Communication between M172 and TM172DCL

[jyoon]

Hi,

I am trying to connect TM172DCL (Display for M172) but I keep getting Modbus Comm error.

Current Setting:

1.  I am using RS485-2 as a Modbus Master on M172.

2.  Created a Generic Modbus Device for TM172DCL.

3.  Since they both have the same power source, I left ground disconnected.

4.  Installed 120 ohm to TM172DCL.  Maybe I need to install 120 ohm on M172 as well?

Can you tell me what I am doing wrong?  I need to be able to exchange variables between them but It seems that RS485-2 link on M172 is dead.

Thank you for your help!

Jung

[LeTomas · Accepted solution]

Hi @jyoon ,

When I work with the M172D I usually use it as a master in the communication because for me is much simpler to exchange the information between the devices.

Take a look on this presentation of how to connect both devices (M172 plc as slave): 

https://schneider-electric.box.com/s/ld78b6pxs08l0tb7qgz3eix01hha5wpt

Project: https://schneider-electric.box.com/s/kcwhv7kxtat0shm20njyzzc87azx4dkk

In your case if something is not working you should try to check:

1) The connection from the M172 RS-485 2 to the display (you can check the connection in my presentation but with RS 485-1).

2) The Actual values on the modbus configuration on the M172D and the PLC (They must match).

3) Verify the registers that you want to read from the M172D.

I hope this helps you 👍

[jyoon]

Hi, @LeTomas 

Thank you very much for your help.  I followed it and everything is working fine now.

Jung

[S_Stolyarov]

Thank you for sharing your experience it is very useful, I'll keep in mind this.