User manual

IEC61131 User and Reference Manual
April 22, 2008
487
DNP Address mapping contains multiple output points
The DNP Address Mapping table allows local Modbus registers in the SCADAPack DNP master to
be mapped to DNP points in an outstation. Each time an output register defined within the DNP
Address Mapping table changes, a DNP Write message (FC 2) is immediately issued to update the
corresponding DNP point in the outstation.
If numerous output registers that change frequently, are listed in the Address Mapping table, the
network will be overburdened with a multitude of DNP Write messages.
Recommendation: Reserve Address Mapping only for mapping of outstation DNP data that needs
to be used by the master Modbus database, or to segregate points from different outstations in the
master. If numerous points are being mapped from the outstation to the master, the system is not
designed properly. In this case, it may be worthwhile to consider transferring application logic from
the master to the outstation.
Configuration FAQ
Complimentary commonly asked questions and answers are given below.
When configuring a routing entry in the DNP Routing table of a SCADAPack, one has to specify the
Data Link Layer Timeout and Retries. Do these fields take precedence over the same fields found
under the Data Link Layer configuration panel?
Yes.
In a master-outstation architecture, how do you recommend we setup time synchronization?
Recommended practice is to configure the master to initiate time synchronization to the outstations.
DNP3 provides 4 data classes; Class 0 (Static or None), Class 1, Class 2 and Class 3. How does I
decide which class to assign any given I/O point?
In a SCADAPack controller, all configured DNP points by nature, are members of the Class 0 type.
Class 0 data is the current value or state of a DNP point. So, when a master does a Class 0 poll to an
outstation, the most current value or state of all DNP points within the database are returned.
Value or state changes on a point are captured as Class 1, Class 2 or Class 3 event data. Typically,
highest priority events are assigned to Class 1 and the lowest priority event to Class 3.
What does Class of ‘None’ mean?
Class None is Class 0 or Static.
Why does this setting do: Enable Unsolicited Responses On Startup?
This setting enables unsolicited response (or unsolicited message) transmission, when power to an
RTU is cycled or when its configuration is changed. In this case, the RTU does not have to wait for
Function Code 20 or 0x14 (Enable Unsolicited Responses) from the master before is starts sending
any collected events.
This field should be set to No, to allow a master control when an outstation is able to send
unsolicited messages. Recommended practice is to allow a master to enable unsolicited message
transmission on all outstations.
Why would I ever need to change the Application Layer Maximum Fragment Length?
The Application Layer Maximum Fragment Length determines the maximum amount of memory
that is reserved for each application layer fragment. The default is 2048 bytes on SCADAPack
controllers although outstations must be prepared to receive fragments sizes of at least 249 bytes.