Counters And Loopback Diagnostics; Debugging Tool And Documents - ABB RS485 Installation And Startup Manual

Writings in the controller memory through Modbus are restricted to a limited range
applied on that data. An exception error is sent in case of a writing exceeding the allowed
limited range of a data.

7.7 Counters and Loopback diagnostics

Modbus offers some interesting functions to help the user to locate errors:
Fetch comm event counter (function 11) to catch successful messages.
Fetch comm event log (function 12) to look at the history of errors.
Diagnostics function and subfunctions (function 8)
Loopback diagnostics (subfunction 0) returns a response identical to the query
Restart communication (subfunction 1)
Force Listen only mode (subfunction 4)
Read various diagnostic counters

7.8 Debugging tool and documents

The user can find much application on the internet to scan Modbus devices and test
communication.
Look in the documentation of the controller and the corresponding Modbus data table for
appropriate information.
Look in the Modbus protocol for more information on Modbus.
RS485  Troubleshooting - 19