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wal

FX3U-485ADP-MB communication

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We use this adapter with FX3U PLC for Mosbus communication. It works, but, if Modbus cable is disconnected it keeps the latest information received. The task is to reset info in such situation and put an error message on HMI screen. I watched the corrresponding error registers and found, that their values do not change whethear the cable is connected or not. Any ideas, what is wrong?

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So you must have a Modbus Driver or server that is talking to the FX3u through the cable. Is the FX3u writing data do the HMI through that driver or server or is the HMI sending poll request to the FX3U. In the first case the FX3u is a master and the driver or server is a slave and it will not know that there has been a problem because it is just waiting for the master to say something. In the second case the HMI (driver/server) is the master and it should report a communiciatons failure. I suspect you are configure like the first case. In that type of configuration you should have a watchdog item that is coming from the FX3U that you know will change at a specific rate and use that to indicate that comms has failed.

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Hi Fred, thank You for the answer. Yes, we are slave and waiting for somebody's orders. As I understood You, there is no build in tools in FX3U, testing if a message received by slave and the only solution is to compare the current and previous values of a signal which is supposed to change itself periodically?

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