Configure scan modes

A scan group is a collection of object attributes with associated data items. Scan group attributes reflect I/O points in the address space of Data Access Server whose values are polled from devices at a common update interval. The update interval for each scan group is inherited from the scan groups configured in the source DIObjects.

You can configure scan groups for OPCClient, InTouchProxy, DDESuiteLinkClient, and RedundantDIObject device integration objects. Within each scan group, you can specify data items to use as the object attributes. At run time, scan group items are updated with the latest values from the OPC DAServer according to the update interval.

The OPCClient, RedundantDI, DDESuiteLinkClient, and InTouchProxy objects contain a Scan Mode attribute that can be set for each scan group. The assigned scan mode value determines if objects are continuously updated with current data when an operator minimizes or closes the application window.

You can assign three different scan modes to a scan group:

• Active

  • Items are deleted and added to the scan group as requested (referenced) by the clients.

  • Items that exist when a scan mode change occurs are not deleted unless the previous mode was ActiveAll and the items are no longer referenced.

  • The Active scan mode polls all points that are referenced, whether active or inactive.

  • In Active scan mode an attribute is always in the active state. When the last reference to the attribute is unregistered/unadvised, the attribute is deleted.

• ActiveAll

  • Scanning is continuous and dynamic attributes are never removed when unsubscribed.

  • Items are activated by client requests, but continue to exist even after the client are not interested in them anymore.

  • Items are not removed when the scan mode changes.

  • The scan group polls the field device for all points irrespective of whether they are currently active, inactive, or even subscribed to by items.

• ActiveOnDemand

  • When the scan mode is configured as ActiveOnDemand, attributes that are not actively being referenced by any client or object are made Inactive and are not scanned.

  • New Items are deleted and added to the scan group as requested (referenced) by clients.

  • Items that exist when a scan mode change occurs are not deleted unless the previous mode was ActiveAll and the items are no longer referenced.

  • ActiveOnDemand scan mode polls the field device for currently active items only. Inactive items are not scanned.

The following table shows scan mode scan states for dynamic attributes based on whether items are referenced or not.

To set a scan mode for a scan group

1. Edit the device integration object.

2. Show the editor page containing scan groups by completing one of the following:

   • Select the Scan Group tab if you are editing a RedundantDIObject or OPCClient object.

   • Select the Topic tab if your are editing a DDESuiteLinkClient object.

   • Select the Items Configuration tab if your are editing an InTouchProxy object.

3. If necessary, add a scan group by selecting the plus sign box above the list of available scan groups.

4. If necessary, set the length of the scan group update interval in milliseconds. The default update interval is 500.

5. Double-click in the Scan Mode box of the scan group to show a drop-down list of available scan modes. ActiveOnDemand is the default scan mode.

6. Select a scan mode from the list.

7. Save your changes to the device integration object and exit from the editor.