ProSoft Technology MVI71-DNP - Manual (Page 94)

MVI71-DNP ♦ PLC Platform Reference
DNP 3.0 Master/Slave Communication Module
Page 94 of 172 ProSoft Technology, Inc.
August 23, 2007
5.3 Designing the system
System design defines the data requirements of the system, communication
parameters, and module functionality. The application developer should refer to
the person responsible for the DNP master and slave device configurations to be
certain the functionality and data types required for the whole system are
consistent. Review the DNP Device Profile and DNP Subset documentation for a
definition of the level of DNP support offered by the module.
The following topics describe each element of system design.
5.3.1 System Design Considerations
In order to implement a solution using the module, the PLC must be set up using
both program and data files. The data transfer interface requires ladder logic in
order to interface data in the module with that in the PLC. Data is transferred
between the module and the PLC through BTR and BTW instructions. These
data areas are shared data regions available to both the processor and the
module. The ladder logic required is discussed in the ladder logic section. This
program interacts with the module by sending and receiving data.
Before you generate the program or layout the data files, you must first design
your system. Time spent doing system design at the outset of the project will
greatly enhance the success and ease of development of the project.
DNP Functionality Review
This phase of design defines the features of the DNP Level 2 Subset supported
by the module and to be utilized in the specific application. For example, will the
unit use unsolicited messaging? Coordination with the DNP master developer is
required to be certain the host will support the functionality you select. If a DNP
master port is to be used, the parameters required to communicate with the slave
devices must be known and considered in installing and configuring the module.
The features that must be defined in this design step are as follows:
Mode DNP Feature Discussion
Slave Is collision
avoidance required
for the primary DNP
port? Collision avoidance is required when unsolicited messaging is
used. Any node on the network (master or slave) can transmit
a message when data is ready. Collision avoidance prevents
two or more units from transmitting data at the same time. This
feature requires special cabling and timing considerations. It
will only operate in RS-232 mode, and is not supported in RS-
485 or RS-422 modes.
Slave Will the module use
events and the
Report by Exception
feature? If the DNP Slave driver will generate event messages, they
must be retrieved from the module using class polls or polls for
the specific event objects. Refer to Event Size Computation for
computing event size for digital and analog inputs.
Slave Will analog events
be returned with or
without a time
value? The default for analog events is to return them without time.
This is as specified in the DNP Subset document. The module
supports analog event reporting with time. This is selected
setting bit 5 in the configuration word (offset 21) for the module.