Essential Guide

KNX Topology - TP1 256 - What is it?

The KNX association have recently updated the topology to allow 256 devices per line without the need for Line Repeaters. This is due to a change in how bus couplers work and there now being enough products in the market to change over to the new format.


Revised KNX Topology
Revised KNX Topology



Specifically there are now enough TP1-256 Bus Couplers which take advantage of newer electronics to the reduce the data load of the device, meaning KNX telegrams can pass through more Bus Couplers before the telegram starts to lose its integrity. 


The older TP1-64 Bus Couplers are still completely supported, as is using line repeaters on a line. However, If you are using the older bus coupler (TP1-64) in a topology with 256 devices per line, each TP1-64 device is the equivalent of 4 x TP1-256 devices. So to calculate, it’s the no of TP1-64 devices x 4 plus the TP1-256 devices. As long as the total of 256 isn’t exceed the line will operate correctly.


This doesn’t change the way KNX Power Supplies work and the normal load calculations still need to take place. Given the majority of KNX Power Supplies are 640mA or less, most KNX lines will still have around 64 devices on them. Once the load limit is reached you will need to create a new line or use a line repeater to create a segment, as per the old topology.


There are some manufacturers creating larger KNX Power Supplies, such as the Gira 1280mA, which allows you to take advantage of this update to the KNX Topology.  


GIRA 1280mA KNX Power Supply
GIRA 1280mA KNX Power Supply



We have confirmed with our key manufacturers, and the majority of products we sell have the newer electronics, so there are no issues with moving over to the new topology immediately. 


If you you have any questions about this or would like specification support on any of your projects, please get in touch with the sales team.