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When to use @datatype in AVEVA / Wonderware for dynamic ControlLogix tags

When do I need to add the @datatype parameter to the item field in my tags in AVEVA/Wonderware when trying to connect to a ControlLogix? Some of my tags require the @float addition, but some of my other tags work just fine without adding anything. How do I know when I need to add or not add the @datatype?

The answer to this question depends on the default data type you have set in the device properties of the TOP Server project for your ControlLogix device. Below is an excerpt from the ControlLogix Ethernet driver help file documentation on the Default data type. Once you determine the correct default data type for your project (usually this is the data type the majority of your non-16-bit integer tags are), you add the @datatype for the other tags in the project that are not the default data type. Default Type Specifies the data type that will be assigned to a tag when the default type is selected during tag addition/modification/import.

Tags are assigned the default data type when any of the following conditions occur:

  1. Dynamic tag created in the client with Native as its assigned data type.
  2. Static tag created in the server with Default as its assigned data type.
  3. In auto tag generation, when an unknown data type is encountered in the L5K file.
  4. In auto tag generation, aliases of non bit-within-Word/DWord I/O module tags in the L5K file.
    • For example, if tag AliasTag references I/O module tag Local:5:C.ProgToFaultEn, the data type for AliasTag cannot be resolved, and thus this Default Type is assigned to it unless you specify the address as Local:5:C.ProgToFaultEn@boolean
    • On the other hand, if Alias Tag references I/O module tag  Local:5:C.Ch0Config.RangeType.0, the data type can be resolved without appending @boolean because of the . (dot) BIT that defines it as a bit-within-Word/DWord. Since the majority of I/O module tags are non bit-within-Word/Dword tags, it is advised that the Default Type be set to the ‘ majority’ data type as observed in the .ACD project. (i.e. If 75% of alias I/O module tags are INT tags, set Default Type to INT.)

Alternative Method

You can Copy and Paste your current Channel and change the default data type under the second Channel.  This lets you add tags in AVEVA/Wonderware without having to add the @ sign.  All you have to do is create a new Access Name pointing to the new topic/Alias name. Understand, however, that this will create more than one connection to the same ControlLogix. Take care in how many concurrent connection you make to the same Logix controller - while possible, too many concurrent connections can negatively impact controller and communications performance.