Practical_modern_SCADA_protocols_-_dnp3,_60870-5_and_Related_Systems

122 Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems
Qualifier Code Table
Q
Code
Range Value
Size (Bits)
0 8
1 16
2 32
Referencing
Mode
Range - Index
Mode
Interpretation of Qualifier Code
Notes
The range field contains start and stop
indexes. points are I1 to I2. I-size = 0, or 4-6
for individual object size prefixes.
3 8
4 16
5 32
Range – Absolute
Mode
The Range field contains start and stop
absolute memory addresses in outstation. Data
are Bytes B1 to B2. I-size = 0, or 4-6 for
individual object size prefixes (response
messages only).
6 - All Object Mode Specifies all objects in the referenced
group/variation. Only used for requests. There
is no range field with this mode. I-size must =
0.
7 8
8 16
9 32
Non-Ranged
Mode
11 As for I-size Object Identifier
Mode
Specifies a list of unrelated points. The Range
field contains the number of points referenced.
I-size = 0: No indexes, points only
I-size = 1: Indexes are 8 Bit
I-size = 2: Indexes are 16 Bit
I-size = 3: Indexes are 32 Bit
The Range field contains the number of
Object Identifiers following. Each Object
Identifier is preceded by a ‘Size’ field. The
size of the Size and Range fields depends on I-
size:
I-size = 1: Fields are 8 Bit
I-size = 2: Fields are 16 Bit
I-size = 3: Fields are 32 Bit
From the qualifier code table it may be seen that there are five different referencing
modes, or ways of referencing or identifying the data objects contained within messages.
Also, for some of the referencing modes there are three Q-codes applicable. These allow
for three different bit-sizes for the numbers in the range field.
The index-size sub-field
For most of the referencing modes, additional information is provided by the I-size subfield.
The specific meaning of the sub-field is dependent on the referencing mode. In each
case where the I-size sub-field is used (ie is non-zero), it gives the size of additional fields
that are given for each data object. Depending on the referencing mode, these extra fields
contain either an identifier, an index, or a number giving the object size in bytes.
The I-size codes are shown in the table below. The use of these is demonstrated in the
following sub-sections for each referencing mode.