![]() TCP in general is really peer-to-peer, but with Modbus our Master (openHAB) becomes a TCP Client, initiating communications with TCP… In Modbus-TCP, we use the standard TCP/IP communications protocol as a “carrier” for our Modbus flavoured data transactions. ![]() Paying attention to the TCP section - reduce your connect/disconnect overheads by settings in the Modbus binding. It is however more likely to be serial side problems. ![]() If a serial transaction messes up, this gateway cannot tell you about it, and just fails the TCP transaction. It would be nice to inspect the gateways serial error log … but I don’t think it keeps one. Your settings for RS485 look reasonable, and I assume match the real slave device. RS485 wiring bus should in theory be terminated with a 120R resistor at both ends. In reality, you can “usually get away with” one for short wiring runs, or even none for very short. “Short” for RS485 is relative - a few metres is short, but I would do it properly once we get into tens of metres or more than two devices on bus. If in doubt, check with a meter between A and B (gateway powered off, disconnected from bus) This USR box includes a terminator resistor, I think it can be selected by internal link on the PCB, but is enabled from the factory.
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