Practical_modern_SCADA_protocols_-_dnp3,_60870-5_and_Related_Systems

384 Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems
The Port Baud rate setting must be set to match the port speed of the interconnecting
device. The Port Mode selection determines the method of data transmission from the
RTU serial port (e.g. RS-232, Data Radio, Hayes Modem, etc).
In the next part, the RTU local data is assigned in groups to DNP3 classes. Note from
the configuration screen the additional ‘Buff Event’ and ‘Trig Event’ options. These
determine the behavior of the reporting of events from the RTU. The difference between
these is that the buffered events are stored for periodic transfer to the master, whereas
the trigger events are sent immediately using a DNP3 unsolicited response. This is a
mechanism provided by PDS RTUs for optimizing the use of limited bandwidth communications
systems. Its function is described in the panel following the configuration screen.
SCADA table
The RTU uses a DNP3 SCADA interface, which requires configuration of the local RTU
binary, analog and floating-point data. In DNP3 this RTU I/O is described as an object
type with an index (address) belonging to a class. How and when I/O data is exchanged
between the SCADA master and the RTU is determined by this configuration.
Objects The choice of objects can be summarized as inputs to SCADA master or
outputs from SCADA master.
Index
Class
Count
Deviation
The first DNP3 index in the group.
Class 0 or class 1, 2, 3 triggered or buffered event.
The count field defines the size of the group of points.
The amount by which the point has to change value before an event is
recognized.