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.