ProSoft Technology MVI46-DNP - Manual (Page 61)

Reference MVI46-DNP ♦ SLC Platform
Master/Slave Communication Module
ProSoft Technology, Inc. Page 61 of 143
August 23, 2007
5.2.4 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 (page 128) and DNP Subset (page
113) documentation for a definition of the level of DNP support offered by the
module.
The following topics describe each element of system design.
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 (page 112) 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.
Slave Will events be logged
before time
synchronization has
occurred? This feature will avoid logging events without the proper date and time
stamping. When the DNP slave driver is initialized, it will have the IIN bit set
to request time synchronization from the remote master unit. The master
must synchronize the time before the module will generate events. This
feature is selected using bit 8 in the module's configuration word.
Slave Will unsolicited
messages be used? If
so, how may for each
class before triggering
and what is the delay
time?
Unsolicited messaging provides the means for a slave unit to send event
data asynchronously to the master unit without a request from the master.
This requires the use of collision avoidance to prevent two or more units from
transmitting data on the network at one time.
Slave Will the module use the
secondary DNP Slave
port? The secondary DNP slave port on the module is a backup port to the primary
slave port. Only one port can be used at any one time. The module supports
automatic switching between the two ports based on several factors.