We are facing the same issue. We are trying to retrieve data from the Acuvim-L power meter using RS485. We have tried everything, e.g. switching the port, the IoT2040, the cable and every software settings, and it just doesn't work. Sometimes it's timed out, and sometimes it throws a modbus exception 3. When we use an RS485 to USB converter it just work like a charm.

It is frustrating since we rely on the IoT2040 to be a robust data logger, and we always dislike anything that is not verified for industrial use like that RS485 to USB converter.

We bought 2 IoT2040s on behalf of our client and we are quite disappointed that we have to tell them to disregard one of them. I hope this issue will get resolved ASAP. Otherwise not only we have to take the gateway back, we also have to buy another equipment out of our own money and it hurts our reputation as a system integrator. 

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Split from Problems with the RS-485 serial - Modbus RTU.