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Then a sequence of 0 up to N I-frames with ASDU 100 [Interrogation Command] and ASDU 101 [Counter Interrogation Command] is sent, both with CauseOfTransmission=6 [Activation]. The I-frames are sent for each station with at least one input I/O tag (i.e. Ai, Di, Qi, Ci). As a response, there is expected The expected response (in any order) is:
- reception of frames with ASDU 100 [Interrogation Command] and with CauseOfTransmission=7 or 10 (depending on the Command Confirm parameter)
- reception of frames with ASDU 101 [Counter Interrogation Command] and with CauseOfTransmission=7 or 10 (depending on the Command Confirm parameter)
- reception of current values of all I/O tags.
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The D2000 system also supports a balanced mode. In the this mode, the task of controlled and control stations is symmetrical. In this mode, the D2000 system receives commands and confirms them. The balanced mode may be used only when it is supported by the partner station. An advantage is that the D2000 system sends the current status of output I/O tags (defined as ASDU 1-40) as a reply to ASDU 100 [Interrogation Command] and 101 [Counter Interrogation Command] requests. It is still suitable to configure single-shot commands as ASDU 45 - 64; they are not repeated after re-establishing the connection.
As the protocol supports the balanced mode (partly it is a server), the rules of server protocols apply to it.
The output tags, which are configured as ASDU 1-40, do not go through the Transient status (i.e. they are considered as if in the configuration of I/O tag, Output control tab, the I/O tag output mode is set to Command). The writing is considered to be successful if there is a connection with the server at the time of writing, otherwise, the writing is unsuccessful.
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