In the balanced link mode, both the client and the server can initiate message
transfers. In the unbalanced mode, the client initiates the transmission with a
request to which the server responds.
2.4 Basic protocol functionality
The server (controlled station) delivers various data to the client.
• Data object values reported upon changes
• Data object values reported cyclically
• Responses to control commands
• Responses to read requests
The client can at any time request the present process data values by issuing
interrogation commands. The command may be a general interrogation (GI)
request, where all data objects with GI indication configured “ON” are reported.
The data objects’ GI indication configuration can also define that the data object
belongs to a particular interrogation group, 1...16. In such a case, the client can
request data interrogation values only from a specific interrogation group. A GI
request reports values from all interrogation groups.
Integrated totals counter objects can be read on demand by the client using a
counter interrogation request. Integrated totals objects can also be configured to
report the counter values when counter freeze operations occur.
The client can issue single or double commands to single- or double-point
control objects. Single controls are always direct control operations. For double
command control objects (circuit breakers, controllable disconnectors), select-
execute operations can be performed if the controllable target object allows it, but
direct control of double-point objects is always possible. Controls can be given with
or without time tags.
The client can additionally perform time synchronization commands and issue the
corresponding delay acquisition request to the server.
IEC 60870-5-104 overview
2NGA001859 A
14 REX615
IEC 60870-5-104 Communication Protocol Manual
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