Modbus RTU to Profibus DP Conversion?


Thread Starter

James Wilson

I want to be able to use an MMI software package like Siemens WinCC to log production data from 2 different PLCs on different networks. One network is Profibus DP and the other is Modbus RTU. There is an extra slot in the Koyo PLC that I can use but none in the S7, but Koyo does not have a Profibus module. What would be my best option?
Your software package (WinCC or other) probably has both a Profibus-DP and Modbus RTU driver available allowing you to create tags from both networks.

Alternatively, if your HMI software does not have both drivers, you can use an OPC Server with both Profibus-DP and Modbus RTU, and then create OPC tags on your HMI.

Daniel Chartier

Hello James;

Here are a few suggestions:
1) You don't mention the PLC models you are using, so I'll just point out that the Koyo DL05/06 have a Profibus-DP slave module (H0-PSCM) that you could use to connect to the S7 DP-master system, and from there connect to WinCC.

2) In case you have a Koyo model that doesn't support Profibus-DP directly, you could set up a gateway from Modbus RTU to DP-slave, such as the one found here (Google for "Modbus to Profibus gateways", there are many manufacturers):

3) You could buy an add-on Modbus channel for WinCC from Allmendinger; see their website at:
You would connect to WinCC through the serial port for Modbus (the Koyo PLC) and through whatever hardware you have for the Profibus channel (the S7 PLC).

4) You could buy an OPC server for Koyo's DirestSoft (PC-KEPPLC OPC server from Kepware comes to mind) and connect the Koyo data to WinCC using the OPC channel:

Hope this helps,
Daniel Chartier
Dear James,

Please send me other details, i.e. baud rate, what configuration you are using to connect both PLC.
As accordingly you can use it, i.e you can use two com ports in PC to connect both PLC to one HMI.


You can convert RS232 to Modbus and can use PLCs in multi drop and use Modbus driver for your SCADA.

Jason L. Block

Hi James,

Assuming that WinCC would use Profibus as the main network of interface, you could use a gateway that would talk Modbus RTU to the Koyo PLC and then convert the data to Profibus.

HMS Industrial Networks makes a gateway called the Anybus Communicator for Profibus that will handle this application.

Information can easily be found at

Best Regards,
Jason L. Block
HMS Industrial Networks, Inc.