Re: [foxboro] Friday Afternoon modbus plus question

I have never used MB+, but every other token-passing network I've used has 
some mechanism to prevent "hogging" of the token.  Usually one station is 
designated as the "token monitor" (the one with the lowest address or 
something), and if the token is not passed within some time limit, or the 
token doesn't make the round trip (say, it gets passed to an offline 
station), the token monitor declares the token invalid and issues another 
one.  If the token round-trip time is longer than your MDSCAN period, then 
I can imagine you would have problems, but I couldn't tell you how to look 
at that on a MB+ net.

Token-passing networks are far better than, say, shared ethernet (or 
*cough* nodebus *cough*) at handling contention and high loads.  I see the 
same issues on A-B DH+ networks (also token-passing) where I have 
integrator I/O scanning overruns while all other devices on the network 
(i.e., all the ones that say A-B on them) function properly.  For that and 
other reasons I've concluded that the integrator software (at least for 
Integrator 30s) is just not very good.  Unfortunately this doesn't help 
your situation.


Now, as to why I didn't see your results listed for the Wisconsin primary, 
I haven't a clue.


Good luck,


Corey Clingo
BASF Corporation






David Johnson <drjohn@xxxxxxxxxx> 
Sent by: foxboro-bounce@xxxxxxxxxxxxx
02/15/2008 03:18 PM
Please respond to
foxboro@xxxxxxxxxxxxx


To
Foxboro@xxxxxxxxxxxxx
cc

Subject
[foxboro] Friday Afternoon modbus plus question





Hey everybody!
I've got a network with 3 modbus plus integrators and  13 modicon
plcs on one modbus plus network.  All of the integrators are having
processor overruns, most seem to be due to the physical I/O
scan.  Leading us to wonder.....

Since modbus plus is a token passing network, and everything is on
one network, are we getting token contention issues from the
Integrators themselves.  In other words if I have several MDSCANs in
each INT30, is the first MDSCAN grabbing the token and holding on to
it until it's read request is completed?  Thus screwing (the
technical term) the other gateways.  If that is the case what can we
do to improve our efficiency.  (Assume we have already phased
everything properly and are maximizing data in MDSCAN requests.)

Thanks.
David
PS ---
I'd like to thank all those that attended the Southeastern I/A Users
Group meeting.  I think it was a big success, I hope you did too.

PPS---
If you like your rock/punk  a little ragged, check out the Foxboro Hot 
Tubs....
http://www.foxborohottubs.com
That's for you John Kinsley!





 
 
_______________________________________________________________________
This mailing list is neither sponsored nor endorsed by Invensys Process
Systems (formerly The Foxboro Company). Use the info you obtain here at
your own risks. Read http://www.thecassandraproject.org/disclaimer.html
 
foxboro mailing list:             http://www.freelists.org/list/foxboro
to subscribe:         mailto:foxboro-request@xxxxxxxxxxxxx?subject=join
to unsubscribe:      mailto:foxboro-request@xxxxxxxxxxxxx?subject=leave

Other related posts: