CB1241 RS485 Board LED's not lighting up with S7-1200 1215C

[integration]

Hi all,

I am trying to do Modbus communications via the CB1241 RS485 Communication Board on a Siemens S71200 PLC. I am using a 1215C CPU. After configuring the hardware and writing a program for the MODBUS communication I can successfully compile and download to the PLC. However, the LED indicators for RxD and TxD on the communication board do not light up.


I have checked my configuration and when I take the PLC online I can verify via TIA Portal that the PLC has recognized the module however it just is not transmitting and receiving data since the LEDs aren't lighting up on the board. In my program, the functions "MB_COMM_LOAD" and "MB_MASTER" both have no error and have a 16#0000 Status. Any ideas on what the issue could be or where I am going wrong?

 

[integration]

Hi all,

I am trying to do Modbus communications via the CB1241 RS485 Communication Board on a Siemens S71200 PLC. I am using a 1215C CPU. After configuring the hardware and writing a program for the MODBUS communication I can successfully compile and download to the PLC. However, the LED indicators for RxD and TxD on the communication board do not light up.


I have checked my configuration and when I take the PLC online I can verify via TIA Portal that the PLC has recognized the module however it just is not transmitting and receiving data since the LEDs aren't lighting up on the board. In my program, the functions "MB_COMM_LOAD" and "MB_MASTER" both have no error and have a 16#0000 Status. Any ideas on what the issue could be or where I am going wrong?

I have also read online that in some scenarios the board on the 1215C CPU where the CB1241 module is placed can become non-functional if the module was accidently placed when the PLC was still powered and I wonder if this could be the case. I am using TIA Portal V17.

 

[tarik1978]

These LED's illuminate only when data is being received or transmitted by the communication port, which device the board is communicating to?

 

[integration]

These LED's illuminate only when data is being received or transmitted by the communication port, which device the board is communicating to?

The board is communicating to a Vaisala WXT536 Weather Station. How can I get data to be received or transmitted by the port if I have set it with the appropriate settings ?

 

[tarik1978]

Check the address of WXT536, the default is 1.
Try swapping RS485 wires.
Check the termination resistors.
Make sure that the firmware of WXT536 is 3.85, or newer.

 

[tarik1978]

Make sure,the parametre MODE in the instance data of the "Modbus_Comm_Load" is set to 4 (half duplex RS485).


Check that the attribute "optimized bloc access" of data bloc DB14 is disabled.

 

[tarik1978]

The %DB10.DBX0.0 is true only one scan, you need to set another bit based on comm load done bit