Add-On Instructions

Hi all,

I am still in the phase of learning PLC programming, I applied for a job and when I was asked about the Add-On instructions I mentioned I don't know it. I read about it later, my understanding it is like a protocol which defines the communication between the PLC and the devices added to it. Please forgive me all if I am speaking non-technical, I am very new on PLC.

My request is please, how can I master " Add-On instructions", I want to also first understand crystal-clear the philosophy behind it.

Thanks for all in this great forum.

If you plc is AB Go to:
http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1756-pm010_-en-p.pdf
Dmargineau is faster than me.

The above references are good to read...But in short, your understanding is incorrect. AOI's are simply snippets of code (think subroutine almost) that become reusable instructions where you 'pass' parameters and the results of the AOI are 'returned'. So, for example, maybe you create a scaling instruction that accepts min/max values and a number, and the instruction returns a scaled number based on the logic you create in the AOI. The AOI block is then used in ladder just like any other instruction (MOV, COP, et al), with the added benefit you can open the AOI and see the ladder behind the instruction execute for troubleshooting. Also, once you create a library of AOI's you can share/reuse them from project to project.

Thanks"robertmee"

I am a MATLAB programmer, so I am relating developing an AOI is similar to programming a function in MATLAB which can be used later.