User manual

IEC61131 User and Reference Manual
April 22, 2008
448
Object Library
The data types that are used in DNP are broadly grouped together into Object Groups such as Binary
Input Objects and Analog Input Objects etc. Individual data points, or objects within each group, are
further defined using Object Variations such as Binary Input Change with Time and 16-Bit Analog
Inputs for example.
In general there are two categories of data within each data type, static objects and event objects.
Static objects contain the current value of the field point or software point. Event objects are
generated as a result of the data changing.
In addition to the object group and variation data objects can be assigned to classes. In DNP there are
four object classes, Class 0, Class 1, Class 2 and Class 3. Class 0 contains all static data. Classes 1, 2
and 3 provide a method to assign priority to event objects. While there is no fixed rule for assigning
classes to data objects typically class 1 is assigned to the highest priority data and class 3 is assigned
to the lowest priority data.
This object library structure enables the efficient transfer of data between master stations and
outstations. The master station can poll for high priority data (class 1) more often than it polls for
low priority data (class 3). As the data objects assigned to classes is event data when the master polls
for a class only the changed, or event data, is returned by the outstation. For data in an outstation that
is not assigned a class the master uses a class 0 poll to retrieve all static data from the outstation.
DNP allows outstations to report data to one or more master stations using unsolicited responses
(report by exception) for event data objects. The outstation reports data based on the assigned class
of the data. For example the outstation can be configured to only report high priority class 1 data.
Internal Indication (IIN) Flags
An important data object is the Internal Indications (IIN) object. The Internal Indication (IIN) flags
are set by a slave station to indicate internal states and diagnostic results. The following tables show
the IIN flags supported by SCADAPack controllers. All bits except Device Restarted and Time
Synchronization required are cleared when the slave station receives any poll or read data command.
The IIN is set as a 16 bit word divided into two octets of 8 bits. The order of the two octets is:
First Octet
Second Octet
IIN First Octet
6
5
4
3
2
1
0
7
Bit Number
First
Octet
Bit
Description
0
last received message was a broadcast message
1
Class 1 data available
2
Class 2 data available
3
Class 3 data available
4
Time Synchronization required
5
not used (returns 0)
6
Device trouble