Function | Function as media coupler
RF/TP media coupler/repeater | Order no. 5110 00 | 51103300
Page 22 of 42
probability of multiple assignment of an identical address is more or less non-
existent. A domain address automatically generated by the ETS is character-
ised 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 permiss-
ible KNX topology with backbone 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 re-
peater 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/segment 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/segment coupler always re-
places 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/segment coupler via the TP side to the RF
side cannot be returned to the TP side by any other media/segment 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/segment
coupler cannot be mistakenly returned to the TP side by other media/segment
couplers.
