TN AppSvr165 Understanding Application Server IO Scan Modes
Description
This guide from InSource will help you understand the scan modes in application server when talking to IO. The options are:
Active
ActiveAll
ActiveonDemand
- Author: Mike Viteri
- Published: 11/9/2015
- Applies to: Application Server
Details
The differences between the scan modes are listed below
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.