Allen Bradley Micrologix 1400 PLC Communication with Yokogawa DCS


Thread Starter


I have 4 Allen Bradley PLCs which are 3 SLCs and 1 CLX This PLCs need to send data to Yokogawa Centum VP DCS. Instead of having and individual Modbus link to DCS, I'm planning to link all 4 PLCs by using Ethernet/IP and plan to buy 1 extra mini PLC which is Micrologix 1400 to become an interface PLC between the 4 PLCs and the DCS. Since the Micrologix 1400 has embedded with an Ethernet port (Ethernet/IP) and Rs485 port for Modbus RTU, the Micrologix 1400 interface PLC will communicate with DCS using Modbus RTU Protocol. Meaning to say, the 4 PLCS will send data to the Yokogawa DCS via interface PLC. The Interface PLC will become translator to translate from Ethernet/IP language to Modbus RTU language.

My question to Expert:

1. Is this setup can works?

2. How to send data inter-PLC by using Ethernet /ip ? Is it just need to grab the tagname or there is an address for that?

3.Is Micrologix 1400 is capable to communicate with 4 PLCs using Ethernet/IP? Or just only 1 PLC?

Curt Wuollet

AB does a pretty good job of making the answers to those questions available in their documentation which is all downloadable. I have not done Modbus with a Micrologix because the needed adapters, etc. cost more than another PLC. But, it should work. IIRC, you can either do direct messaging with the Ethernet IP or exchange blocks seamlessly. It wasn't point and click, but it wasn't difficult. There would be little point to a network that can have only two nodes and I think 4 would be handled easily. It's been a while since I was in AB land, but the EIP stuff worked well. I'm not sure if you could overlay the blocks with Modbus address space, but there is a way to do it, I'm sure. Be sure to check which Modbus instructions are supported.