtract 0xC4 from 0xFF and you get 0x3B (0xFF - 0xC4 = 0x3B). Now take the result of 0x01C4 and keep only the lowest 8 bits which in this example is 0xC4 (the two far right digits). 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):Ġx08 + 0x01 + 0x4E + 0x49 + 0x58 + 0x42 + 0x45 + 0x45 = 0x01C4 If the checksum is correct, the last two digits on the far right of the sum equal 0xFF.Ĭonsider the following sample data packet: 7E 00 08 08 01 4E 49 58 42 45 45 3B Byte(s) View ImageUDP calculation test and method of calculation and IP datagram header checksum method is similar.Add all bytes including the checksum do not include the delimiter and length.Keep only the lowest 8 bits from the result.Add all bytes of the packet, except the start delimiter 0x7E and the length (the second and third bytes).To calculate the checksum of an API frame:
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