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.
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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 medias:
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:
KNX Association, as of September 2011, had nearly 250 members/manufacturers from 29 countries including:
The complete list can be found here at knx.org
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.
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[1] Polarization critical.[2] Devices within same physical segment are addressed with 8-bits[3] Maximum 57600 network nodes.[2] Media access control is controlled with the CSMA/CA method.[4] Maximum segment length is 1000 m.[4] 4 segments may be connected with line repeaters to establish a network length of 4000 m.[4] Loops not allowed.[4]
| # | Field | D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
|---|---|---|---|---|---|---|---|---|---|
| 0 | Control[2] R-repeated packet Px-priority |
1 | 0 | R | 1 | P1 | P0 | 0 | 0 |
| 1 | Source address #0 [2] | ||||||||
| 2 | Source address #1 [2] | ||||||||
| 3 | Destination address #0 [2] | ||||||||
| 4 | Destination address #1 [2] | ||||||||
| 5 | Destination type[2] Routing info Length |
DT | R2 | R1 | R0 | L3 | L2 | L1 | L0 |
| 6 | User data 1-16 bytes [2] | ||||||||
| Checksum (S) [2] |
If the destination type flag (DT) is set the packet will be multicast or broadcast.[4] R2-R0 is decremented for each routing hop, like TTL in IP.[4] L3-L0 correspond to 1-16 user data bytes.[4] Source is always a physical address. Destination may be either a physical or group address.[2] Logical “0” is defined as impulse under the reference level 30 V DC. Logical “1” is lack of the same impulses.[2]
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.[4]
There are three categories of KNX device:
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 almost 7000 KNX certified product groups in their catalogues. This wide range of products allow, for example, the integration of:
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.
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