RS Logix 5000 -Could you folks please explain the purpose off Add-On Instructions ?

[Rob S.]

Good Evening ,

We received some new machinery. The machinery has a CompactLogix PLC. I took notice that they have a lot of "Add-On Instructions" within their program. The code within some of these Add-on Instructions are fairly simple , and I don't understand why they use them. Why not, just write the code in a simple sub-routine . I took notice that within these "Add-On Instructions" that the code is "gray" with no opportunity edit the code. Could you guys explain why these are used. Do they purchase , download , these Add-on Instructions or do they create them ?

Thanks so much for your help.

 

[V0N_hydro]

it allows the same add on instruction to be used multiple times in the program. like a function. the code is all encapsulated with defined inputs and outputs. It might make it easier for the machine supplier to re-use functions across different projects. re-using code that has already been debugged and tested is a good thing. they create them not purchase.

one advantage to using an AOI instead of a subroutine that is called multiple times is that each instant of the AOI is animated, you can open it and see what values are on the inputs, intermediate internal private variables, and outputs whereas a subroutine that is called from multiple places in the program you will not be able to watch it operate.

AOIs can't be edited online in allen bradley land. In schneider land they can.

 

[blperkins]

Equipment manufacturer's make their money by sending machines out the door with proven code. It does not pay to re-write standard code that is used on every machine, and add- on are less likely to generate bugs In The program.

 

[Baker in Virginia]

Ok. I see what you mean . So I can modify them , I just need to do it offline and then download , correct ?

 

[GaryS]

Think of AOI's as subroutines you can pass parameters in and out
you can use the same AOI over and over with different data.
if it's not locked you can modify them offline and download
Always keep in mind that any modifications you make will be applied to all incidents of that AOI so make sure you fully understand how it works before you make any changes

 

[bernie_carlton]

If you understand the concept of a User-defined type (UDT) as a template for the creation of the tags which hold the actual information then the AOI is a logic template. You use it to create hunks of code with a predefined fixed structure. Just as you can't modify a single tag derived from a UDT you can't modify a single instance of code based on an AOI.