Reading Tag description

Mikel Ayani

unread,

Apr 24, 2025, 11:08:36 AMApr 24

to libplctag

Hi, does anyone tried to read the extended properties of tags like the Description?

I am working on a project and I need to get the Description of each bit on a DINT, like the HMI does.

Thanks!

Kyle

unread,

Apr 24, 2025, 11:11:45 AMApr 24

to libplctag

There is an open issue on it #358. I have not been able to test but the changes I made apparently do not work. I am away from my lab for a while but I will be returning to this in the future. If you have a way to use Wireshark to capture what the HMI does to find that data, it would be useful.

Best,

Kyle

Mikel Ayani

unread,

Apr 24, 2025, 11:32:34 PMApr 24

to libplctag

Thanks Kyle!

No problem, I am quite in a hurry to solve this and I wanted to know the status of the issue.

I have already done some tests with wireshark and I was able to get the telegram where Studio5000 writes a new description value in the PLC. I need to get the one that reads the description and the petition.

I am doing tests with pycomm3 library and sending generic messages too.

I will keep you updated if I solve it.

Kyle

unread,

May 3, 2025, 10:56:59 AMMay 3

to libplctag

I am very interested if you figure it out! I would love to add that. I suspect that Studio5000 is doing some translation of the names to CIP attributes or something similar.

Best,

Kyle

Mikel Ayani

unread,

May 5, 2025, 9:50:00 AMMay 5

to libplctag

I did many tests and ended up using wireshark and chatpgt to figure out what was going on.

Even if I tried to send identical requests with pycomm3 CIPDriver replicating what Studio5000 sends, I ended up getting "Permission denied" messages from the PLC.

Most likely, there is something going on, undocumented, between Studio5000 and the PLC when the session is started.

The messages to modify or read descriptions include some payload that is dependent on the session and probably some "key" exchanged during the session start.

That part changes in every call so even sending an exact copy of the message does not work.

So I do not believe the descriptions can be gathered easily.

And reverse engineering the session start could even be ilegal...

Kyle

unread,

May 10, 2025, 9:32:50 PMMay 10

to libplctag

The description, min, max etc. are in a "protected" space in the PLC. I got confirmation of that. I do not know how to get into that protected space. It may have something to do with all the extra Forward Opens that Logix Studio does when it opens a project against the PLC.