4.4.1 Extended Diagnostic Messages for RedCom
The Redundancy Extensions to the standard V1 protocol allow the two channels to communicate
between themselves to establish correct operation of the highway if there is a failure, both the Simple
and RedCom versions of the card do this. In addition to these, there are extra Extended Diagnostic
messages that are reported to the PLC as part of the RedCom system that the Dual RedCom card
reports. Not all PLCs are RedCom compliant, so some are unable to understand these messages and,
as a consequence, will mark the device as having an Error. If this is the case, either reconfigure the
Profibus card to be ‘Simple’ or disable the PLC’s diagnostics package that is looking at the extended
diagnostics.
A RedCom Dual Channel card can be altered to a Simple Dual Channel card, or vice versa, by
entering the appropriate value in parameter 15 in the GSD file.
The extended diagnostics is contained in 3 bytes in the diagnostic message and is reported by the
Primary slave only:
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