Announcement

Collapse
No announcement yet.

Processing order for multiple coils in a rung

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts


  • Processing order for multiple coils in a rung

    Hello. If I have multiple output coils or box instructions in a rung, all powered from the same leg, do they get processed from top to bottom, simultaneously, or is the processing order undefined? I'm assuming it's top-to-bottom. I've been using this style to group some functions together (for instance to format data prior to using it in a box instruction) and I'm wondering if I'm playing with fire doing it this way.

    Thanks, Andrew.


  • #2
    Basically, all the input logic gets resolved, then the outputs are resolved top to bottom.

    Note that the top left corner of some of the boxes have an "asynchronous" colored flag that tells you if it's a "multi-scan" (e.g. a TMR) or fully asynchronous (e.g. MRX - Modbus Write in that those instructions are actually sending/receiving data while the PLC logic is going on), and take more than 1 scan to finish, and typically have On Success and On Error bit flags.

    But for a majority of the output instructions like OUT coil, MOVE box, etc., they are executed top to bottom and complete as they are executed.

    There is one "midline output" ladder rung construct that is slightly different. I utilize this using a NOT contact to implement an "if then/else" logic behavior that behaves as you would expect. Let me know if you have questions about that.


    There are 10 kinds of people in this world, those who know binary, and those who do not.

    Comment



    • #3
      Thanks for the quick response. Now I can rest easy knowing I don't have to rework my code! Happy 4th.

      Comment



      • #4
        If you look at the monics for a rung, that's basically a to-do list that the PLC follows, so that will tell you the order (except for asynch instructions like Franji1 notes).

        Comment



        • #5
          Originally posted by ControlsGuy View Post
          If you look at the monics for a rung, that's basically a to-do list that the PLC follows, so that will tell you the order (except for asynch instructions like Franji1 notes).
          Look at the Project's folder <project name>_EXPORT_DMD.TXT file in Notepad to see the mnemonics in text form.
          There are 10 kinds of people in this world, those who know binary, and those who do not.

          Comment



          • #6
            Thanks gentlemen.

            Comment

            Working...
            X