After switching on the operating voltage, the controller flashes for 3
to 5 seconds in different patterns.
If other patterns appear during normal operation, this indicates an
After a reset, it takes up to 5 minutes for all the connected room controllers to restart.
This is designed to avoid overloading the mains power supply when restarting. At the
same time, it reduces the load on the KNX network, as not all controllers transmit data
at the same time.
The delay is determined by the controller's device address.
In a large KNX system, the bus load can be a problem, especially with central
commands which cause the controllers to send status information simultaneously. This
can even result in the loss of data telegrams.
The management station is normally connected to the KNX bus via the area line.
Special attention needs to be paid to the load on the bus to avoid a bottleneck on
the area line. A bus load which may be acceptable on individual lines causes an
overload on the main lines and the area line.
To avoid a KNX communications overload, note the following rules and precautions:
• Define a rational topology, divided into lines and areas.
• If possible, avoid functions across lines: Place sensors and actuators on the same
• Load filter tables for the line and area couplers so that the entire system is not
burdened with information which is only required locally.
• Be rational about integration into a management station or display: Only integrate
information which is genuinely needed.
• For status messages, automatic transmission is not necessary if the display device
can actively read the values. The flags must be set accordingly in the ETS.
• Do not define too short an interval.
• Central commands which affect a large number of controllers should be divided over
several group addresses, and transmission should be staggered.
• Each group address must have a receiver to acknowledge the telegram, otherwise
unwanted repeat-telegrams are generated.
• For additional hints for reducing the bus load see pages 25 and 90.
RXB (KNX) application library
FNC Description of functions for FC-10, FC-11, FC-12
28 Feb 2009