USB - RS485 Converter - FIT0737

Good afternoon,

I'm writing in this module because I recently bought a USB to RS485 converter to read from an IMD via ModbusRTU.

I know that the USB device in question uses the CH340 driver, which is pre-installed by default on Linux.

I am manually configuring the message sending, following the example provided in the IMD.

So, I send:

Slave ID | Function Code | Data (Registers to read) | CRC

However, even though the TX light turns on, the RX does not.

After some research, I tried adding a start bit "AA" and a stop bit "55". The result was the same.

Previously, I had bought a device that used a CH340 chip, but in that case, it was a USB to CAN converter. It initially required sending a series of commands for configuration.

But for MODBUS RTU, I think this should not be necessary, as sending the packet should be sufficient.

I have confirmed that all parameters match the examples in the datasheet, and they do.

My question is: is there any initial configuration needed for the CH340 chip? Do I need to send any specific bit to activate the chip? Or could the error be with the IMD?