Poll on use

"Polling on Use" means that values are then polled from the peripherals only when the values are used, for example when a user interface has to display the values or when a Ctrl-Manager is connected to that value. "Polling on use" leads to a reduction of the communication load between PLC and driver.

When using "Polling on Use" values are only polled when a connection to the data point element has been established by a dpConnect or a QueryConnect. If no dpConnect is active for a certain data point element (no corresponding panel is open), polling for this data point is not executed.

Data point functions in the Event-Manager correspond to a normal dpConnect, so the related data point elements with a data point function are polled automatically.

A general query which the driver executes when starting up is not affected by the "Polling on Use" settings. All values with active input addresses are read.

Notes and restrictions

Configuration restrictions

It is not recommended to apply "Polling on Use" when a data point element uses one of the following configurations as that would change the configured polling behavior:

  • Alert configuration - It is impossible to use "Polling on use" with a data point element with an alert configuration. If "Polling on Use" is configured for such a data point element, this setting is rejected and a normal polling is executed. A corresponding message is written in the LogViewer.

  • Archive configuration - When using "Polling on Use" for a data point element with an archive configuration, please note that the values will only be archived when polling is performed, i.e. values are only stored when a corresponding dpConnect is active. As a result the archived values will contain gaps.

Connection query

There are always at least 2 connections (for in/output addresses) or at least 1 connection (for output addresses) on a data point element when using "polling on use". These connections origin from the driver in order to be able to track any changes in the usage by other managers. The total amount of the connections can be queried using the attribute of the data point element "_connect..total".

dpGet

When applying dpGet to data point elements which use "Polling on Use", please note that it is possible that no polling operation has been carried out for a longer timeframe (e.g. when no corresponding panel was opened). As a result the Event-Manager returns the old values. You can run a configuration query "_original.._uncertain" to check if the value is the current value. If the query returns TRUE, no polling is currently performed. To get the current value, a single query needs to be performed.

Dedicated poll groups

Addresses with "Polling on Use" should be combined in dedicated poll groups. i.e. data point elements with “Polling on Use” and without “Polling on Use” should not be mixed into the same poll group.