duff121:
For now I'd like to read one Modbus register. When the Arduino is connected to PC via USB cable and I choose in QModbus Serial Port of Arduino it receives correct data from the selected register without any problems (screen nr 1).
After I disconnect the USB cable, try to connect to Arduino via Serial Port of my USB FTDI RS485 converter, send 03 Modbus function read request I'm getting the CRC error 'Slave threw exception "Invalid CRC" or function not implemented" (screen nr 2)
Hi , I have the same problem 
Do you solve it ?