RS 485 communication problem

[Himanshu]

I am having PLC S7 200 smart model- ST 30 .
In which I am getting problem in modbus communication of PLC and VFD via built in RS 485 port of PLC.
PLC is not able to communicate also PLC RS 485 port is heating during communication. What could be the possible reason of this problem and what can I do?

 

[AlfredoQuintero]

Hi and welcome to the group. In serial communication whenever things do not work I recommend reviewing the basics. Check the cable and pin assignment for both interfaces and confirm correct cabling. Also, if there is no termination you should add it. It may have worked in the past without termination in marginal conditions, but whatever changes in the setup you are experiencing communications may not work without termination. Also, check whether the baud rate settings were changed.

 

[Himanshu]

RS 485 problem

ok i will try it. Actually i was not using termination because i have another plc ST20 which is communicating properly.
but sure i will try it.

 

[AlfredoQuintero]

Good luck and please keep posted. Hope you find your solution.