Data on a DNP3 outstation is assigned a Class. ClearSCADA is able to poll for the data in each class independently of other classes.
An Integrity Poll causes an outstation to return any event data that is stored in its internal buffers. Use the Integrity Polling section on the Outstation Form to specify whether ClearSCADA issues DNP3 Integrity Polls to an outstation.
For Direct and Shared outstations, also use the Integrity Polling section to specify when ClearSCADA polls for Class 0 static data (see Specify When ClearSCADA Performs Integrity Polls) or use the Refresh pick action. By default, ClearSCADA also polls for Class 1, 2, or 3 data (see below) at the same time as it polls for Class 0 data.
For PSTN-only outstations, issue a One Shot or Open Line action for ClearSCADA to dial the outstation.
ATTENTION: The DNP3 standard dictates that data for a DNP3 point has to be transmitted in chronological order. If you configure a point in the outstation to generate DNP3 events, it is inadvisable to perform Class 0 Only Polls of the outstation. (A Class 0 Only Poll of a point will return the point’s current value without any preceding DNP3 event data. It is therefore possible to return the value of such a point out-of-order.)
A Class 1, Class 2, or Class 3 Poll causes an outstation to return event data for the points that are assigned those particular Class(es). Use the Class Polling section on the Outstation Form to specify whether ClearSCADA issues DNP3 Class Polls for a given class to an outstation. For Direct and Shared outstations, also use the Class Polling section to specify when ClearSCADA polls an outstation for each class of event data (see Specify When ClearSCADA Performs Class Polls). For PSTN-only outstations, issue a One Shot or Open Line action for ClearSCADA to dial the outstation.
Data is assigned to a specific class at the outstation. (If the DNP3 driver is being used for ‘transparent’ transmission of data between DNP3 devices, you also need to assign VT event data to an appropriate class, and Configure Virtual Terminal Support on the Outstation Form.)
You can use the Class n Poll Statistics attribute on each DNP3 outstation’s Status display to ascertain the number of attempted and successful DNP3 Class Event Polls that the DNP3 driver has issued since the statistics were last reset.
In addition to Class polls, the DNP3 driver is able to issue polls for specific DNP3 types of data, such as analog input events, or static String Point data. For more information, see DNP3 Event Polls, or see Specify Whether ClearSCADA Polls an Outstation for Static String Point Data, as applicable.