PROFIBUS Manual
If the recipient of a telegram detects an error, the telegram is ignored (binned). Error correction is therefore dependent on the type of service used:
SDN service:
No correction occurs; nor can the sender tell whether any error has been detected by the recipient. An assumption is made that the application is using this SDN service cyclically and that transmission will therefore take place in the next cycle.
The sender expects a response from the recipient within the slot time. If this response does not arrive, either the request telegram or the response telegram has been lost.
Error correction takes place when an unanswered telegram is repeated.
The following diagram shows the sequence in the case of an SRD service, when there is an error in reception of the request telegram.
With the help of the frame count bit (FCB) the recipient can recognize whether it has already received and processed a telegram. Duplicates can be detected and eliminated.
