Logix Designer Structured Text help

Hi all, this is a long one, so there's a TL;DR at the bottom

I have a situation where I'm dragging data from an external database into a UDT in a Control Logix PLC. The only problem is, the only way I can get the data to come in is by arraying the UDT elements, instead of arraying the UDT itself. By which I mean, the normal way I would do it is to create a UDT as follows:

ID, DINT
Name, STRING
Speed, DINT
Temperature, REAL
...
...

and then I would create an array of this UDT, so that I have:

Recipe[0].ID
Recipe[0].Name
Recipe[0].Speed
Recipe[0].Temperature
Recipe[1].ID
Recipe[1].Name
Recipe[1].Speed
Recipe[1].Temperature
Recipe[2].ID
Recipe[2].Name
...
...
Recipe[99].Speed
Recipe[99].Temperature

But I can't do that. I have to create the UDT like this:

ID, DINT[100]
Name, STRING[100]
Speed, DINT[100]
Temperature, REAL[100]
...
...

Which means I then create a single instance of this UDT, which is populated from my DB, and looks like this:

Recipe.ID[0]
Recipe.ID[1]
...
...
Recipe.ID[99]
Recipe.Name[0]
Recipe.Name[1]
...
...
Recipe.Name[99]

Obviously this is a pain for a lot of reasons, but I can live with it for now. However, what I'd like to do is create a UDT the "proper" way, and when the operator calls for a recipe, copy the data from the relevant database fields into that one UDT for loading into the line parameters. So if they call for recipe 12, I copy Recipe.ID[12] into RecipeUDT.ID, Recipe.Name[12] into RecipeUDT.Name, and so on.

I'm fine with the concept of indirect addressing, but what I'd like to do is use structured text to iterate through each element of the array instead of having to manually code a copy for each element of the array. I'm a complete novice at ST, so I'm not sure how to approach it, but I would imagine that it would look something like:


Am I close to the mark? Is there anyone who's a more familiar with ST that can give me a nudge in the right dance floor?

Thanks!

TL;DR - from a UDT where each element is arrayed, can I copy the data from one array element into a UDT with an identical structure but with single (not arrayed) elements?

As far I know there's no method to iterate through the elements of a UDT. I think your best option is to use an index and copy each element belonging to a recipe:

You only will need to provide the correct index to load a recipe.

Damn, that's what I was afraid of. If I have to do it all manually I'll just do it in ladder for consistency - I had just hoped there might be a creative way to do it with ST.

Anyone else know any quirky tricks to make this work?

ASF said:

Damn, that's what I was afraid of. If I have to do it all manually I'll just do it in ladder for consistency - I had just hoped there might be a creative way to do it with ST.

Anyone else know any quirky tricks to make this work?

Click to expand...

I don't see why this is a hassle, create an AOI based on ST, input your DB arrays into it, and output the Recipe[x] UDT tag.

Should be all you need

Yep - but that's still doing it all manually. You've got one line for each element of the recipe, and in my example there are significantly more than the four I've thrown up there as an example.

The loop you're using is to loop through each recipe and put ALL of them into a correctly-shaped UDT - I only need to get out one at a time, but I just want to try and do it without having to have 40 lines for the 40 different parameters.

ASF said:

Yep - but that's still doing it all manually. You've got one line for each element of the recipe, and in my example there are significantly more than the four I've thrown up there as an example.

The loop you're using is to loop through each recipe and put ALL of them into a correctly-shaped UDT - I only need to get out one at a time, but I just want to try and do it without having to have 40 lines for the 40 different parameters.

Click to expand...

Ok I see the point, but still 40 lines in ST is easier than 40 lines of ladder. Plus you could simply pass the recipe number into the AOI and get rid of the loop for the specific data you need to transfer.

When you said manual I wasn't sure if that was for each child of the UDT or for each element + each child.

Paully's5.0 said:

Ok I see the point, but still 40 lines in ST is easier than 40 lines of ladder.

Click to expand...

Agreed - if it comes to doing it manually, it'll be ST regardless. I'll probably just make it a subroutine, pass it the recipe ID I'm after, and have it populate my "normal" UDT.

Was just hoping that there might be a trick to iterate through all elements of a UDT automatically

One more question on the ST structure - how do I define an input parameter? As in, I will call this subroutine from a LAD routine with an input parameter defining which array element I want to copy into the individual UDT.

So, my code will look something like...
...but somewhere, I have to tell the routine that "Pointer" is the tag that was defined as the first input parameter.

Is it just as simple as Paully's example above?

Nothing wrong with ladder! LOL ST causes a few problems when trouble shooting. Not my favourite bag.

I generally stick to ladder too - means I get less phone calls in the middle of the night but for something this simple I think I'll be safe, surely even Bubba can look at something as simple as the above and have an idea of what's going on