KNX (standard)

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Logo of the KNX standard

KNX is a standardized (EN 50090, ISO/IEC 14543), OSI-based network communications protocol for intelligent buildings. KNX is the successor to, and convergence of, three previous standards: the European Home Systems Protocol (EHS), BatiBUS, and the European Installation Bus (EIB or Instabus). The KNX standard is administered by the KNX Association.

KNX protocol[edit]

The standard is based on the communication stack of EIB but enlarged with the physical layers, configuration modes and application experience of BatiBUS and EHS.

KNX defines several physical communication media:

KNX is designed to be independent of any particular hardware platform. A KNX Device Network can be controlled by anything from an 8-bit microcontroller to a PC, according to the needs of a particular implementation. The most common form of installation is over twisted pair medium.

KNX is approved as an open standard to:

  • International standard (ISO/IEC 14543-3)
  • Canadian standard (CSA-ISO/IEC 14543-3)
  • European Standard (CENELEC EN 50090 and CEN EN 13321-1)
  • China Guo Biao (GB/T 20965)[1]

KNX Association, as of 1 March 2014, had 339 members/manufacturers from 37 countries.[2] Japan's Fujitsu General was enlisted as member number 300.[3] The complete list can be found here at

The KNX Association has partnership agreements with more than 30,000 installer companies in 100 countries and more than 60 technical universities as well as over 150 training centres.

Wire transmission[edit]

Twisted pair using differential signaling with a signaling speed of 9600 bit/s. Ideal wave resistance at 100 kHz is 120 Ω. Line resistance at 20 Ω/km, max 75 Ω/km. Maximum capacitance bus-to-bus line max 800 pF/m at 800 Hz. Higher capacitance requires proportionally shorter cable length. Bus power with 30 V DC and 25 mA[4] Polarization critical.[5] Devices within same physical segment are addressed with 8-bits[6] Maximum 57600 network nodes.[5] Media access control is controlled with the CSMA/CA method[7] Maximum segment length is 1000 m.[7] 4 segments may be connected with line repeaters to establish a network length of 4000 m.[7] Loops are not allowed.[7]

# Field D7 D6 D5 D4 D3 D2 D1 D0
0 Control[5]
R-repeated packet
1 0 R 1 P1 P0 0 0
1 Source address #0 [5]
2 Source address #1 [5]
3 Destination address #0 [5]
4 Destination address #1 [5]
5 Destination type[5]
Routing info
DT R2 R1 R0 L3 L2 L1 L0
6 User data 1-16 bytes [5]
Checksum (S) [5]

If the destination type flag (DT) is set the packet will be multicast or broadcast.[7] R2-R0 is decremented for each routing hop, like TTL in IP.[7] L3-L0 correspond to 1-16 user data bytes.[7] Source is always a physical address. Destination may be either a physical or group address.[5] Logical “0” is defined as impulse under the reference level 30 V DC. Logical “1” is lack of the same impulses.[5]

There exist an alternative interface speed at 4800 bit/s taken over from BatiBUS. But KNX TP-0 products will only operate on the same network. But not be able to exchange information with BatiBUS devices.[7]

Configuration modes[edit]

There are three categories of KNX device:

  • A-mode or "Automatic mode" devices automatically configure themselves, and are intended to be sold to and installed by the end user.
  • E-mode or "Easy mode" devices require basic training to install. Their behaviour is pre-programmed, but has configuration parameters that need to be tailored to the user's requirements.
  • S-mode or "System mode" devices are used in the creation of bespoke building automation systems. S-mode devices have no default behaviour, and must be programmed and installed by specialist technicians.

KNX Products[edit]

One of the strengths of the KNX system, is that any product labeled with the KNX trademark is not a mere declaration of the manufacturer but is based on conformity testing carried out by KNX accredited third party test labs. During these tests, it is not only checked that the device supports the KNX protocol but that its useful data is coded according to the KNX standardized Data types.

This results in devices of different manufacturers and different applications that can be combined to a working installation.

The KNX Association member companies have more than 7000 KNX certified product in their catalogues.[8] This wide range of products allow, for example, the integration of:

  • Lighting control
  • Heating/ventilation & Air Conditioning control
  • Shutter/Blind & shading control
  • Alarm monitoring
  • Energy management & Electricity/Gas/Water metering
  • Audio & video distribution

On top of that you can enable access to the system via LAN, analog or mobile phone networks for having a central or distributed control of the system via PCs, Touch screens and Smartphones.

List of KNX Open Source or Free software[edit]

You can see at Ask About KNX forum a list of KNX open source or free software.[9] There is a wide variety of software for multiple operating systems and platforms running on PCs, Macs, Smartphones and tablets with Windows, Linux, OS X, iPhone/iPad iOS and Android.

See also[edit]


External links[edit]