SOFT: Inheritance (object-oriented) in PLC programming?

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==> Automation List post by Jim Hanley...
To view or reply to this thread: http://www.control.com/thread/1026248755#1233456108


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Re: SOFT: Inheritance (object-oriented) in PLC programming?
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This article has some interesting points.  I was the only one to post an example that can be dissected and can also run in the background scan of a PLC (Simatic S7).  Let me me remind you that the original question was based on conformance with:

* encapsulation
* modularity
* polymorphism
* inheritance

Encapsulation: my example demonstrates encapsulation by using PLCopen blocks within the block I authored.  It uses data (unique Params structure) and functions (PLCopen motion) in a single unit.

Modularity:  my example demonstrates that this block can be instantiated by axis of many different types of Params structures to account for different mechanics.

Polymorphism: my example uses a State Output variable to represent what the axis is doing.  This block indicates movement, idle, or faulted.

Inheritance:  Okay, this is where the OOP gets a bit grey.  I'll attest that my example demonstrates inheritance in that in Simatic S7 you can use the Blk_Move command to directly address the instance of this block to be used elsewhere in the program.  Also, my example can be used as a starting point for a much more complex State Model motion block.  I'd be glad to show you my Gearing and Camming block based on the same example.

I believe my response and my example clearly show how ST programming or SCL programming with a State Model approach is as close to OOP we can get in a PLC!
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