Created Date: November 30,2011

Created by: franji1

The MB Gateway is a relatively new product and is designed for this type of networking.

Modbus/TCP supports this "gateway " type of addressing where you specify a "router " or "gateway " IP Address, but then embedded in the Modbus request is the specific RTU Unit ID. The MB Gateway "peels off " the TCP Transport Layer then puts it in a serial Modbus packet to that Unit ID out the 485 port. Then the response from the PLC does the opposite operation by reformatting the RTU packet as a valid Modbus/TCP response.

Make sure you can set the Unit ID (a.k.a. slave ID) in your HMI software when using its Modbus/TCP driver "connection ". This is a number between 1 and 254. It probably defaults to 255 (maybe 0), but you need to set it to the RTU slave ID of your Click.

You could have multiple Clicks or other Modbus/RTU slaves hanging off your 485 network, and each of those would have to have a different Unit ID (e.g. 1, 2, 3). Then, in your HMI software, you could set up a tag to talk to PLCA Input 16, PLCB Output 12, where PLCA is configured to (for example) Modbus/TCP address 192.168.12.20, Unit ID 1, PLCB is configured for Modbus/TCP address 192.168.12.20, Unit ID 2, where your MB gateway's IP address is 192.168.12.20, for example. Now, your HMI, using Modbus/TCP, can talk to mulltiple PLC's through the MB Gateway.