User manual

IEC61131 User and Reference Manual
April 22, 2008
455
SCADAPack DNP Outstation
A DNP3 Outstation can be considered the base class of all terminal nodes on a DNP network. All
other DNP3 configuration modes, such as Master, Mimic Master or Router, as implemented by the
Control Microsystems DNP driver, inherit their properties from the outstation base class. In other
words, a SCADAPack controller can simultaneously take on any other operation mode, in addition to
being a DNP outstation.
When configured as a DNP outstation a SCADAPack controller is able to:
 Map physical I/O data to DNP points.
 Define DNP points as Class 0 (Static or None), Class 1, Class 2 or Class 3 data types.
 Respond to requests from one or more master stations such as a SCADA hosts or other
SCADAPack controllers capable of operating as DNP Masters.
 Initiate unsolicited responses to one or more master stations.
Note: ‘Unsolicited responses’ are also known as ‘unsolicited messages’. ‘Unsolicited
messages’ will be used predominantly in this document.
One distinguishing feature of a DNP outstation is this ability to trigger unsolicited messages to a
master, upon event accumulation. Events are accumulated when the state of a DNP point changes or
an analog values exceeds a threshold. Dead bands can be used to filter out noise from being reported
as event data.
After accumulating a certain number of DNP events, or if a certain time period has expired, a DNP
outstation will trigger an unsolicited message all its configured master DNP stations, reporting event
data. As defined by the DNP specification, an outstation that triggers an unsolicited message expects
a confirmation from all the targeted masters (or peers). If an acknowledgement is not received with
a configured Application Layer timeout, the outstation will retransmit the initial unsolicited
message. If no response is received within the Application Layer timeout, the outstation will
retransmit again. This process continues until the outstation has retransmitted the message a number
of times as configured by its Application Layer Retries parameter.
If all retry attempts fail, this message is discarded from the transmit buffer. As of this writing, re-
transmission of the failed message will only resume after a new event occurs within the appropriate
buffer. Future releases of the SCADAPack DNP driver will re-attempt a failed DNP transaction after
a random period of time has expired. Retransmissions will be attempted until the messages are
eventually received by the master.
Application Layer messages that are larger than 249 bytes are broken down into Data Link frames.
The DNP protocol allows one to configure acknowledgements of individual Data Link frames, this
enhancing network robustness, especially under noisy environments. When the underlying network
structure is noise free (wired or networks for instance), enabling Application and Data Link
confirmations are not necessary.
How to Configure SCADAPack DNP Outstation
In this exercise, we will configure a DNP outstation with address 10. We will also configure the
station with digital input points associated with Class 1 and Class 2 events. The station will be
configured to trigger unsolicited messages to Master station 200, when Class 1 and Class 2 events
occur on these digital inputs.
After this exercise, you should be able to: