Re: [foxboro] FBM231 modbus with siemens
- From: "Wilson, Brad" <brad.wilson@xxxxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Fri, 19 Oct 2007 10:03:00 -0400
In trying to set up a FBM231 with a Siemens S7, I discovered that the
FBM231 tries to establish a comm link with the PLC before sending a
request. In the absence of a heartbeat, it sends a read request to
address 40001 (the first entry of the holding register. If the Siemsns
receives a request to an undefined address, it shuts down the comm port.
So, if 40001 is undefined then the PLC immediately goes off-line and can
only be restored by cycling power. There may be other "odd" behaviour
associated with Siemens too. Be sure that heartbeat (FC8) is turned on.
It would seem that standard modbus is not always so "standard".
Brad Wilson
brad.wilson@xxxxxxxxxxxxxxxx
Invensys Systems, Inc
1090 King Georges Post Rd, Suite 204
Edison, NJ 08837
732-874-0087
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Gonzalo Diaz
Sent: Friday, October 19, 2007 8:53 AM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] FBM231 modbus with siemens
Try the following things:
- to use another modbus slave (such as an analyzer) and see if the =3D
problem
persists.
- use a modbus simulator to read and write coils and registers to the
siemens plc...as said in another post, the siemens plc uses custom =3D
blocks
and functios installed on the cp's to perform modbus comunications. =3D
Since it
is not a standar for siemens, there might be some limitations regarding
modbus functios
- to read and write only one register at a time. If this works, then
increase the data being requested by little increments.
- take a look on how many bytes are you sending and requesting, try to =3D
limit
the byte quantity to no more than 100 bytes
- try to establish a poll frequency for no less than a second, i guess =3D
500
msec is to high (it depends on the physicall link, indeed)
if you dont have a modbus simulator i can send you one.
good luck
Gonzalo Diaz
Mantenimiento Planta LPG
Servicios Buproneu S.A. (Capex S.A.)
Yacimiento "Agua del Caj=3DF3n"
-----Mensaje original-----
De: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx] =3D
En
nombre de FoxPat
Enviado el: Jueves, 18 de Octubre de 2007 14:14
Para: foxboro@xxxxxxxxxxxxx
Asunto: [foxboro] FBM231 modbus with siemens
Dear list,
=3D20
We're having some problems with a new modbus link.
=3D20
FBM231, modbus driver version 1.1, scan-rate 0.5 seconds.
=3D20
Reading coils and registers is no problem.
=3D20
Writing coils works but after a certain amount of writes (just toggle of
=3D
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).
=3D20
Only a reset of the Siemens communication card (pull-push, there's no =3D
reset
button) solves the problem, but after several write attempts fails =3D
again.
=3D20
=3D20
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 =3D
indicate
there are no CRC or framing errors. Scan time is only about 100 mSec.=3D20
=3D20
I hope to install a modbus analyser tomorrow to see what is actually
happening.
=3D20
Anybody had similar problems?
Any suggestions ?
=3D20
=3D20
Kind regards,
=3D20
Patrick Martens
Total Refinery Nederlands. N.V.
=3D20
=3D20
=3D20
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