Beckhoff TC3 linked variable not updating

deisengard

Member
Join Date
Apr 2017
Location
Indiana
Posts
2
Background
  • Upgraded from an older TwinCAT 3 build (in the VS2010 shell) to the current one (in the VS2013 shell).
  • Opened project created in older environment and cleared a few visualization-related issues. Project builds fine.
  • Unfortunately, the CX9020 PLC had to be reset (long story), which I did by renaming the Documents and Settings folder on the SD card.
  • Activated the newly built configuration successfully.
  • The only change to the project from before any of the above was an additional link between a new global output variable in the existing PLC task and an EL2124 digital output unit, as well as an additional line of code in the MAIN POU that sets the value of the new output variable.

Problem
After activating the updated configuration, another, separate link seems to have stopped working. It is a link between an input from an EL6695 EtherCAT bridge and a global input variable in the PLC task. While logged in to the PLC, when the value of the input changes on the EL6695, the corresponding linked variable in the PLC does not reflect the changed value.

All of my PLC inputs and outputs are defined using %I* and %Q*. I have made this sort of change before without any issue, so I'm confused. Does anyone have any suggestions on how to diagnose the problem with the link not updating? It's very possible I'm missing some obvious step since it's been a while since I made changes.

Thanks in advance.
 
Sorry for seeing your question so late.

I noticed "an additional link between a new global output variable".
One is allowed to link only one PLC variable linked to an output channel. Otherwise, they would fight over what the output should be. One can share an input channel with multiple PLC variables.

A few things you can try (from memory, I don't have a PLC in front of me, so "kind of like"):
"Clear All" and "No" to "keep associations". That will force resetting the auto-mapping of %I* and %Q*.

Under "System" (formerly System Manager utility in TC2), see if the EL6695 outputs change under the "I/O" tree. That tells you if the module (terminal) readings are updating. In Config mode, set "Free Run" so SM polls the module. If it doesn't update there, the problem is upstream of the PLC variable linking. If it works there, view the PLC variable value under your PLC Project's "Instance". I recall for that to update, the PLC engine must be in Run mode and the PLC code must be Running (log-in, PLC tab - Run). Also, insure the value is not being Forced. Some of that is a bit confusing, but I usually see things updating after clicking around.

Finally, something at a high level which can prove confusing is if you set the Embedded Write filters (Beckhoff utility or low-level Windows cmd), but I think that is just for embedded Windows and not a CX9020 (ARM CPU). That makes the PC boot-up as it was just before the Write filter was set, which is intended to set a carved-in-stone baseline configuration.

Please let us know the outcome.
 

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