Calm_down

Hello Begho,

well, this is not that easy to answer but I think there is only one question to answer: Which IO Bus will you use?

If you use PROFIBUS you just need either a CPU with PROFIBUS Interface or you need a CP with PROFIBUS Interface, like the CP 443-5 Extended (S7-400) or the CP 342-5 (S7-300). I choose these modules because I guess if you use PROFIBUS you will use the DP Profile.

If you use MODBUS it is a bit more difficult. This is due to the fact that SIMATIC is not supporting MODBUS by Standard. To get it to work you will have to use a serial CP, like the CP 441-2 (S7-400) or the CP 341 (S7-300) plus a certail MODBUS Master Driver to be additionaly installed.

I hope I could help you a bit.

Stay calm.

 I just bumped into your comment here several years after you posted it. That triggers something in my mind. We have the same kind of setup at the industry I work for. We have S7 400 PLC on PROFIBUS with S7 300 distributed peripherals. Then communication to the sepams is through CP 341 which sits on the same rack as a Profibus ET200M. I came many years after the system had been installed. I am just wondering how such a CP is configured. Please advise me on this. Thank you.

Hello Kiiza;

See the information in the last part of this FAQ, concerning the ET 200M integrating a CP 341 as Modbus RTU Master (or slave)::

Which hardware and software components do you need to establish communication between SIMATIC S7 stations and third-par ty devices using the MODBUS RTU protocol?

https://support.industry.siemens.com/cs/ww/en/view/58386780

When you insert a CP 341 in a ET 200M configuration, the configuration of the CP only selects a number of bytes reserved for the exchanges between the Profibus master and the CP 341. This number of bytes (8, 16 or 32 bytes, depending on your communication speed requirements over Profibus-DP) has nothing to do with the number of bytes exchanged between the CP 341 and the Modbus slaves it is communicating with; these are programmed through the Loadable Driver you set up on the CP 341. It is simply to create a channel between the CP and the Profibus master.

You then have to program the Modbus functions (made available through the Loadable driver and the dongle to be placed in the backside of the CP 341) in the CPU that acts as a Profibus master.

Hope this helps,

Daniel Chartier

Hello,

if I can give addition to Daniel's perfect info, also (in my opinion) you must be careful to have ET200M that support also communication modules, so I have my one ET200M which is old and also DPV0 module and one new Et200M  which with it's version support simply hope all modules (as is described in description of module in HW cfg), also communication. This I want give to this discussion, maybe important info for first.

JBUS, for most practical purposes, can be handled as Modbus.

Historically, there was a licensing issue prior to Modbus becoming an open protocol, so JBUS deviated from the Modbus spec slightly.   The differences are so minor that in most cases Modbus can be used successfully.

The best summary of the differences between JBUS and Modbus are on a Software Toolbox web page:

http://support.softwaretoolbox.com/app/answers/detail/a_id/3402/~/jbus-protocol-vs.-modbus-protocol

In case the link above goes bad over time, the details from that page are on this graphic image:

https://s13.postimg.org/v6uggcgtj/Software_Toolbox_table_for_JBus_vs_Modbus.jpg

One must be aware of JBUS' one based register addressing vs Modbus' zero based addressing.

But unless the JBUS unit uses the slightly extended addressing scheme, Modbus should be able to address it.