About This Application Note: Tags are variables (such as communication points in field equipment, calculation results, alarm points, and so forth) that are used in screens and worksheets. For detailed information about tags, tag values, and tag properties see Working with Tags . Data Flow Each IWS module contains a virtual table of the tags that are relevant for that module at the current time. The Tags database uses this table to determine which information must be updated in each module. For example, the Viewer contains a virtual table that lists all tags configured for all of the open project screens.
If a tag value changes, the Tags database sends a message to the Viewer , and then the Viewer updates the value in all objects where the tag is configured. For example, if a driver reads a new value from the PLC, the driver updates the tag associated with this value in the Tags database. Then, if this new information must display on the project screen, the Tags database sends the new tag value to the Viewer task, and the Viewer updates the screen. Data Flow Example Note that the driver does not send new tag values directly to the Viewer .
In addition, there is no pooling between tasks — the Tags database receives the updated information and immediately forwards it to all runtime tasks requiring that information. Important: The Viewer module will update an object only when (at least) one of the object's tag values change. If you configure an object animation (such as Text Data Link ) with a function that does not require a tag (for example, NoInputTime() ), the Viewer will not update the object because there is are no tags associated with that object. The architecture of IWS significantly improves the internal data flow performance and makes it easy for you to add new internal tasks.
Even though each task works independently, it can access information from any other task through the Tags database. Executing/Switching Modules IWS is a SCADA system composed of modules that must be executed simultaneously. Based on the multi- tasking concept, each runtime module ( Viewer , Driver , and so forth) is a thread and the operating system Page 20 InduSoft Web Studio