I would like to learn Modbus RTU in order to connect an inverter to a pc for monitoring the status of the inverter.
I have done a bit of reading about modbus, but I am unable to fully understand its capabilities until I can "play", make mistakes, and learn from my mistakes.
I am using Simply Modbus to send the machine request to the inverter (E500-2S0022). I am using a USB to serial converter (rs-485). I have triple checked my software settings and the settings in the inverter. I have sent sample requests from the owners manual (01 03 D0 00 00 02 FC CB), but I do not receive a response from the slave.
I am not sure where to start with my troubleshooting.
If you do not receive a response from the slave at all you should focus on the RS485 connection and/or communication settings. Verify baud rate, data bits, stop bits,... are correct. Is the Modbus address in the VFD configured correctly? Try switching that A and B wires.
If the slave is addressed correctly it will always respond to a request. In case of an error in the request the slave responds with an error code.