1756-L61 dumping its program

We have a 1756-L61 that dumps its program as soon as we enable a particular MSG. Sometimes it does it immediately, sometimes not for a couple of seconds, and recently it ran for 2.5 days and then dumped it. Everything that the MSG points to on the other end is OK. Several other PLC's point off to the same location as this faulty MSG does and they run fine. We have tried removing the MSG instruction and re-inserting it. Already opened an RA Case but they seem unwilling to help. Any ideas?

Welcome to the Forum.

I've never heard of a MSG instruction causing a processor fault. Could it be that it's a coincidence, or that something that happens subsequent to the message completion that causes a fault ?

What port, what address, and what Source and Destination tags is the MSG using ?

Is this a Recoverable (blinking red LED) or an Unrecoverable (solid red LED) fault ?

If the fault is Recoverable, what is the fault code shown in the Processor status dialog ?

If the fault is Unrecoverable, have you used the Fault Dump Utility to retrieve an operating system crash log ? This information is also written onto a CF card if one is installed and you are running firmware v17 or later.

What firmware version are you running in the 1756-L61 ? Can you also post the firmware revisions of the network modules involved ?

Is this a new system, a system that's just begun to fault, or a system that has always had faults of this kind ?

Have you added or removed anything significant from the system, either in the program, electrically, or physically ?

As always Ken has the right questions, answer these and your problem will be solved.

It is possible that your hardware/firmare combo have issues, but does sound wierd that the MSG instruction is triggering it

I had an instance a couple of years back, related to a certain CPU model & firmware revision, there was a tech note on the issue, and we did get it solved, but perhaps this is a new case?

Sorry for the delay but i wanted to get with the guy who was working closely on this to make sure i had all the info. Below is the email i had sent him with your questions and his responses.


I've never heard of a MSG instruction causing a processor fault. Could it be that it's a coincidence, or that something that happens subsequent to the message completion that causes a fault ?The message goes .DN and runs, sometimes for seconds, sometimes for minutes, once for 2.5 days. But the program will run indefinitely with that message disabled.

What port, what address, and what Source and Destination tags is the MSG using ?It is a read message in a CL5k. It reads from a PLC50/80E. 1756-ENBT: IP=192.168.20.105 SN=255.255.255.0, GW=192.168.20.1. 1785: IP=192.168.15.71 SN=255.255.255.0 GW=192.168.15.1. It reads from N397:0 Len=10 (20bytes). I have tried reading it into 2 different destinations, 1. The first 20bytes of a 44byte SINT[44]. 2. A UDT of several types, totaling 44bytes.

Is this a Recoverable (blinking red LED) or an Unrecoverable (solid red LED) fault ? Unrecoverable

If the fault is Unrecoverable, have you used the Fault Dump Utility to retrieve an operating system crash log ? This information is also written onto a CF card if one is installed and you are running firmware v17 or later.I am using V16, I have submitted dump files of 2 of the crashes but RA has not responded yet. They are also unable to duplicate the crash at their facility.

What firmware version are you running in the 1756-L61 ? v16.7 Can you also post the firmware revisions of the network modules involved ? 1756-L61 = v16.7 (I flashed up to 16.24? at the request of RA but my problem got significantly worse so I flashed back down. 1756/ENBT/A = 5.1

Is this a new system, a system that's just begun to fault, or a system that has always had faults of this kind ?It ran without incident for 2 or 3 years. I was adding some more code recently and when I got to this message it faulted.

Have you added or removed anything significant from the system, either in the program, electrically, or physically ? This PLC is in a 4 slot rack with 2 modules the, L61 (self) and ENBT. It is used as a data concentrator or data router. It has no i/o. The new things are one new program and its routines and tags, and 2 UDTs.

Update: RA has finally contacted us back and are going to send us a new CPU and a flash mem card to install. We are supposed to let it crash (a MAJOR/Expensive deal on the production floor) and then swap them back out and send the faulted unit/card back to them for analysis. So this may end up getting fixed in a month or so but we would sure like to have it going before then.

Thank you for your help.
Jason