KNX is a fieldbus for building automation. In the market of building automation KNX is the successor of fieldbuses EIB, EHS and BatiBus. Technically KNX is a further development of the EIB by extension to configuration mechanisms and transmission media, which were originally developed for BatiBus and EHS. KNX is compatible with EIB.

  • 3.1 Example of " turning on a ceiling light "
  • 3.2 Example " opening / closing of windows "
  • 3.3 Summary
  • 4.1 Physical structure ( = network topology )
  • 4.2 Logical structure (freely programmable)
  • 4.3 Control and Programming
  • 4.4 Package Structure
  • 5.1 Cross-platform
  • 5.2 Windows
  • 5.3 Linux


1996 started the three European organizations BatiBUS Club International (BCI ), European Installation Bus Association ( EIBA ) and European Home System Association ( EHSA ) the convergence process to find a common standard for applications in building automation in commercial and residential market.

In 1999, nine leading European companies signed from the electrical engineering and building management industry, the statutes of the new organization. The founding members of the KNX Association ( transitional initially called nexus - Association): Albrecht Jung, Gira, Bosch Telecom, Delta Dore, Electricité de France, Electrolux, Hager, Merten, Siemens, Division A & D ET and Siemens Building Technologies Landis & Staefa Division.

In the spring of 2002, the specification of KNX was released, taken in December 2003 in the European standard EN 50090 and accepted this standard as the international standard ISO / IEC 14543-3 in November 2006.

The KNX standard is an open standard, which by now have connected more than 300 companies worldwide.

Technical Basics

In conventional electrical installation, the control functions of the energy distribution are firmly connected and effected by means of parallel or series circuit. Subsequent design changes are therefore difficult to implement. Also, higher-level control functions as a central switching of all lighting circuits in a building can be achieved only with great effort.

KNX separates the device controller and the power supply from each other, to two networks, the power supply for the power supply with alternating voltage and the control grid ( = KNX ) with 30 V DC voltage. Both networks can be installed independently or in parallel in the house. There is also a power net variant in which the control signals are sent via a phase-locked mains. Powernet KNX is intended primarily for the retrofit installation. It can generally be all devices interconnected via the bus, and exchange such data. The function of the individual nodes is determined by their programming, which can be changed at any time and adapted.

The devices by different manufacturers can be fully used together in a system, assuming they have the appropriate certification by the KNX Association.

Technology of the KNX network

Between the consumer (for example, appliances, lamp, window openers ) and the mains voltage, a control device, referred to as " actuator ," incorporated. The actuator is connected to the KNX bus and receives data in the form of so-called telegrams. These frames come either directly from a sensor ( for example, switches, brightness, temperature or CO2 concentration sensor ), or indirectly by a computer that regulates what about timed circuits and other evaluations of sensor data takes depending on the programming and controls actuators enrsprechend.

Receives an actuator command, the consumer supply voltage, it turns on the power supply to the unit.

The bus line (name for example JY ( St) Y 2x2x0, 8 EIB or YCYM 2x2x0, 8) (red- black and white-yellow ) usually consists of two pairs of wires, which is used only red and black. The bus cable must at least comply with IEC 189-2, or equivalent national provision. The lines with the names mentioned above are recommended in this regard. However, as more lines as JH (St) H 2x2x0, 8 and A- 2Y ( L ) 2Y 2x2x0, 8 allowed. The pipeline diameter is 0.8 mm in general, and must not exceed 1 mm. In all lines, the installation regulations must be observed, the so-called certified EIB ( KNX ) line ( YCYM ) must also be installed directly next to power lines.

KNX system is supplied by a voltage source at 30 V DC. This voltage is supplied to bus coupling unit, each of the KNX device communicates with the other crosslinked KNX devices. By the CSMA / CA principle message loss is avoided in the case of bus collision. The KNX bus communicates with a transmission rate of 9.6 kbit / s, which is sufficient for several 10,000 devices at the correct programming. Due to the proliferation of Ethernet IP -KNX coupler were quickly developed which parent lines (range lines) can also communicate over much faster Ethernet connections and the bus can thus take advantage of the higher transfer speeds. This was also previously the maximum size of 15 field lines with 15 lines and up to 256 bus devices (actuators, sensors) expanded.

Advantages of KNX networks

With the KNX technology any type of electrical load can be operated easily and promptly. By reprogramming each port can be redefined. Thus, for example, a switch that was previously still determined to turn a ceiling light, be reprogrammed within a short time to turn on the irrigation system. Likewise, any KNX installation can query various sensor data. For example, the data of the wind meter can be used to retract blinds or awnings or close windows and doors at a certain wind speed automatically. Actions to occur, it can be set flexibly by programming the system. In this case, various trades may be connected together. Heating, ventilation, alarm, intercom, lighting and weather station can then communicate on a single network and react autonomously to changing environmental conditions.

