GE Mark V - HMI or <I> - Foxboro MB30 in MODBUS Multi-drop


Thread Starter

Won Chul Shin

GE <I> manual for MODBUS part explains only single-to-single connection, and GE Industrial Service told us their system doesn't support multi-drop link.
We're working on Cogen plant with GE Mark V and HMI (GE brand name) monitoring system. We planned to hook up one HMI and 3 or 4 other Modbus slave devices in a multi-drop Modbus link. But as mentioned in Summary, GE is saying that it's not supported, and I could not find any hard evidence that we can use RS-232/RS-485 converter and just put HMI in the multi-drop link.

As my understanding if you have any device can talk to Modbus protocol you can hook it up in the multidrop RS-485 communication link.

But I could not find any solid evidence in Modicon Modbus Protocol Reference Guide, PI-MBUS-300, Rev. J that my field proven experience is right.

If there is anybody who has experience with GE <I> station or HMI station with Modbus multidrop interface to DCS system, please let me have some advice and idea.


Won Chul Shin, P. Eng.
Senior Controls Engineer
Fluor Canada Ltd.
(403) 298-4988

Dean Kindrai

I don't have experience with that particular HMI, but I do have experience using MB in a multidrop mode. The issue I have seen is that many HMI's will not allow you to configure their respective drivers to have multiple addresses assigned to a single COM port.

One option - not the most economical, but it will work, is to switch the HMI to a Modbus Plus driver, install an SA-85 card in the PC, and run a piece of cable to a Modicon NW-BM85-000 Bridge Mux. The Bridge Mux supports multidrop Modbus, while the SA-85 driver will support multiple addresses mapped to a single driver.

Won Chul Shin

Thank you for your reply.

GE have two different kind of PC monitoring system for GE Mark V GTG control system. One is <I> station and the other is called "HMI". "HMI" is GE's brand name.

Tom Anderson

Did you find a solution to this? I am working on a project that requires monitoring two Mark V's and some PQM's on a single Modbus channel. We are
using Wonderware as the HMI (SCADA). My plan is to simply use an RS-232 to RS-485 converter, as you were thinking.

Your ideas or results would be appreciated.

Did you find a solution on how to interface four GE HMI to one foxboro MB30? I have the same situation and i would like to know if you have a solution.

Elvin Pagan

Magdi M. Abdel Halim

Foxboro has two main options to communicate with Mark-V :
1. Using DI30 (Device Integrator 30) with Mark-V protocol.
2. Using Mark-V protocol for AW70 via Ethernet.