Why can’t I access my AOI local tags from my HMI?

A client contacted me this week with a problem. He couldn't get his HMI to communicate to his ControlLogix AOI's local tags.

However, what really seemed weird was that Rockwell HMI projects could do just this. So the question became, what trick was the factory using to make this possible?

I was fairly confident that referencing AOI local tags was do-able, but I thought I remembered there was some setting somewhere to enable it.

After hunting around in the software for awhile, I found the AOI Parameters and Local Tags screen did indeed have some advanced columns that were not displayed by default.

And the column and setting that I was confident was the culprit, external access, defaulted to off.

I selected it so it would be displayed, and found was the Rockwell example had the local tags set to “read/write,” while the clients had defaulted to “none.”

At this point it was as simple as changing the external access property from “none” to “Read/Write” and the HMI was now able to access the AOI's local tags.

I hope you've found this article about accessing AOI local tags helpful.

If you have a comment or question, please feel free to share it with us by clicking on the “post a comment or question” link below.

Sincerely,

Shawn Tierney
Automation Instructor and Blogger

Have a question? Join my community of automation professionals and take part in the discussion! You'll also find my PLC, HMI, and SCADA courses at TheAutomationSchool.com.

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Shawn Tierney

Shawn began programming as a pre-teen in the early 80's, and after earning a degree in Electronics he worked as an Automation Specialist for 25 years. In 1999 Shawn launched his first website which was the pre-cursor to TheAutomationBlog.com which he launched in 2013. Today Shawn continues to publish and edit content for The Automation Blog while also teaching PLC, HMI, and SCADA courses at TheAutomationSchool.com.

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