RSLogix5000: Retaining tag values when downloading

Hello, I am tasked to update a CompactLogix PLC program on a live system. The updates I need to make involve changing a user-defined data structure (UDT) within the program.

This apparently can't be done online, and requires me to edit the program offline, then re-download it to the controller.


The controller has a lot of counters, configuration settings, etc which should not be modified.



How can I ensure the tag values won't be changed when downloading the new program? I can't see any way to download only the program without downloading the tag values also.


The only way I can see to do this is to:
1. Upload the current program while online. (copies all tag values as they currently are)

2. Go offline
3. Modify the UDT
4. Download the program to the controller
At this point all tag values will be copied from what they were in step 1.


Is there a better way to achieve this without needing to download tag values and set them back to whatever they were in step #1? For example, if a counter continues to run after I upload in step #1, then when I download in step 4, the counter will be reset back to the previous value, thus losing any change since step #1.


Thanks for any pointers.


EDIT: I think this thread basically answers the question: http://www.plctalk.net/qanda/showthread.php?t=26302

You outlined exactly what you need to do for the best results. One other recommendation I would make is to stop the system if possible to an idle state and advise all operators to leave it alone while you make the changes. This will ensure all data at the current state is retained.

One other thing I like to do is after an upload, do a save as and create a pre edits file that is the image before making any changes. That way if you have to punt back you can do so easily.

Thanks @_Dock_. I now understand that program and tag memory are not separate in the CLX controllers; thus a partial download of only the program is not possible. This expectation comes from my familiarity with the CLICK series of mini PLCs which allow the program to be transferred without interfering with data memory.

_Dock_ said:

You outlined exactly what you need to do for the best results. One other recommendation I would make is to stop the system if possible to an idle state and advise all operators to leave it alone while you make the changes. This will ensure all data at the current state is retained.

Click to expand...

Got it. To confirm, is there any way to edit a UDT while online?

_Dock_ said:

One other thing I like to do is after an upload, do a save as and create a pre edits file that is the image before making any changes. That way if you have to punt back you can do so easily.

Click to expand...

ryangriggs said:

Is there a better way to achieve this without needing to download tag values and set them back to whatever they were in step #1? For example, if a counter continues to run after I upload in step #1, then when I download in step 4, the counter will be reset back to the previous value, thus losing any change since step #1.

Click to expand...

There is not a good way to do it that I'm aware of.

Here's one alternative. While you cannot change an (in-use) UDT, you can create a new one. Export your UDT, make changes in an offline file, then go online and import the changed version under a different name. While still online, create tags of the new UDT type corresponding to any you have of the old type, then do online edits to change all references in the program to the new tags. You can then delete the original tags and UDT and rename the new ones to match the original if desired.

Whether this is in any way 'better' is debatable at best. It's more work proportional to the number of tag references in the logic that need to be changed, and there's potential issues if they are in different programs.

ryangriggs said:

Got it. To confirm, is there any way to edit a UDT while online?

Click to expand...

I believe you can change a UDT if there are no existing tags using it.

There is a tag upload/download tool for the CLX family. Since a download will require going to program mode anyway, you could go to program mode, upload all the tags, download the program, download the tags you just uploaded and continue.

I have never actually used this thing so I don't know how well it works or if it even works at all. Also, if it works at all I don't know how resilient it is. For example, if your new program deletes some tags that were part of the original upload, will the tool just skip them and note this or will it lock up? I don't know.

Keith

kamenges said:

There is a tag upload/download tool for the CLX family. Since a download will require going to program mode anyway, you could go to program mode, upload all the tags, download the program, download the tags you just uploaded and continue.

I have never actually used this thing so I don't know how well it works or if it even works at all. Also, if it works at all I don't know how resilient it is. For example, if your new program deletes some tags that were part of the original upload, will the tool just skip them and note this or will it lock up? I don't know.

Keith

Click to expand...

I haven’t used it a lot either... I’ve always believed that the tool was more for saving tag snapshots over a course of time, or transferring tag values from one system to another. Seems overkill for this scenario, especially if he can take the line down for just a few minutes. If he had a several week edit with multiple instances of changed values during that time then that is where the tag upload/download tool would be an advantage.

Thanks everyone for the advice!

V33 released this year will permit editing existing and in use UDTs online! Great feature advertising, however elements cannot be added/removed, only renamed.

When editing with existing data one of the habits I follow is spot-checking a couple elements to verify that the data did not change unexpectedly after the work is done. There have been a couple issues in the past where moving elements and renaming caused the data to move unexpectedly if completed without frequently pressing the Apply button.