Modicon Momentum


Thread Starter

Jay Kirsch


I am using three Modicon Momentums (171 CCS 760 00 ) with the IEC executive (2.2) and Modbus-Plus options modules to control a small plant. About once every other day, one of the Momentums crashes, the CPU is inaccessible until power is cycled, then the program is "not equal".

If anyone else is having similar problems, I'd like to know, including your hardware configuration. Of course a solution would be even better, but Modicon doesn't have yet that I know of.


Jay Kirsch
[email protected] <mailto:[email protected]>

Humberto Nunes

Hello Jay Kirsch:

Your problems sounds the same as what had been happening here at Alcan. I spoke with a couple of people who were working on the momentum’s, and they were also crashing randomly.

Apparently the problem was the Modbus Plus Communications cable. The Modbus Plus Cable was not supplied from Modicon but from a 3rd party supplier. Once the Modbus Plus cable was replaced with Modicon cable, the crashes stopped.

I hope this is helpful.

Best Regards,

Humberto Nunes
[email protected]

Steve Banack


I agree with Humberto, if you are using a 3rd party MB+ cable, chances are you will come up with errors.

The MB+ protocol is just like RS-485 in that you require proper resistance at the end of the line. Schneider takes care of this in their cables.

If the schneider cables are not to your liking (i.e. too short) I recommend using their inline connectors (ASMBKT 85) and using their terminators at the end (ASMBKT 0185). You can use Beldon #9841x cable to connect.

I hope that this helps you.


Steve Banack, CET

Customer Central, Schneider Automation

Mr. Kirsh,
Thank you for posting this issue. Our technical support organization is working with you to provide a workaround for this problem. We have recently observed this problem with other customers in which the Momentum M1 processor crashes and loses memory. It does not appear to be related to the presence of a ModBus + cable. The problem is intermittent, and has been hard to replicate reliably. We understand the seriousness of the problem and consequently this has top priority in our Engineering organization. Tests are in process in our plant as well as at one customer location. We are hopeful of a speedy resolution. Your support case is still active and a resolution will be provided through our organization.

Schneider Automation
Customer Central
Your tech support people have been very helpful thusfar in helping to fix this problem. I was hoping someone on the list here might be able to add to the data we have and narrow the problem down to firmware, the CPU, or the Modbus-Plus options module.

I have a lot of Momentums running just fine on other projects. With the same CPU, the combination of Modbus-Plus and a 984 exec does not cause this problem, nor does the combination of Interbus-S and the IEC exec (2.1).

Jay Kirsch
You may also want to check the MB+ chip used. Below is a issue we ran into that the local distributor had not heard of from Modicon.

We called Modicon support and after some deliberation and a couple of phone calls back and forth, we were informed the failing units had all been built in the 37th week of 1999. At that time Modicon utilized a KSLI processor chip which has since been determined to be faulty. Since that time they are using a INTEL chip which works. If you come across this problem where the node MB+ communications dies, pull the board out of the hat and look for the processor chip.If it says KSLI, contact Modicon for warranty replacement.

J.C. Teixidó

I received this throught a Schneider Dealer.

Have been detected problems with CPUs, when there is a CPU with a option module
(i.e. Modbus+ adapter)and use de I/O bus.

the afected units are 171CCS76000 M1 processor with s/n from 310032xxxxx to
310152xxxxx.Dates from 08/06/00 to 12/01/01.

New units (without problems) are s/n greater than
310210xxxxx or SV: equal or greater then 2.06 or
PV equal o greater than 02.