Hello professionals,

we are planing to put the modbus connectivity to our product.
In the technical resources is written about diagnostic-functions....
are these functions necessary to drive a modbus slave? Are there any functions which are necessary?

thanks for your help
Kind regards
Vincenzo Nuzzi

 

Diagnostic functions aren't necessary to drive slave but it provides a series of tests for checking the communication system between the master and slave, or for checking various internal error conditions within the slave. function 08 with 00 02 return diagnostic register subfunction is useful for maintenance.

 

I'm not sure what you mean by diagnostics.

The Modbus specifications define specific errors. The Modbus Conformance Spec specifies numerous tests for error handling.

The Modbus user community expects the defined error handling.

The Modbus specifications are available for download from Modbus IDA on an associated web site.
http://www.modbus.org/specs.php

Here's a couple statements from the various Modbus standards regarding errors.

-MODBUS APPLICATION PROTOCOL SPECIFICATION, V1.1b, page 4
If an error related to the MODBUS function requested occurs, the field contains an exception code that the server application can use to determine the next action to be taken.

-MODBUS MESSAGING ON TCP/IP IMPLEMENTATION GUIDE, V1.0b
MODBUS Response PDU
The function code must be verified and the MODBUS response format analyzed according to the MODBUS Application Protocol:
<snip>
If the function code is different from the one used in the request (=non expected function code), or if the format of the response is incorrect, then an error is signaled to the user application using a Negative Confirmation.

-Conformance Test Specification for Modbus TCP, Version 3.0
1. Summary
<snip>
Additionally it will test for message error handling and message format error handling.

The document lists numerous tests for error handling.