PROFIBUS Manual

The FCS (Frame Check Sequence) checksum required in the telegram for Hamming distance 4 is always located directly in front of the end delimiter (ED) and has the following configuration:

For the without-data format (SD1) the checksum must be formed by the arithmetical sum of DA, SA, and FC without start delimiter (SD) or end delimiter (ED) and disregarding sums carried over. For the fixed length format with data (SD3) and the variable length format (SD2) the checksum must also include the payload (PDU).

Example of bytes added together in the FCS:

See also the section on Error handling.