Siemens, Modbus and Honeywell


Thread Starter


First of all, thanks to Anonymous.

Does anybody know, is it possible to connect SIEMENS PLCs to Honeywell DCS (C300 controller) via Modbus Protocol with CP341 or CP 441?
If you are a Honeywell "entitled customer" you can access their knowledge base at Otherwise, you're out of luck. Apparently they don't just answer questions for strangers.

A search of their public knowledge base for the search strings "C300 modbus connectivity" and "modbus" returned no documents.

If you have an Experion C300 system, ask your Honeywell rep. If you're looking at buying one, and you have lots of Siemens PLCs, make sure you have connectivity options in writing in the proposal, or the answer will likely be "no."

The C300 controller and the equivalent version of the Experion PKS DCS is a top-notch, state of the art product. But Honeywell has a history of, well, difficult connectivity with other vendors' products. Even their version of OPC is proprietary to Honeywell... HOPC. That being said, the C300 is a superb controller design and it is far less vulnerable to cybersecurity concerns than any other existing controller. I also like the innovative cooling design. Honeywell did a very nice job on this system.

I would strongly recommend you contact Honeywell's technical support, and make sure that you can connect your Siemens PLCs over Modbus/TCP with the Experion system. There's probably a way to do it via OPC, using a third-party OPC server, but that's the hard way.

Good luck, and please come back and share your results...

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Ganesh V Iyer


It is possible if the Honeywell system supports Modbus ASCII or Modbus RTU since your CP card will only support these protocols. You have to first decide which one should be your master. Normally DCS will be the master and the PLC will be the slave. If DCS is supporting MODBUS TCP then converters are available in the local market. You can use the same.
1. For Scada applications you should connect to the servers and not the controllers like the C300. You can connect via OPC or Modbus.

2. For critical control applications, you should hardwire the signal between the Siemens PLCs and the Honeywell C300 controllers.