IEC 870-5-101, IEC 870-5-103, and IEC 870-5-104 Protocols
IEC 870-5 protocols place more intelligence at the RTU/IED than most North American protocols. With IEC, the master station periodically issues general data polls, called Class 1 and Class 2 requests. Each poll does not ask for specific data items, such as measured (analog) or digital data points. Instead, it requests the RTU/IED to return whatever data items it determines are most important at the time the request is received.
Before running the ASE2000 in RTU Simulation mode, the user must configure and enable all messages that could be transmitted in response to Class 1 or Class 2 polls. The response to each poll request will be determined in the following order.
Information specific to a recent master request, such as a digital or analog output command, or the progress of a data interrogation request.
ASDU point information (analog, binary, totals, etc.), if such information is ready for transmission, or
A negative acknowledgement, indicating that the request was received but there was no other data to send
Responses described in the first and third items are managed by the ASE2000. Responses for the second item must be configured by the user.
Protocol Level Setup
Before proceeding to point definitions, some general RTU/IED configuration information must be entered.
For all protocols:
Data Link Address and Common Address of ASDU. Enter from Properties, Protocol specific, and the Exchange Defaults tab
For IEC 870-5-101 only:
Number of octets in the Data Link Address, Common Address of ASDU, Object Address, and Cause of Transmission. Enter from Properties, Protocol specific, and the IEC 870-5-101 tab
ASDU Exchanges
The ASE2000 supports RTU simulation transmission for all generic SCADA messages. This refers to messages containing analog, digital, and counter data points, and standard support functions such as controls, interrogations, and time syncs. The ASE2000 may not generate responses to some of the more complicated data types such as file download sequences.
Configuration is required only for messages containing input point data (measured values, binary inputs, and totals). One exchange needs to be configured for each block of points to be transmitted. To do so, the user must:
Locate the corresponding exchange
Assign it to either Class 1 or Class 2. In most cases, this is set correctly, although the default setting can be changed
Define the number of points, values, and other point parameter information
Enter the reporting frequency
Enable the message for transmission
The above actions are performed from the “Edit Exchange Properties”. Locate and highlight the proper exchange, and select Edit and Edit Exchange Properties.
The Edit Exchange menu for IEC 870-5-101 is shown below. The menu for IEC 870-5-104 is the same except that it lacks the “Data link Layer” section, as those fields are not applicable to IEC 870-5-104.

The menu for IEC 870-5-103 is:
For all protocols:
To enable the exchange to be included in a response to a general interrogation sequence, check the Interrogation box.
To enable the exchange to be sent periodically during the normal Class 1/Class 2 polling cycle, check the Transmit box and enter a reporting period, in seconds, in the Frequency field. A frequency of 0.0 can be entered if an exchange is to be sent only once, at startup.
Check the appropriate object class, 1 or 2. The most common class is already selected, but may be changed. This field is grayed-out for objects that are never included in a Class scan response.
Configuring Individual Points
Each enabled exchange must be configured to respond with data for the correct set of points. This requires the user to know the number of points to be reported, their Information Object Addresses, and other protocol-dependant properties.
For IEC 870-5-101 and IEC 870-5-104:
Each block initially contains only one point. Select Add Row once for each additional point. The total number of points is shown in the Count field 
Enter the first point’s Information Object Address in the Address field for the first row in the Information Object table
If Information Object Addresses for all other points in the block do not follow sequentially from the first, un-check the SQ box and enter address values for all other points
Point properties, including point values and quality code information, can be entered by highlighting any point and selecting the Object Properties target. The resulting menu adjusts to the type of point selected
For IEC 870-5-103
Enter the object’s Address in the Information Number field located above the Information Object table
If applicable, enter the object’s function from the Function pull-down list
Each block initially contains only one point. Select Add Row once for each additional point. The total number of points defined is shown in the Count field
Point properties, including point values and quality code information, can be entered by highlighting any point and selecting the Object Properties target. The resulting menu adjusts to the type of point selected
For all Protocols:
Select OK to complete editing of each exchange. You should save the configuration file when finished.
Responses to control (single point, double point, and analog output) and similar requests do not require user configuration. More complicated sequences not related to normal point data or control output requests, such as file download operations, may not be handled correctly. |