Applies To:
  • CitectSCADA 5.xx

Can Citect communicate to I/O devices via the Profibus DP protocol? 

You can use an OPC Server for Profibus DP and the OPC client in Citect. A German company, Softing, sells an OPC Server for Profibus DP that allows you to connect to a maximum of 125 DP slave devices. A trial version can be downloaded from the company's website ( It requires a Profiboard as its PC interface board to connect to the Profibus DP network (the Profiboard can also be used to connect to a Profibus FMS network). Windows NT is required to use the Profiboard.

On the bus, the OPC Server for DP can act as a DP master, class 1 and class 2. Class 1 functionality allows input and output values to be both read and written; class 2 functionality allows values to be read only. Class 2 is applied whenever a master class 1 already exists in the network and is used to intelligently configure the OPC server name space.

The following data types are supported:

DP Slave (tags): Bit, byte, word, dword, BCD (2, 4, 8 digit), real

OPC item: Signed16, Signed32, 4 byte float, 8 byte float, boolean, byte, bytearray, visible string

After installing the Profiboard, the OPC server can be started. You will see a tree structure in the left part of the window. The first element that has to be added to this tree structure is a Profiboard card. You can have up to four Profiboards in a PC. In properties you can see if the installed Profiboards are recognised by the OPC Server.

The next element (node) that is added is a Profibus DP Master. In the properties of this master you can set the station address and the baud rate; it also has an option (Quickstart) that allows an automatic search for DP bus participants.

The next element (node) that is added is the Profibus DP Slave device. If you have done a Quickstart, this should appear automatically. In the properties of the slave node you can set/see the station address. It also has options to read the slave configuration on-line or to import the slave configuration from a GSD file.

The last step is defining tags in the OPC server.

Once the values are available in the OPC Server for DP, it is easy to get those values into Citect via the OPC Client driver.  Set up an I/O device as OPC Client, and specify the right address for the OPC Server (Softing.OPC_DP) in the I/O Device form. Then define the right address for the variable tags (for example: Profibus_0.Master0.Slave0.Tag01). The tag address has to be the full address, with all the defined elements shown (Profiboard, Master, Slave, Tag).

The automatic determination of bus participants and the automatic reading of the slave configuration via the bus make this OPC Server for DP a very user friendly tool.