PROFIBUS Manual

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Navigation: MS0: cyclic data > Diagnostics

Diagnostic polling

If a controller wants to know the state of a DP slave, it sends an empty SRD telegram, this time to SAP 60. The slave responds with diagnostic information:

Addr	Msg type	Req Res	SAPS	Len	Data
1->22	Slave Diagnosis	Req	62 -> 60
1<-22	Slave Diagnosis	Res	62 <- 60	6	00 04 00 00 00 85

Diagnostics comprise 6 diagnostic bytes and further optional diagnostic blocks.

Diagnosis is requested at the beginning and end of any initialization sequence or when the DP slave requests a diagnostic query through high priority responses:

clip0018

In normal cyclic data exchange the DP slave always responds with a low priority data telegram. When an event requires a diagnostic query, in the next cycle the DP slave respond with high priority. The DP master queries diagnostics and continues with cyclic data exchange.