Re: [foxboro] FBM231 modbus with siemens
- From: "Wilson, Brad" <brad.wilson@xxxxxxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Mon, 22 Oct 2007 19:03:53 -0400
As I'm sure you know, the FDSI no longer uses a Modbus transaction
definition like the old FDSCAN blocks (with DI30) and the device config
file (with FBM224). The Modbus driver knows that a DCI read block (BIN,
PAKIN) to any address in the 00001-09999 range will be a function code
01, so there is no need to define it as such. Likewise for reads or
writes to any of the Modbus memory blocks (0x,1x,3x,4x). In my
particular case, the behavior I observed was that with the ECB201 built
and no DCI blocks built, everything was healthy, I got Tx/Rx lights
blinking and the SysMon was happy. As soon as I built a single DCI
block, the PLC would shutdown. If I deleted the DCI and rebooted the
PLC, it was happy again. The gurus in TAC did some forensics and found
that the FDSI was formatting the initial packet with a read to address
40001 in the header, even though that was not in my DCI block. As they
explain it, normal PLC behavor would be to either reply with the
contents of 40001 (if configured) or reply with an exception code (if
not configured). Either response would tell the FDSI that the PLC is
alive and the DCI would then proceed to read its data. With the Siemens
S7 though, it was not responding with an exception; it was shutting
down. I don't know if this is normal with Siemens, or just with the
interface written for this particular PLC. At any rate, TAC explained
that if the heartbeat is enabled (function code 08), the FDSI uses that
as a health indicator instead of trying to read address 40001. I'm be
curious to hear of other experiences with Modbus FDSI.
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 Corey R Clingo
Sent: Monday, October 22, 2007 6:27 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] FBM231 modbus with siemens
Is there a block configured to read address 40001 in this application?
If not, this certainly sounds like an overreaction on the part of the =
Siemens PLC, but the FBM231 is not completely blameless; it should not
be =
polling for unconfigured data.
Corey Clingo
BASF Corporation
"Wilson, Brad" <brad.wilson@xxxxxxxxxxxxxxxx> =
Sent by: foxboro-bounce@xxxxxxxxxxxxx
10/19/2007 09:03 AM
Please respond to
foxboro@xxxxxxxxxxxxx
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Re: [foxboro] FBM231 modbus with siemens
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
=
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