The server (controlled station) delivers various data to the client.
- Data object values reported upon changes
- Data object values reported cyclically
- Responses to control commands
- Responses to read requests
The client can at any time request the present process data values by issuing interrogation commands. The command may be a general interrogation (GI) request, where all data objects with GI indication configured “ON” are reported. The data objects’ GI indication configuration can also define that the data object belongs to a particular interrogation group, 1...16. In such a case, the client can request data interrogation values only from a specific interrogation group. A GI request reports values from all interrogation groups.
Integrated totals counter objects can be read on demand by the client using a counter interrogation request. Integrated totals objects can also be configured to report the counter values when counter freeze operations occur.
The client can issue single or double commands to single- or double-point control objects. Single controls are always direct control operations. For double command control objects (circuit breakers, controllable disconnectors), select-execute operations can be performed if the controllable target object allows it, but direct control of double-point objects is always possible. Controls can be given with or without time tags.