Author Topic: FMD88-10 PLC's MODBUS TCP client malfunctioning  (Read 1302 times)


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FMD88-10 PLC's MODBUS TCP client malfunctioning
« on: May 10, 2019, 02:44:10 AM »
I have FMD88-10 PLC I wanted to perform Modbus read and write operation form this PLC for monitoring and control purpose. I have one Fronius solar Inverter and one Sinexcel Battery Inverter both are connected with PLC using Modbus TCP protocol. The ladder logic is written in this way that performing read and write operation in a continuous manner with respect time like in a never-ending loop. but PLC can able to perform read and write operation in these two devices one time means at the first time or the first cycle is able to read the value from Modbus register of that device but in next cycles, it was unable to fetch data from those devices.

I didn't find any reason behind this,  why it is behaving like this? I have attached my PLC code with this message. Please help me to find the error and its solutions. Thank You.


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Re:FMD88-10 PLC's MODBUS TCP client malfunctioning
« Reply #1 on: May 11, 2019, 12:20:05 AM »
Each time when you make a Modbus TCP connection to the (3rd party) Modbus TCP server you have to wait for the connection to be made before you can run the READMODBUS or WRITEMODBUS command successfully.

Since you have two Modbus TCP server devices and there is only one client port on the FMD PLC, you have to make a connection, check that the connection is successful, the perform the READMODBUS or WRITEMODBUS command, then check STATUS(2) to ensure that you get a good result. Finally close the connection. You then connect to the second device and you must do the same by checking that the connection is made then READ or WRITEMODBUS command, check the communication status, then close the port.

It can be done on the fly reasonably fast especially the the devices are all on a LAN.

Tel: 1-877-TRI-PLCS