Hi Florian, If you have a look at http://en.wikipedia.org/wiki/Modbus you can see the difference in frame format. Basically there are three variants:
Modbus RTU - modbus over serial interface, includes using CRC calculations for error checking Modbus RTU over TCP - sends the RTU over a TCP/IP connection to a remote serial interface. Still uses RTU frame format including CRC calculations Modbus/TCP - has a slightly different frame format and doesn't use CRC calculations. Unfortunately the last two variants are often confused :-) libmodbus appears to currently support Modbus RTU and Modbus/TCP. Regards, Matt > Hi Matt, > > On Fri, Jan 07, 2011 at 10:33:34PM +1030, Matt Baker wrote: >> Unfortunately though I discovered that the device I am using to do the >> Modbus conversion supports Modbus/TCP for interfaces connected >> directly, but provides a Modbus RTU over TCP for other external Modbus >> serial devices. > > I thought that's what Modbus/TCP was, the Modbus protocol encapsulated > in a TCP stream rather than written to a serial interface. How is this > "RTU over TCP" thing different? Is there an additional protocol layer? > >> Before I start going into this too far I was wondering if you had any >> thoughts on how difficult it would be to modify collectd to do this? > > I'd actually implement this for "libmodbus" first, then adapt collectd / > the Modbus plugin if necessary. Author and maintainer of libmodbus is > Stéphane Raimbault who is very likely a much better help with anything > Modbus related than I am ;) > > Best regards, > —octo > -- > Florian octo Forster > Hacker in training > GnuPG: 0x0C705A15 > http://octo.it/ _______________________________________________ collectd mailing list [email protected] http://mailman.verplant.org/listinfo/collectd
