Writing a tag value to all UDT instances for memory tag

Ignition
1

I have a UDT with a memory string tag. When I update the value for that string, I would expect all instances of the UDT to have that same value for that. But, it looks like all the instances still have a nothing in for that tag value. Any idea why?

2

I think the problem I was having here is if you already have instances of a UDT that you want to change a memory tag value for, changing the value inside the UDT definition doesn’t retroactively change the tag values for the instances.

What I did discover is that any new tags you create under that instance will have that value for the memory tag inside of the definition.

3

This is intended behavior for a memory tag. Its purpose is to remember what is written to it. If you need a constant tag defined by the UDT, use an expression tag with a constant expression. Changing that in your UDT definition will change all instances.

4

thank you