EIOC connection to Modicon Quantum PLC via MEBII Modbus TCP/IP

DV 13.3.1.  EIOC has Modbus TCP/IP driver installed.  When I HTTP to the MEB unit, I can see that the MEB is device 3 and there are connections to 2,11,14,19 & 43.  My Quantum configuration in Concept shows my PLC device ID to be 11.  I can't get a connection to the PLC via the EIOC with a holding register setup.  It says no device com.  This is our first EIOC, but I am very versed in VIM and serial modbus RTU/ASCII and modbus Ethernet IP connectivity in general. 

When I use the MEBII register viewer, I can see registers changing in the modbus table but they don't correlate to my ModbusPlus registers in the PLC.  I have devices 2,3(MEB),14,19 & 43 connected to the system and 2,14,19 & 43 are wonderware PC's (non modbusplus utilizing the MEBII for comm). I put in a GSC call and their response was no information available.  I have tried broad scope register setup and single point register setup for coils, inputs & holding registers and same "no communication" status in DV Diagnostics with a bad status.

In search of anyone who has made this connection successfully to provide some insight.  Thanks...JWB

  • A quick Google search reveals that "Modbus Plus is a peer-to-peer protocol designed for high-speed communication, while Modbus TCP is an Ethernet-based protocol that allows for broader connectivity and integration."

    The response goes on to clarify that Modbus TCP is a Master/Slave architecture while Modbus Plus is Peer to Peer allowing devices to communicate directly. Modbus Plus uses a Token-Passing topology, which the EIOC will not support.

    So, I think you will need a protocol converter, if one exists, or maybe a data concentrator that can exchange data with your devices and expose it in a Modbus TCP format for the EIOC to work with.

    Andre Dicaire

  • In reply to Andre Dicaire:

    Andre, that is where the MEBII fits into the equation. It acts as the gateway to convert Modbus+ to Modbus TCP/IP.
  • The EIOC P01 has an IP address assignment in DeltaV explorer. I was in the wrong IP scheme between the EIOC and the Modicon. Now they are in the same scheme, it connected instantly and is communicating. For referenence for anyone in the future, the Device ID is the PLC device address, not the MEBII device ID. Sometimes it's the simple details that matter the most. Have a great day!
  • In reply to Jason.Brumfield:

    Thanks for confirming those details. Much appreciated and I learned something today.

    Andre Dicaire

  • In reply to Andre Dicaire:

    Thanks for posting the problem and correction Jason. There are a lot of simple solutions out there. They are just hard to find - especially when the pressure is on.