Application Layer
In DNP3 communication one of the peers is the master and the other behaves as slave. WinCC OA is always the master. In the current version of the DNP3 driver only the master modus is supported as there is no necessity that the WinCC OA driver should behave as DNP3 slave.
DNP3 Point, DNP3 Object and DNP3 Point Type
A DNP3 point is a uniquely identifiable physical or logical entity. It applies to inputs (analog, binaries, counters) and outputs (analog, binaries). A unique DNP3 point is identified by its index and group numbers. The variation describes its data format.
A DNP3 object is an encoded representation of data from a point, or other structure that is formatted according to its group and variation number for transport in a telegram.
A DNP3 point type is a means of categorizing points having related characteristics, similar functionality and relationship to physical hardware or logical space.
Function Codes
A function code describes the purpose and the operation of a requested telegram. Typically the function code is deduced from the object group entry. A variation of the function code is only then required, when more than one function code per telegram is possible (see Defining the Peripheral Address of the DNP3 Driver).
The following table lists the function codes supported by the DNP3 driver.
| Functions | Code | |
| Transfer Functions | Confirm | 0 |
| Read | 1 | |
| Write | 2 | |
| Control Functions | Select | 3 |
| Operate | 4 | |
| Direct Operate | 5 | |
| Direct Operate, no Ack | 6 | |
| Freeze | 7 | |
| Freeze no Ack | 8 | |
| Freeze Clear | 9 | |
| Freeze Clear no Ack | 10 | |
| Configuration Functions | Enable Unsolicited | 20 |
| Disable Unsolicited | 21 | |
Internal Indication
An internal indication is a global group of flags, which automatically are sent in every response. These flags contain information about the status of an outstation and the function codes of the last request.
The information in an internal indication affects only the outstation. For this reason the internal indication is mapped to an internal data point of the corresponding outstation.
