DNP3 objects

Location2 is the DNP list index (or point) number of the point. When used in freezing counters ( Location5=20 ), this value determines the starting index of one or more counters to be frozen. Below is an excerpt from the DNP3 Data Object Library Documentation.

The following rules apply to the interpretation of the object point number (DNP Application Layer range field) in conjunction with objects and variations.

• Rule 1:

  Point I of object x, variation y represents the same physical point as point I, object x, variation z, where y and z are variations of object x.

  For example: A device has 16 running counters (object 20) numbered 0 to 15. Point 5 can be asked for in four different ways:

  Obj 20, var 1, range 5 returns the running value of counter 5 in 32-bit format.

  Obj 20, var 2, range 5 reports the same information, only in 16-bit format.

  Obj 20, var 3, range 5 returns the number of counts accumulated in counter 5 since the last time it was reported, again in 32-bit format.

  Obj 20, var 4, range 5 reports the same information, only in 16-bit format.

• Rule 2:

  Point I of object x, variation y represents the same physical point as point I, object x, variation z, where y and z are variations of object x.

  For example: A device has 16 running counters (object 20) numbered 0 to 15. Point 5 can be asked for in four different ways:

  Obj 20, var 1, range 5 returns the running value of counter 5 in 32-bit format.

  Obj 20, var 2, range 5 reports the same information, only in 16-bit format.

  Obj 20, var 3, range 5 returns the number of counts accumulated in counter 5 since the last time it was reported, again in 32-bit format.

  Obj 20, var 4, range 5 reports the same information, only in 16-bit format.

• Rule 3:

  Point I within different objects of the same grouping are not necessarily unique, however, within each of the binary input, binary output, analog input, analog output and counter groupings the following rules apply.

  Point I in the static object is the same physical point as point I in the event object.

  Point I in the frozen object is the same physical point as point I in the frozen event object.

  For example: For binary inputs, point I in obj 1 var 1 and 2 is the same point as point I in obj 2 var 1, 2 and 3 (static and event correlation). For counters, point I in obj 20 var 1, 2, 3, and 4 is the same point as point I in obj 22 var 1, 2, 3, 4, 5, 6, 7, and 8 (static and event correlation). In addition, point I in obj 21 var 1, 2, 3, 4, 5, 6, 7, and 8 is the same point as point I in obj 23 var 1, 2, 3, 4, 5, 6, 7, and 8 (frozen and frozen static correlation).

  Note: Point I in obj 20 and point I in obj 21 are NOT necessarily the same point. There is no direct correlation between frozen and non-frozen objects.

  For the above reason, object type 1 and 2, 20 and 22, 21 and 23, 30 and 32, 31 and 33, 110 and 111, will be considered the same, so that if a PI point is configured for an object type 30, index 1, and an object type 32, index 1 event is received, that value will be written to the point.