difference between modbus protocol


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Presently it is connected with FOXBORO DCS thru Modicon Gateway 30 for data transfer. As per details available with us, the protocol used is MODBUS Gould 584 RTU and the configuration settings used are Baud 19200, data bit 8, Parity Even, stop bit 1.

This set up is in line since from 1996 and is working perfectly ok.

Up-gradation of AS:

Now the present AS is under up-gradation and so as a part of it, the Modicon Gateway 30 will be replaced by new gateway (FDSI) module FBM231 which supports Modbus RTU as well as Modbus ASCII protocol.

Problem faced:

When we connect the ICS MUX as a slave to FOXBORO with FBM 231(FOXBORO module) it shows online in the AS (FOXBORO) but we are unable to get the DATA in the AS(FOXBORO).

From the system diagnostic of Foxboro it can be said that, the communication between FIeldbus system and AS is established but the data is not available to the AS.

We have also connected one PC having modbus simulator with ICS MUX with above settings but we could not able to get any data, however if we connect the simulator to AS (FOXBORO) we can able to get the data.