21.05.2016, 19:34
First rule when working with modbus devices - take a usb to rs485 converter (possibly isolated) and check addresses with modbus tester on laptop. Bus sniffing is also something worth learning, same as reading modbus without software decoder.
Never take the documentation or the tech's word for granted - until the device responds to you via your laptop. I had situations when the documentation and the field tech both say'd the same, but in the end I made the changes in the 3rd party device SW to made it speak modbus.
Address 4x0793 is modbus function 3 (read holding register). Are you sure it's configured correctly in LM? It can be confusing when the address is 4x for function 3 and 3x for function 4.
Never take the documentation or the tech's word for granted - until the device responds to you via your laptop. I had situations when the documentation and the field tech both say'd the same, but in the end I made the changes in the 3rd party device SW to made it speak modbus.
Address 4x0793 is modbus function 3 (read holding register). Are you sure it's configured correctly in LM? It can be confusing when the address is 4x for function 3 and 3x for function 4.