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Reading and writing to addresses in the device is accomplished by using tags to represent specific data points. For ACM to provide the OPC client with a list of Tags in the device, the driver must first query the device to obtain this tag listing. This process MUST BE INITIATED manually during configuration and prior to any OPC clients can read/write tags from an HMI or similar.
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By Enabling the Device Options: Enhanced logging for EtherNetIP/CIP message traffic option, the Discovery process will create detailed log entries for each step of the process that are useful for troubleshooting Listed vs Non-Listed tag related issues. |
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When using Micro 800 communications, listing structured tags is not supported. |
Listed vs Non-Listed Tags
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- The (.tsv) file is not present for this device instance in the ACM configuration for the server being used. In this case the driver will treat ALL TAGS as Non-Listed and will require the data type modifier described below.
- The (.tsv) file is present, but the tag does not appear in the file. In this case the driver did not add the tag to the file for one of two reasons:
- The tag was flagged as Reserved but the configuration option to Enable Reserved System Tag Discovery was not enabled.
- The tag was flagged as Reserved and the configuration option to Enable Reserved System Tag Discovery was enabled, however it is still not listed. In this case the tag is not discover-able by using the methods described in the publicly available documentation.
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If a tag’s External Access attribute is set to None in Logix Designer/5000, then the tag cannot be accessed from outside the controller and will not be listed in ACM. |
Polling Non-Listed Tags
Non-Listed tags can still be polled (read and write access) by following these steps:
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The driver will validate any correct pattern as described above. During the first read attempt after a tag is placed in service, the driver will check the data type entered by the user to see if it matches the reported data type issued in the response. If it does not match, the item will be flagged as Bad in OPC and will not receive a value. The driver will make an entry in the logger indicating the discrepancy. If the data type is correct, then the driver will treat the tag as a Listed tag for the remainder of its activation.
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