COMM_ERR() usage in FactoryTalk View

I have a Global Object with several parameters. One parameter can be left empty (not assigned).

I'm trying to control Visibility of a button in a pop-up based on whether or not the parameter passed to it is assigned:

COMM_ERR({#2}), result makes it invisible.

The idea that if parameter is assigned, the button is there; if not - there is no button.

It works,.. but only one time, on the first display of the pop-up! If I close it and open again, the script doesn't do anything and the button remains visible. And it doesn't work again until I save the pop-up display offline and open "brand new one". I don't cache the pop-up, and I tried flushing cache anyways - no difference...

Has anybody used the COMM_ERR function this way?

nevermind

Nevermind, I read the small print and discovered that it works only for HMI tags. For PLC tags, obviously, the behaviour is unpredictable...

2023 update

Hi.

In the decade since this post, it seems that the behaviour for this function has either intentionally changed, or the behaviour described above was due to an error that has since been fixed.

I have a sensor connected as a digital input to my PLC that I want to display on a popup when you click on a roller conveyor. The conveyor is a global object, and the tag for the sensor is Global Object Parameter #3.

As a touch animation, I open the popup using Press action "Display Popup_[Censored_Name_Here] /T{#1},{#2},{#3},{#4},{#5},{#6} /CC", retaining #3 as the sensor tag for the popup as well.

On the popup, I have a box that changes colour based on the boolean value of #3, and the box is hidden using the visibility animation, with the expression "NOT comm_err( #3 )", expression true state: visible.

When the Global Object Parameter #3 is left blank, the box is correctly hidden. If connected to a tag, the box shows up on the popup as intended. I hope this information can be of use to future users.