Drawbacks of KNX

Compared to conventional electrical installations, higher acquisition costs result from an enlarged cabling requirement, which takes up more space in the installation zones. In addition, greater distribution needed to accommodate the coupler and the power supply of the bus. Similarly, the actuators and sensors must be placed and concealed in the rule. It can cost advantages when different trades ( heating, ventilation, plumbing, electrical, etc.) are combined together, there is no need for other arrangements. Ideally, each chamber has a supply and only bus, then being distributed in the first space to individual consumers.

One possible energy savings through centralized control is offset by the own power consumption of the KNX bus. Per actuator or sensor with 5-8 mA can be expected electricity demand. Therefore, actuators and sensors should be used with maximum port density. Thus, the proportional power consumption per connected or monitored function is lowered. At the same time the share of costs at the bus interface, the price per port so are lower at high port density, lower.

Examples of the use of KNX

Example, " turning on a ceiling light "

In general, the command to switch on the ceiling lamp, issued by a "normal" light switch. A person presses the switch, and the light goes on. However, the turn-on command can also be cumulative over sensors. A light sensor measures, for example, at twilight, the light intensity decreases in the room. Therefore, he issued the order to the ceiling light to turn on. However, it could continuously be always bright ceiling lights at dusk as well. When the sun is completely gone, the light comes on at maximum brightness. With this continuous dimming the room is then kept constant light. There are several ceiling lights in the room, different lighting scenarios can be programmed, provided that each ceiling light was connected separately via actuators. These can also be switched via a regular switch. About a central computer can be programmed any types of lighting on this switch in the room, since then can be navigated each individual luminaire.

Example "Opening / closing of windows "

In one room there are three windows. These have an automatic opening / closing mechanism. About one mounted in the space switch can be jointly opened by pressing any or all windows. In addition, an air quality sensor can be installed in the room. Is this bad space / stuffy air, one or all windows will open automatically and the room is ventilated. After the windows are automatically closed. In addition, this can be combined with a rain sensor. Join the rain sensor in the outdoor rain, may be issued on the EIB network command to close all windows.

Unproblematic, these functions can also be combined with other systems ( = trades ).

It is conceivable, a coupling with the locking system. When the door closed, all open windows are automatically closed in the house.

It is also conceivable combination with a gas sensor. If natural gas out of a gas pipeline and is focused around the boiler room, this can register a gas sensor. All relevant windows are then automatically opened to allow the gas evaporates. In order for a gas explosion is prevented. In addition, closing the gas main conduit, a controllable electric clutch, so that no further gas continues to flow into the room.


Using KNX can be

  • Lighting
  • Shading
  • Heating
  • Climate
  • Ventilation
  • Alarm
  • Information
  • Remote access (via mobile phone, smartphone, telephone, Internet)
  • Centralized control of the house

Integrated interconnect.

Structure of KNX

Physical structure ( = network topology )

The KNX is divided into 15 areas, each with 15 lines and 256 participants per line. Required active coupler counts as a node, thus reducing the maximum number of participants. Thus can be controlled individually to ( 255x16 ) = 61455 255 x15 bus devices. This referred to as the Physical Address 8.7.233 in area 8, line 7, the participants 233 coupler will always receive the subscriber number 0

64 bus (TLN ) can be connected per line. This number is determined by the voltage supply. To extend a line, a maximum of three line amplifier can be installed. It thus creates three additional line segments with turn up to 64 TLN. The coupler and the amplifier count as participants, thus reducing the number of possible devices on both 63 TLN. Each segment requires a power supply.

To extend the lines, in their structure, they are connected by a so-called main line. For this purpose, the lines are connected by a line coupler with the main line. The main line in turn requires at least one power supply and can contain up to 255 bus devices. A main line connects a maximum of 15 lines to each other and forming a region.

A field line or backbone than 15 regions can be connected together. The field line uses at least one power supply. A maximum of 255 participants per region, including the 15 lines are involved.

On the parent lines, main line and area line, are usually devices that provide central functions involved. These are, for example, physical sensors, visualization, logic components and actuators in distribution, the switching outputs for sensors from different lines provide.

Logical structure (freely programmable)

The collection of actuators and sensors are connected to a so-called group address, which can be easily programmed. This gives the possibility to change the togetherness, for example, switches and lamps at any time without having to lay new cables.

The communication between the devices is done with standardized commands. This ensures that devices from different manufacturers to work together. For the first time, a uniform standard has been created which is open to all manufacturers of electrical equipment and control components. Meanwhile, hundreds of thousands of buildings were equipped with a KNX system worldwide. Is correspondingly large and the diversity of control devices of different manufacturers.

