Hello,

I am trying to establish Modbus RTU communication with a PLC S7-1200 G2 (6ES7 212-1AG50-0XB0, firmware 1.0.2) in TIA Portal V20 Update 3 (with all latest HSPs installed), using either a CM 1241 (6ES7 241-1EA50-0XB0) or a CB 1241 (6ES7 241-1CA50-0XB0), but so far without success.

In the program I am using the standard Modbus blocks Modbus_Comm_Load and Modbus_Master.
For testing I use Modbus Poll on a laptop as the Slave (I have also tried with a real device, but the result is the same).

• With CB 1241: Tx and Rx LEDs are blinking, Modbus Poll receives the request and sends a response, but Modbus_Master returns error 81E2.
• With CM 1241: Tx LED blinks on request, but Modbus Poll does not receive any data, and Modbus_Master returns error 16#80C8.

Communication settings: 9600 baud, Parity = none, 1 stop bit.
I have verified the settings, and the same configuration worked previously with a CPU 1215C AC/DC/Rly + CM 1241 (RS422/485) without any problems.

Question: What could be causing this issue with the S7-1200 G2?

Thanks in advance for your help.

Thank you!  MODE = 4 really helped; I was not aware of this mode. Previously, we used the first-generation S7-1200 with CM 1241, and it was sufficient just to select the mode in the hardware configuration.

New question published by Thai_DHID is split to a separate thread with the subject PLC S7-1200 G2 Modbus communication problem: modbus_comm_Load block Done pin not true.

Best regards
Moderator_Lan