Appendix A.12. FieldServer DNP Node Number

FS-8700-47 DNP 3.0 Driver Manual	Page 37 of 51

Appendix A.11. Controlling the DNP 3.0 Driver’s Qualifier

The protocol uses a qualifier in the application layer part of a message to indicate how data must be packed in the message. The DNP 3.0 Driver as a Client will default to use a Qualifier of 1. The qualifier is used internally by the driver and is of no concern unless the DNP protocol has been implemented to require the use of qualifiers other then 1. In this case it is possible to change the driver’s default value by specifying the dnpQualifier parameter. For example, to address a Control Relay Output Descriptor object in a Multlin 489 Generator management relay, the vendor data sheet indicates that only qualifiers 17 and 28 may be used.

When the driver is configured as a Server then the dnpQualifier parameter specified in the CSV file is not used. The qualifier of the requesting poll is used in interpreting the request and forming the response. The driver accepts poll’s that have the DNP qualifier set to 6 which effectively requests the Server to send back all objects of the type requested. The driver’s support for this qualifier is limited by the length of the response message. The response must fit in one 255 byte message. The number of objects contained in the response message (and hence the length of the response) is controlled by the length parameter. We have found lengths in the upper range 10 to 30 successful.

As a Server, if configured to serve ‘changed’ data the driver may choose the qualifier itself as the data object may be non sequential. See 5.3.8.