Hello,

Im quite new in the Siemens S7-1200 field and I have a problem with connecting to a rectifier through RS485 connection. I have S7-1200 with CM1241 RS422/485 module.

I have managed to create program to connect to my PC through USB-RS485 dongle and I have no problems with reading and writing to holding registers. But the type of connection to the rectifier is very confusing.

As you can see in the PDF file there are no registers where I can write, but entire commands to be send to the rectifier and I am at loss what and how to do it. On the rectifier I have set bit rate of 9600, ID of 5 and type of connection Modbus RTU.

I need to send the working voltage, time and start command. And I have to return current, voltage, status and errors. No matter how I do it, I cannot connect or control the rectifier.

Also the module CM1241 I have is 2-wire RS485 but the rectifier looks for 4-wire RS485, is this possible to connect.

Have any of you used this type of connection ? I am very confused right now.

Thank you for the support

danw

The manual states that it works with full duplex RS-485, which is 4-wire RS-485.  Modbus RTU is half duplex and can run on 2-wire RS-485.   Make sure the Siemens comm module supports 4-wire, full duplex communication before you dive in too deeply.

FYI .. The S7-1200 product range does not offer a 4 wire (full duplex) RS485. Only a 4 wire RS422 is on offer which is not dirrctly helpful.

Thank you very much for the fast response and the help in the matter.

I will contact the manufacturer if we can figure something about the Modbus RTU.

Best regards

NimiDoti

Thank you very much for the fast response and the help in the matter.

I will contact the manufacturer if we can figure something about the Modbus RTU.

Best regards

 I Have the same problem, if you have any news and can you share it?