Rung Comment Attached to File:Rung
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If editing the file will only be done from a single PC then attach the rung comment using the File/Rung option. This option allows every rung to have a unique comment.
This is also a good option if you store the file on a network and different PCs all access the one network file location.
Since the comment is tied to a specific location, if a different PC performed an edit, say adding a new rung, then your PC would not know about that change and the comments would be off by one rung. This is why there is an option in the software to adjust the run comment offset. If your PC makes the change then the comment is automatically adjusted.
Rung Comment Attached to Output
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If you have more than one PC that might be editing then this is usually the best option. With this option the comment is attached to the last output on the rung.
This option allows the comment to "find" the correct rung automatically. Even if the rung has moved to a different subroutine the comment will still "find" it. So if you make an edit on your PC, my PC will still show the correct comment attached to the correct rung.
This also means if you use the same output in more than one location then that same comment will appear in both locations. Usually this is ok as using the same output on more than one rung is considered bad form. However, in some cases it is necessary (OTL and OTU, CTU and RES). If you change the comment on the OTU then you are also changing it for the OTL. One comment attaches to every location.
Now, it does attach to the LAST output on the rung which means if you have a rung with a comment and you add a branch around the output and add a second output, your rung comment would disappear. Generally best to add additional comments ABOVE the existing output branch.
Address Comments
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This attaches a comment to every location where that address appears regardless of the instruction type. You would see this comment in the logic, in the data file window, in a custom data monitor. Everywhere. This comment would display in addition to a rung comment.
Use the address comment to describe the address or the field device. DO NOT use this comment to describe what that address is doing in the logic since it will appear everywhere. Use your rung comment for that.
Instruction Comments
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This attaches to the combination of the address and the instruction type. This would allow your XIC and XIO of the address I:3/5 to have different descriptions. However, if you use the same address and the same instruction combination in another portion of your logic you will see the same comment. If you want different descriptions, use a rung comment.
The instruction comment and address comment both appear in the same space above the rung. So while it is possible for an item to have an address AND an instruction comment, the instruction comment trumps the address comment and would be the one that is actually displayed.
Page Titles
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Horribly misunderstood and underused. Page Titles are primarily used as a search tool. Page Titles identify sections of your logic and can be displayed like a Table of Contents. When you display this Table of Contents you can click and jump directly to that section. One of the features I dearly miss in the newer Logix 5000 systems.
When you select to attach your rung comment to the File:Rung or to the Last Output, this also affects the Page Title. Same rules mentioned above apply for Page Titles.
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