RSLogix5000 Add-on instructions: how to remove required InOut parameter?

In RSLogix5000 I am attempting to create an add-on instruction called "SWAP" which simply swaps the values of two integer tags.


Here is what the instruction looks like in Ladder:





As you can see, the first input is called "SWAP" and requires a tag of type "SWAP" to be created and attached. I can't understand why this parameter exists, and I can't figure out how to get rid of this. It's not present in the Parameter list. It seems messy and confusing to be required to create a separate tag every time I use the instruction, since it's only interacting with other tags to swap their values. This is not necessary on any built-in instructions, so why is it necessary on add-on instructions? Or, if it's not necessary, can you please help me understand out how to remove it?




I reviewed the Rockwell manual for add-on instructions, but I can't find anything that references this parameter or how to remove it.



Enlightenment would be greatly appreciated.



Here is the parameter config screen:


Here's the instruction's logic:

Most Instructions require a tag for them to be able store their parameter data and their status. When you create a timer, you must have a timer tag to go with it. When you create a counter, you have to create a counter tag. Likewise, when you create an AOI, each instance will require a unique tag be assigned to it. Your SWAP has an EnableIn and an EnableOut. Those bool tags must exist somewhere. Likewise your First and Second will be stored here also.

OG

ryangriggs said:

As you can see, the first input is called "SWAP" and requires a tag of type "SWAP" to be created and attached. I can't understand why this parameter exists, and I can't figure out how to get rid of this. It's not present in the Parameter list. It seems messy and confusing to be required to create a separate tag every time I use the instruction, since it's only interacting with other tags to swap their values. This is not necessary on any built-in instructions, so why is it necessary on add-on instructions? Or, if it's not necessary, can you please help me understand out how to remove it?

Click to expand...

Where do you think the 'EnableIn' bit you are using resides in memory? Answer: It's part of the tag you create. The AOI-generated data type assigns memory for EnableIn, EnableOut, and any input or output (but not InOut) data the instruction will use. Built-in instructions likely do have the same or equivalent memory usage, it's just not always exposed to the user.

In your case I suspect you could re-use the same tag for all your instructions without issue, especially given how minimal your AOI is.

EDIT:

Operaghost said:

Likewise your First and Second will be stored here also.

Click to expand...

I am reasonably confident this is incorrect -- InOut tags are passed by reference, not value, so First and Second will look at the external tags provided and will not have any internal storage for them.

Thanks, that makes sense. Not well explained in the Rockewell docs. You cleared it up.

plvlce said:

...I am reasonably confident this is incorrect -- InOut tags are passed by reference, not value, so First and Second will look at the external tags provided and will not have any internal storage for them.

Click to expand...

Correct. I had not noticed they were In/Out. But I think our point was made and the OP understood.

OG

FWIW, if your calls to the instruction reside in the same task, you need only to create one instance.