Multiple logic threads within a single ladder rung

[Flex727]

I have the unfortunate task of re-creating and updating a project written by someone else some time ago and all I have is a printout of the ladder logic. The problem with this is that the original programmer did not seem to understand that you should not have two or more separate logic threads within a single ladder rung (i.e. multiple unconnected terminations on both the left and right sides of the ladder). I haven't ever done this and I'm wondering if VisiLogic compiles the program correctly when this mistake is made. In other words, I am separating out the logic properly - should I expect the compiled program to operate exactly the same?

[Joe Tauser]

Somewhere along the line they made multiple threads a no-no in the OS.  Break them out.

 

Joe t.

[Flex727]

Oh, I'm definitely breaking them out. The question is: will the PLC logically function differently after the multiple threads are broken out? I'm re-creating something that originally worked and all I have is a printout of the ladder.

 

This is for a V120, by the way. I'm not sure when the code was written, but the date of the printout is 2004.

[cantcliff]

You may have to step through the logic for each one to make sure.

 

Anytime something is compiled/translated there's always a chance for error in the final product if the logic doesn't follow a strict guideline convention.

[Ausman]

Hi Flex,

 

I have 2 observations/suggestions.

 

1).  Is the printout an actual copy of the program that supposedly worked?  Or could it be something printed during development, that someone else has been told is a "copy of the program"?  ie are you sure that the print is the exact code that was in the controller that worked?  It all sounds a bit sus to me.

 

2).  Why reinvent the wheel?  It might be a good starting point to do things exactly as written and see how/if it runs.  I'm sure you can get copies of older versions of programs and O/S's by asking nicely here.  Write it as printed, put it all in and see how it goes.  If it works then you are one step ahead.  If it doesn't then you are a bit back to point 1), but at least you have a much better idea.  No point working on something if your baseline is totally incorrect.

 

Cheers,

Aus

[Flex727]

Thanks, Ausman. Unfortunately, there's no way to know if the printout is the last version, but I suspect it is since printing out the code takes so much time and produces so many pages. I should have the new V120 in my hands in a few days and I'll test the code out.