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of the KNX Association in 1999 and the publishing of the KNX Open Specification in 2001,
the first device being manufactured in 2002. KNX, also known as Konnex, was approved as
a European Standard (EN50090) and International Standard (ISO/IEC 14543) for building
automation systems.
A KNX network utilises a twisted pair to send data, as a conditioned signal superimposed
on the supply voltage, to all the devices in the system via the characteristic green cable. The
two wires are press fitted into a bus terminal, which can accommodate up to three cable
connections and is the standard component for connecting KNX devices to the network.
The KNX system may be freely branched and the only restriction in topology is that it
cannot form a loop at any point, although branching does reduce the maximum length
of any line, which has a nominal maximum length of 1 km. The system implements five
levels of the OSI model and passes all values as bit and byte values within the bus tele-
grams without units. The basic unit of a KNX installation is a line, which along with its
conditioning power supply can accommodate up to 64 devices, although repeaters can be
added to allow up to three further sections each containing 64 devices to be added. The
conditioning unit with the power supply is known as a choke. Further lines can be added
to the system either to add more devices or to split the topology into sensible geographical
segments for system management. Up to 15 lines can operate within one area, each line
requiring a line coupler and its own conditioned power supply. Up to 15 areas can be com-
bined on a backbone, each area requiring an area coupler and its own conditioned power
supply. In general, line and area coupling is performed by the same device, reparameter-
ised. The system transmission rate is 9600 bps and the green cable can be laid alongside
mains electrical wiring, easing installation. Devices that translate between KNX and other
systems facilitating intersystem communication are known as gateways. There are gate-
ways available for the vast majority of significant communication systems.
All certified devices carrying the KNX mark are guaranteed to be fully compatible with
the system. The system is programmed using engineering tool software (ETS), a single,
standard program for design, programming and diagnostics. Within ETS each device is
assigned a physical address that consists of a unique three part number defining the area,
line and device number. Depending on the application module to be used, there may be a
large number of programs available, offering a widely varying range of parameters. These
parameters, called objects, are the functions available, and interaction between devices is
achieved by linking objects within logical addresses called groups. In this way a particular
function may be added to a number of groups and used in many different ways simultane-
ously within a system. When programming the physical address into a bus controller unit,
physical presence is required as a programming button has to be pressed on the device,
but all further programming can be performed without direct access to the device. The
system can be programmed locally via a USB interface or wirelessly or remotely via an
Internet Protocol (IP) gateway.
KNX was designed specifically as a system for building control, so was never intended to
directly transmit and manage high bandwidth information. It provides transmission speeds
suitable for such requirements, is easy to install alongside mains cabling and is very amenable