Hi,

Thanks

 Hello.

MathieuSA

Hi,

I would like to do Modbus RTU, I do not have an RS485 card, only a CPU 1215C with 2 RJ45 ports.

My 1st port is connected to an HMI

Is the 2nd independent or related to the 1st?

And my question, should I install an RS485 card or can I use my 2nd RJ45 port to Modbus RTU

Thanks

You could use the Ethernet port if it was Modbus TCP you are looking for. Modbus RTU however needs the RS485 serial communication card.

You have two options - CB or CM type. I prefer the CB .. a plug-in board that fits directly into the CPU. It is cheaper and connect via terminal connections (not a DB-plug). Terminating resistors are also included in the board.

Cheers

Hello Mathieu;

With more information we can provide better help: What Modbus RTU slave do  you plan on connecting to your CPU?

What serial comms does it support? Do you have access to its Modbus mapping (list of register addresses that contain data for Modbus exchanges)?

Hope this helps,

Daniel Chartier

Hello Mathieu;

Your last post is a bit confusing. Is it correct that you would like to communicate with 6 FC302 drives using Modbus RTU?

First point: you can use either a CM 1241 (RS-485) or a CB 1241 RS-485 with your CPU 1215C, so you have a choice, even if you are using an encoder card:

How do you establish a MODBUS-RTU communication with STEP 7 (TIA Portal) for the SIMATIC S7-1200?

https://support.industry.siemens.com/cs/ww/en/view/47756141

You can install one CB in your S7-1215C, and 3 CMs. You will be able to find the differences between a CM 1241 and a CB 1241 in the Appendixes of the S7-1200 System Manual:

https://support.industry.siemens.com/cs/ww/en/view/91696622

Second point: with a RS-485 comm module or board you can communicate with multiple Modbus slaves, using the Modbus RTU instructions of the S7-1200.Look at this discussion, it might answer most of your questions on multiple FC 302 drive connections:

https://support.industry.siemens.com/tf/ww/en/posts/communication-between-s7-1200-and-danfoss-fc302-how-to-setup-more-than-one-drive-and-how-to-set-the-commands-speed-etc/206062/?page=0&pageSize=10

Hope this helps,

Daniel Chartier

dchartier

Your last post is a bit confusing. Is it correct that you would like to communicate with 6 FC302 drives using Modbus RTU?

 Yes, my drives use the Modbus RTU

I meant that my Drives does not make Modbus TCP, the card is not installed

Sorry for my English