Progression from KNX TP1-64 to KNX TP1-256 Topology
Until now, the standard KNX Topology (KNX TP1-64) was limited to 64 devices per line. This was due to the inability to guarantee telegram reliability over more than 64 devices in each line segment. With KNX TP1-64, in order to install more than 64 devices on a line, a line repeater(s) (and additional power supply unit) had to be used, with the ability to add up to four-line segments together for a maximum of 256 devices on a line.

With the development of the new TP1-256 Topology, each line now has the capacity for 256 devices to be connected per line without the requirement of additional line repeaters. The is due to advancements in the electronics of the bus coupling unit (the unit that connects each device to the bus) allowing a telegram to pass through four times as many devices before it is impeded. This not only simplifies the programming of a KNX installation, but also minimises the number of line repeaters required and therefore the overall cost of the system.

Another advantage of KNX TP1-256 is that it is now possible to have 256 devices on the Backbone Line (Area 0) and Area Line (Line 0) compared to the previous restrictions of a maximum of 64 devices seen with KNX TP1-64.

However, the same device power requirements apply with the new KNX TP1-256 Standard. On the principle that the majority of KNX devices require an average of 10mA to function and, in general, 640mA power supplies are commonly used to a maximum of 64 devices per line without the addition of line repeaters.

Several KNX manufactures, including Gira (product code: GIR213800) and Jung (product code: 21280REG) are taking advantage of KNX TP-256 and have released 1280mA power supplies allowing a maximum of 128 devices per line without the requirement for additional line repeaters. Again, due to load limitations, if more than 128 devices are connected on a line when using a 1280mA power supply, then a line repeater will be required.

With 2560mA power supplies currently in development, it won’t be long until 256 devices can be connected on a line without the required of an additional line repeater, further expanding the flexibility of a KNX installation. But for the time being, the number of devices is limited more so by their collective power consumption rather than the system’s topology.

Compatibility of KNX TP1-64 and KNX TP1-256 devices

All devices manufactured and shipped after 2019 are KNX TP1-256 compatible and therefore conform to the new KNX TP1-256 regulations; devices prior this date will conform to the old KNX TP1-64 Standard. Both KNX TP1-64 and KNX TP1-256 devices are compatible with eachother and can be used together within an installation. If a mixture of KNX TP1-64 and KNX TP1-256 devices are used within a system each KNX TP1-64 device takes the place of four KNX TP1-256 devices. As long as the total number of devices is less then 256 the line will operate correctly

For more information, to see how KNX TP1-256 can benefit the design on your next project, or to double check your specification of a current project, contact a member of the My KNX Store team.

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