Wireshark-bugs: [Wireshark-bugs] [Bug 7902] Improved Dissection of Modbus/TCP messages and added
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From: bugzilla-daemon@xxxxxxxxxxxxx
Date: Fri, 26 Oct 2012 08:18:01 -0700 (PDT)
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=7902

--- Comment #32 from Chris Bontje <cbontje@xxxxxxxxx> 2012-10-26 08:18:00 PDT ---
(In reply to comment #31)
> Comment on attachment 9412 [details]
> Modbus RTU (Serial) for use with User_DLT Dissector ("Modicon Float" data
> types)
> 
> Chris,
> 
> The CRCs for these packets don't seem to match the CRC algorithm for Modbus
> (per Modbus.org).  Is that intentional?

Glad to see part of the patch made it in!  Agreed, it was getting large and a
little difficult to manage!

As far as the CRCs go, I assume you speaking of the CRCs for the Modbus RTU
packets?  They all checked out as valid on my test equipment/software (from a
variety of manufacturers) and they are reported valid by the CRC-16 "Modbus"
algorithm as found on this web site (albeit, displayed in reverse byte order):
http://www.lammertbies.nl/comm/info/crc-calculation.html

Chris

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