A.Physical separation of different electrical circuits (line & area); electrical safety
B.Limitation of bus load (telegrams) during runtime
Point A is implemented in the coupler hardware by the two communication circuits (e.g. Line and Area ) being mechanically separated and linked via an electrical transformer. Point B is implemented "in the background" by ETS during the project design stage.
1.A coupler has non-volatile memory (NVM) which stores the so-called filter table. During runtime, the coupler can check this table to see whether a telegram needs to be sent out to the other line or not.
2.On the basis of the project design data, ETS can derive which functionalities (sender - receiver communication) are distributed over more than one topology line.
Only when the sender and receiver are located in different lines/areas will ETS store this information in the corresponding filter tables of the couplers, so that runtime telegrams will be routed from the corresponding coupler first to its primary (main) line and then finally from the other coupler to the secondary (subordinate) line in which the receiver is located.
All other communication, in which the sender and receiver are located in the same topology line, usually does not need to be routed by the corresponding couplers outside this line (collection objects on the area line for accessing visualizations represent poor project development).
Coupler Operating Modes
In order to define the behavior of the coupler as described under Point B, one can select between three different coupler Operating Modes (block, route, filter).
Each of the modes can be selected separately.
•outgoing traffic* (Line à Line Coupler à Main Line)
•incoming traffic* (Main Line à Line Coupler à Line)
3.Filter Telegrams (standard behavior)
In older couplers, the filter table memory is limited to 3.5 KByte, thus limiting the number of GAs that can be filtered during runtime (the filter ability is limited to the MaGs 0...13). Because of this, such couplers have an extra parameter for the Main Group 14/15. For these main groups, the only option offered is to block or route, but not to filter. This is one of the reasons why ETS3 limits the usable GA range for a project to MaG 0..15.
ETS4/5 deliberately allows the full KNX GA range, meaning from MaG 0 to 31. This leads to the problem that all such extended group addresses can thus not be filtered by older couplers, but must be handled in the same way as MaG 14/15 (the extra parameter setting handles MaG 14/15 and all possible higher (extended) group addresses in the same way).
* Traffic refers to multicast communication only; for point to point communication (unicast), other rules apply (provided that couplers do not define their own parameter here for the filtering of unicast).
•A world coupler can be placed in the TP area line.
••TP/ RF couplers can also be used as so-called repeaters. In this case, the coupler function is switched off.