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Thread: Driver priority within UDT

  1. #1
    Join Date
    08.12.2016
    Posts
    1

    Default Driver priority within UDT

    How does driver priority work with regards to variables that are actually elements of a single structure in the PLC?
    We're using the Logix_ODVA driver, and virtually all of our variables are structured under a single tag.  

    i.e.: 
    BaseTag.Group1.SubGroup1.VarName1
    BaseTag.Group1.SubGroup2.VarName1
    BaseTag.Group2.SubGroup1.VarName1
    BaseTag.Group2.SubGroup1.VarName2
    BaseTag.Group2.SubGroup1.VarName3
    ...
    etc.

    Currently there are about 3000 variables (and growing), and all individual variables are separately defined in Zenon (as a collection of BOOLS, DINTS, and REALS), but are actually a single UDT in the Rockwell PLC.

    I'm trying to improve communication performance. I've disabled the Global update time and have configured 4 priority levels and assigned them to variables according to usage.  It's hard to get a good measurement of response time, but so far it doesn't feel like I'm making any significant progress.  

    Is the fact that the driver addresses all the variables via a single Logix tag preventing me from taking advantage of driver priorities?

  2. #2
    Join Date
    01.07.2008
    Location
    Salzburg, AT
    Posts
    794

    Default Re: Driver priority within UDT

    The Logix_ODVA driver reads all elements of structures and one-dimensional arrays in blocks. The blocks are acquired based on the variables whose update time (according its priority) is elapsed. So also if the update time of a variable is not yet elapsed, but the variable is in a block that was read (elapsed time of another variable in this block), the read value will be assigned to the variable. This communication protocol bases on names, e.g. name of structure.

    Thus, the use of priorities in this driver may improve performance if in PLC structures are containing variables of similar usage.

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