Re: [foxboro] FBM231 modbus with siemens
- From: Stephen Bettesworth <stephenb@xxxxxxxxxxxx>
- To: foxboro@xxxxxxxxxxxxx
- Date: Fri, 19 Oct 2007 22:08:15 +1300
Patrick,
What Siemens device are you trying to communicate with? The S5 CPs can
be difficult to set up, the S7 gear is very easy. We implemented a
Modbus link to an S7 and it worked fine - after a little bit of
fiddling. If its an S7 (possibly S5 as well) then there is an extra
complication - the PLC code needs to cover all the various combinations
of reads and writes. This is very typically Siemens, enormous
flexibility and plenty of rope to hang yourself.
The actual function codes used by the FBM231 will be important, no doubt
the protocol sniffer will display them. The codes are important because
some Siemens CPs don't support all the Modbus function codes. It's
common to see only register read/writes being used in Siemens interfaces.
A scan time of 0.5 seconds sounds fast, is that the time interval
between successive polls to the PLC? What happens when you slow the
polling down to say once a second?
Rgds
Steve
FoxPat wrote:
> Dear list,
>
>
> We're having some problems with a new modbus link.
>
>
>
> FBM231, modbus driver version 1.1, scan-rate 0.5 seconds.
>
>
>
> Reading coils and registers is no problem.
>
>
>
> Writing coils works but after a certain amount of writes (just toggle of 1
> BOUT) the complete link starts to fail intermittently (works for a few
> seconds and then all smurfed for a few seconds, works again for a few
> seconds, smurfs .. Etc).
>
>
>
> Only a reset of the Siemens communication card (pull-push, there's no reset
> button) solves the problem, but after several write attempts fails again.
>
>
>
>
>
> Installed all the DCI IIN blocks for FBM port and device counters (as
> described in the manual) but these don't help me much other then indicate
> there are no CRC or framing errors. Scan time is only about 100 mSec.
>
>
>
> I hope to install a modbus analyser tomorrow to see what is actually
> happening.
>
>
>
> Anybody had similar problems?
>
> Any suggestions ?
>
>
>
>
>
> Kind regards,
>
>
>
> Patrick Martens
>
> Total Refinery Nederlands. N.V.
>
>
>
>
>
>
>
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