How to communicate via the RS485/2 communication port on the Modicon M172 PLC?

[MaizaVitoriaCosta]

I'm using a chiller with Modbus RTU communication. I tested direct communication between the chiller and a Modbus RS485 to USB converter. It worked perfectly using ModScan.

However, this chiller is not communicating with the RS485/2 port of my M172 PLC. I checked all the settings on the PLC and I don't see any configuration errors.

And on my RS485/1 port, I use an HMI (model HMIET6401). This data from the chiller will be received by the M172 PLC, which will consequently send this data to my HMI. Can anyone help me? I've tried everything.

[FedericoM]

Hello,

some hints.

Check the value of:

Have you done a download all with reboot?

Check also the status of the following target variables:

[MaizaVitoriaCosta]

Good evening. The "MbMRTU_DisByPar" item is enabled in the Miscellaneous tab. And yes, every time I send the program to the PLC, I restart it (unplug it from the power outlet and disconnect the USB cable).

Regarding the status items you mentioned, how would you perform a "MOVE" to identify those statuses? Do you have an example?

[FedericoM]

Drag & drop variables into the watch window, the index of the array is the node number you have specified on the slave when you have declared it in the Configuration section.

[MaizaVitoriaCosta]

Good morning. I did it here. What does "FALSE" mean? See if it's correct, the images follow... the variables aren't matching.

[FedericoM]

I need to see the entire sysMbMrtuNodeStatus[11] in the watch window to better understand the situation.

If miss is false and pres is true, it works.

[ismailozinan · Accepted solution]

Hi,

sample link is here 

I am sharing the folder where I placed the sample communication program link and the video link demonstrating Modbus communication using the TM221 PLC W50 (40051) and W51 (40052) addresses.

The M221 PLC operates as a slave device, similar to your chiller unit. You may proceed with your implementation by considering the M221 as the chiller and following this sample program.

I recommend downloading the program once using the Download All option. After confirming that your Modbus parameters are correct, please ensure that the USB cable is not connected to the PLC, then power cycle the PLC. Afterward, you may go online with the PLC.

I hope this will be helpful.

Best regards, and I wish you successful work.

[ismailozinan]

Hi,

is it possible try attached methods.

I am currently using the XBTZ9008 cable by cutting the RJ45 end and connecting only the Modbus A and B terminals to the TM172. This method works properly.

Although some people prefer to assemble the cable manually, I do not recommend this approach. There are specific pins inside the cable that need to be short-circuited. If this is not done correctly, it may cause issues, especially with non-isolated devices.

Thanks.