Frequently asked questions
Is TM171ARS485 compatible with a M173 controller?
FAQ000281326
05 May 2026
Query
Is TM171ARS485 compatible with a M173 controller?
How can I get additional Modbus ports with M173 controller?
Answer
The TM171ARS485 module is not compatible with M173 controllers. As per the below table, the TM171ARS485 is only compatible with TM171P, TM172P and TM172O controller ranges.
The M173 controller does not support any communication modules that would offer RS-485 expansion.
You may note that there is a physical connector to communication module observed on the M173, however this is in fact for secure Wi-Fi interface connection as seen in the screenshot attached.
Alternatives
Option 1: If an additional modbus port is needed, an alternative solution could be to use a TM172SIP plug-in connected to the pin strip of TM173O, in order to have one additional modbus TCP port in the ethernet port.
Option 2: Another solution could be to use one TM172 18 I/O with TM171ARS485 in order to have three RS-485 ports.
Option 3: For 4 RS-485 ports, the solution could be to use two TM172P 18I/O connected in binding via CAN port or Modbus TCP.
Option 4: For 6 RS-485 ports, the solution could be to use two TM172P 18I/O connected in binding via CAN port or Modbus TCP and for each PLC a TM171ARS485
Please note, for the last two options, you will need to ensure the two databases are aligned for R/W.