KNX is an open standard, that is, each manufacturer / developer has full access to all necessary technical information that it needs for further development. However, this requires the contributory membership in the open Association KNX Association. Therefore, there is criticism that this is not really an open standard, because basically paying a price for membership. Only when this membership is also free of charge, can be of an "open standard" speech. Here, however, recognize that this is a common and very effective, especially for smaller companies way to obtain the necessary patent rights.

Control and Programming

The programming of the participants and assigning the group addresses is done using a special, but also standardized software, the Engineering Tool Software (ETS). The ETS is provided by the umbrella organization KNX Association and ensures the smooth cooperation of components from different manufacturers (now over 175 manufacturers in the world ).

The KNX standard has now been adopted by the U.S. and many Asian countries for building houses.

All major manufacturers of electrical installation products and heating equipment suppliers now offer KNX - compatible devices.

As a successor to the EIB KNX standard in 2002 was from the nexus Association (now KNX Association) developed according to the standard EN50090. KNX is backwards compatible with the EIB, so that existing EIB systems are expandable with KNX - box modules.

Packet structure

The control byte defines the packet priority and distinguishes between a standard and an extended package:

The retry bit R so that participants who have already received the packet correctly, can ignore the repetition of the first sending of packet 1, in a repeat of 0.

The priority levels are allocated to the bits:

The source address (. . Typical spelling ) consists of two bytes, the MSB is transmitted first:

The destination addresses either an individual receiver ( uni- cast) or a group ( multi-cast; typical notation: / / ); the type of the target address is set in DRL byte. In a physical address corresponding to the encoding of the source address. A group address is encoded differently:

The structure of the DRL - bytes ( from destination - address- flag, routing counter, Length) is

The routing counter R0 .. R2 is initialized with 6 and decremented by each line and area couplers. A packet with the value 0 is discarded. A value of 7 prevents a decrement and leave the package as often as forward. The bits L0 .. L3 enter the length of the following user data to minus two, ie = 0 corresponds to a length of 2 bytes, length = 15 corresponds to 17 bytes.

The Transport Layer protocol control information ( TPCI ) describes the communication in the transport layer, for example, establish a point-to -point connection. The Application Layer Protocol Control Information (APCI ) are for the Application Layer Services (read, write, reply, ...) responsible. A possible variant of the payload is the standardized communication to EIS (EIB Interworking default). Here, there are 15 different EIS formats:

The checksum is an inverted, bit-wise XOR of all previous bytes sent the packet.

In a Longframe even N> 255 octets are possible.

Software frameworks


  • OSGi - middleware standard ( Java Framework) for the integration of EHS / CHAIN ​​, EIB, connections, LON, etc. in service gateways
  • OpenHAB - Java / OSGi -based integration platform for the use and integration of KNX with other protocols such as home Matic, 1-Wire, etc.
  • Mister House - Perl - based framework for home automation (EIB, X10, etc. )


In the 1990s, the OPC (OLE for Process Control) has been developed as a standardized software interface for the Windows platform to facilitate the integration of various, hitherto mostly manufacturer -dependent and thus proprietary automation buses in a system. Originally based in the industrial automation, drew rapidly from the possibility, through interdisciplinary OPC with other areas - such as, for example, building automation - to be able to act.

With the OPC server came in 1998 consequently the software tool on the market, through the integration of the EIB (KNX) has been greatly simplified in hybrid automation systems. How can today create software solutions, such as heating and lighting control to merge homogeneous classical building functions of a production facility by the EIB and the visualization and automation of industrial production process over other bus systems. The coupling of different buildings buses, such as EIB and LON, to an integrated management system is easily possible through the existing OPC Server for KNX and LON.


Variants of KNX networks

  • Cable -guided KNX (architecture comparable with an ethernet. )
  • Type TP- 0: transmission at 2400 baud. This version comes from the BatiBUS standard.
  • Type TP -1: transmission at 9600 baud. This version comes from the EIB standard.
  • Called Powerline, also Powernet ( The phase-coupled power lines serve as a network medium, thus no separate bus lines are required. )
  • Type PL -110 transmission with 1200 baud to 110kHz. This version comes from the EIB standard.
  • Type PL -132: Transmission with 2400 baud to 132 kHz. This version comes from the EHS standard.
  • KNX -RF, radio transmission on 868MHz ( Here, the components via radio controlled ).
  • KNXnet (newest development. Merger of the networks and LAN The entire KNX building automation is controlled via a computer network (Ethernet). )

Networked home appliances

The renaissance of KNX approaches also reflects the trend in the white goods towards "networked home appliances ." This currently leads mostly over Powerline solutions, where the favored by the Ceced EHS has clearly established itself as a manufacturer-independent standard.

With respect to the focus is less EHS on Sensor-/Aktor-Technik as to the specified protocol frames ( " objects "), with which the control of the individual functions of home appliances is carried out.