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Technical support / Re:Problem in Modbus RTU communication between FMD88-10 and Wooward MRA4 relay
« on: September 19, 2017, 03:26:23 AM »
You did not specify what was the problem.
Anyway, as per our previous post if you have some doubt about communicating with a 3rd party Modbus slave, always use a PC based application such as the Modbus Poll software to test your hardware. Once you get a successful communication you would have figured out most of the parameters required for a successful communication, such as the actual binary address, the function and the communication parameters.
For RTU another way to troubleshoot the communication problem is to use a PC to monitor the communication packet exchange between the PLC and the Modbus RTU slave. What you need is a USB to RS485 adapter (e.g. the U-485) and connect to the RS485 bus between the two devices, then download and run a terminal emulation software to monitor the comm. One good and free software is the RealTerm software that can display binary data exchange.
Anyway, as per our previous post if you have some doubt about communicating with a 3rd party Modbus slave, always use a PC based application such as the Modbus Poll software to test your hardware. Once you get a successful communication you would have figured out most of the parameters required for a successful communication, such as the actual binary address, the function and the communication parameters.
For RTU another way to troubleshoot the communication problem is to use a PC to monitor the communication packet exchange between the PLC and the Modbus RTU slave. What you need is a USB to RS485 adapter (e.g. the U-485) and connect to the RS485 bus between the two devices, then download and run a terminal emulation software to monitor the comm. One good and free software is the RealTerm software that can display binary data exchange.