This page last changed on Nov 30, 2009 by knxsimulator.

Hi to all.
I have some questions about the KNX protocol.
1) Is the DLL Ack wait time 30 Bit times?
2) If a device sends a frame to another device (that is at 700m) in the same subnetwork, it is possible that while the frame is still on the bus the sender DLL retransmit the frame?
3) If a device sends a frame to a device in a different subnetwork, the ack to the sender is send by the cupler? And what about if the destination is unreachable?


Hi Callà,

The maximum allowed length for a KNX line is 350m. So it seems your line is twice the maximal length. In order to avoid the problems you're experiencing, you should add a zone coupler to separate your line in two (cheapest solution), or use IP bridging (most expensive solution).


Posted by mgallissot at Dec 01, 2009 18:51

Hi Callá,

1) I don´t have the exact time but if it is important to you i will check.
2) It is possible that a telegram will be retransmitted. Maybe not while the frame is on the bus (I suppose it is at this moment checked in the receiver electronics)
3) If the destination is unreachable it does not matter if it passes through a coupler. The coupler takes exactly the same responsibility as the original sender. It tries 3 times and then no more. If you want to make sure that the destination is reachable you have to use an additional status-object that replies on another group-address.

Posted by max reiman at Feb 06, 2010 21:39

Thanks Max.
Now all is clear.

Posted by knxsimulator at Feb 09, 2010 07:45
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