Gira 5110 00 Product Documentation page 18

i RF areas or lines of a joint KNX installation or of directly adjacent KNX installations in radio
range may never have an identical domain address! The ETS offers a function for random
assignment of a domain address for RF lines, in order to avoid this improper situation.
When the random function is used, the probability of multiple assignment of an identical
address is more or less non-existent. A domain address automatically generated by the
ETS is characterised by the hexadecimal characters "00FA..." (e.g. "00FA:4D6C3F58").
Routing counter and telegram repeat counter (expert knowledge)
In a TP telegram, the routing counter identifies how often the telegram has already been
forwarded by the area or line coupler, or the TP line amplifier. The routing counter is a 3-bit
counted measurand (values 0...7) which is reduced by "1" for every forwarding process via the
coupler or line amplifier. As soon as a bus device sends out a new telegram, the routing counter
is given the value "6". Through the permissible KNX topology with area couplers, line couplers
and line amplifiers can, and are permitted to, forward the telegram a maximum of 6 times.
Telegrams for which the routing counter is given the value "0" are no longer forwarded via the
coupler or TP line amplifier.
The routing counter value "7" is a special case which is not used by normal bus devices.
Telegrams with this value are always forwarded. The value is not reduced thereby.
With the KNX RF, the routing counter is replaced by the telegram repeat counter ("RF repeat
counter"). When a transmitter sends a new telegram for the first time, it is given the repeat value
"6". As soon as a repeater receives this telegram and forwards it, the value is reduced by "1".
For each additional repetition process via another repeater in the same RF domain, the repeat
value is again reduced by "1". Once the value is "0", the telegram is no longer repeated. With
this process, an RF telegram can be forwarded through a maximum 6 repeaters in one domain.
Only repeaters are permitted to influence the telegram repeat counter.
During forwarding on the RF side, a media coupler always replaces the routing counter of a
received TP telegram with the telegram repeat counter and the value "6". It is irrelevant which
value the routing counter has.
Likewise, during forwarding on the TP side, the media coupler always replaces the telegram
repeat counter of received RF telegrams with a routing counter and the value "6", regardless of
which value the telegram repeat counter had before.
Telegrams that are forwarded via a media coupler via the TP side to the RF side cannot be
returned to the TP side by any other media coupler. This is prevented by the "Route-Last" flag,
which is set during the forwarding process and forwarded in the RF telegram.
This limitation is important for system broadcast telegrams which are not dependent on any
domain. Therefore a system broadcast generated by a media coupler cannot be mistakenly
returned to the TP side by other media couplers.
Order No. 5110 00
Software "Media coupler / repeater"
Functional description
Page 18 of 57