MODBUS Communication Between the Intellisys Controller and Siemens PLC


Thread Starter


I need to communicate to the SSR M22-150KW Intellisys Controller with a modbus RTU (RS-485 2 wires). The operator panel is SSR M22-150KW. There is a Intellisys Remote Interface to communicate with SSR M22-150KW controller. I have read carefully the instruction manual of the Intellisys Remote Interface. ADDRESS [Ad], BAUD RATE [bl] and COMMUNICATIONS MODE [CO] exactly the same on the Intellisys Remote Interface and Siemens PLC. Do other settings on the controller needs to be done? Programming is done according register listing with Function Code 03. The IRI's Network port is an RS-485 interface that used in a half-duplex mode. Is this enough? If the network is connected to the Intellisys Remote Interface, Network Port LED is flicker?



The answer varies a lot depending on which S7 PLC family you are using (S7 200, S7 300/400, 1500 etc.)

Please give more details!
Hi Otto VonChriek,

You are right. I used S7-400H with CP341. Currently LED TXD flashes on CP341, Because the CP341 is configured properly done and modbus RTU function works correctly. This work is already done for Ultrasonic Gas Flowmeter (MPU1200). The problem now is that the using the Modbus poll does not get a response from the Intellisys Controller, and the following message (Read Error) is displayed by Modbus poll. My question is that if the cable is connected (RS-485 Half-Duplex), CP341 receives a response from the Intellisys Controller? I tried to be connected to the Intellisys Controller with Modbus Poll, and registers it to be read but I have not been successful so far.

Thanks a lot
Hi Ehsan,

independently of the PLC type, you should get flickering lights on the Tx and Rx, if not, that means the communications aren't done properly.

Logically you need code on the master of the Modbus to read/write values on the slave and you need proper set up in place to create and configure the Modbus in both. But, once is done and the wiring is connected, yes, you should see Tx and Rx flickering.

Hope that helps,