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Verfügbare Sprachen
Irrespective of the function used, the register address 30001 or 40001 would be addressed in the transmitted mes-
sage as register 0, 30002 or 40002 as register 1, 30010 or 40010 as register 9 and so on.
In the Modbus communications all these register addresses are not active and don't contain valid information. A read
or write to an unused register address will produce an exception error.
7.6. Check the data access level and the limited range of data
To ensure that a write message to a Modbus address will produce a normal response, check that the data value and
access level is valid.
Writings in the controller memory though Modbus are restricted to the setting of some access levels which need to be
set. Look at:
– SET MODE
– LOCKING SWITCH
– BANK SETTINGS
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.
8. Appendices
A1 List of abbreviations
ASCII
Baud rate
STATUS
Approved
American Standard Code for Information Interchange
Unit for measuring transmission speed in bits/s;
SECURITY LEVEL
Public
DOCUMENT ID
9AKK107045A9895
RS 48 5 A DAPTE R
REV.
LANG.
PAGE
E
en
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