Siemens 1200 as a Modbus RTU slave and PC as a master

[Catnip]

I am trying to get Siemens 1214c dc/dc/dc cpu work as a Modbus RTU slave with RS232 communication module. As a master i have PC.

I tried to get the connection work according these instructions:

https://support.industry.siemens.co...ortal)-for-the-simatic-s7-1200?dti=0&lc=en-WW

I didn't create the mb_master-block, since I don't have two PLCs communicating. As i try to send data to PC I only get errorsignal from mb_slave bloc, announcing about invalid port id (code 8180). The port id is the same as it is in the port configuration, so I really don't understand this. Could someone please help me to understand why my connection is not working?

 

[harryting]

I don't know much about Siemens PLC but all modbus slave should work the same way. When you say PC, exactly what software is used and what physical connection do you use (RS485, RS233, ethernet?)

The problem could be physical (cable, pinout) or on the software side. Eliminate one issue at a time.

 

[Lare]

Have you downloaded hardware config?

MB_load needs to call only at start of PLC or error.

Is rx led blinking when you make query from PC?

 

[adfox]

Run mbconfig on first scan to set up comm, check if rx-tx needs to be changed.
Most modbus problems was with proper rx-tx swap