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Old November 14th, 2017, 10:32 AM   #1

JohnCalderwood is offline
Join Date: Feb 2014
Location: Stirling
Posts: 647
1756-L55 Clearing Memory

Some information for the folks on here.

We had a 1756-L55 clear its memory whilst running. The guys managed to power it down and reload an old backup to get it going.

The PLC was checked out by Rockwell - here is their response :

The 1756-L55 debug.out diagnostic file has been analyzed, here is the report:
The Logix controller in your system experienced a Major Non-Recoverable Fault (MNRF). This specific MNRF was caused by a soft memory error. After careful review of the data provided to Rockwell Automation, it has been determined that this occurrence of a soft memory error was not caused by a firmware or hardware anomaly. The controller is working as expected. Furthermore, we have not seen soft memory errors caused by power, grounding, or electrical noise.

Logix controllers run a continuous series of background diagnostic tests including monitoring for soft memory errors. Diagnostic tests are performed to ensure the safe operation of the controller. If a soft memory error is encountered, a Major Non-Recoverable Fault (MNRF) will be declared by the controller. A MNRF is a controlled action taken by the controller when it is determined that the controller could no longer continue safe operation. When a Logix controller determines that a MNRF is the right course of action, the controller is designed to fault, taking it out of run mode, logging diagnostic data, and then invalidating and deleting the controllerís memory. This action requires an application program reload to guarantee the controller has a valid program to continue safe operation.
Never seen this one before, but we have a few ageing L55 PLCs, already changed one previously due to memory leak from InTouch 2014R2.
One to watch with the older processors I think....
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