Use the fields on the String Point tab to define the general properties for a string point. Some of these fields are common to many DNP3 points (see Configure General Point Properties). Fields that are specific to DNP3 String points are explained below:
- Length of String to Request—Specify the length of the string that Geo SCADA Expert is to request from the outstation. The length you specify here can be up to 255 characters. If the Extended String check box is selected, this field will be grayed out (that is, it will be unavailable).
- Extended String—Select this check box if the outstation supports extended strings and has an extended string at this address. If you select this check box, the Length of String to Request field will be grayed out (that is, it will be unavailable).
The current value of an extended string is transmitted as an Extended Octet String (g114), whereas the current value of an ordinary string is transmitted as an Octet String (g110).
Both ordinary and extended strings support DNP3 events. These are transmitted as g111 and g115 respectively. However, only extended strings support DNP3 status flags (which are optional for static data, but mandatory for events that are associated with extended strings).
- Level 3 Scan—Geo SCADA Expert can read DNP3 string values using a DNP3 Level 3 Scan. The DNP3 driver issues a DNP3 Level 3 scan whenever the point’s Scan Group timer expires.
- Select this check box for Geo SCADA Expert to read the string periodically from the outstation, using a Level 3 Scan.
- Clear the check box if Geo SCADA Expert is to read the string from the outstation by request only
- Confirm Set Value—Use this combo box to specify whether a confirmation dialog box is displayed whenever an operator attempts to set the string’s value (see Requesting Confirmation of Action Requests in the Geo SCADA Expert Guide to Core Configuration).