User Manual

15-4
Siemens Switzerland Ltd www.siemens.com/gamma 2019
Building Technologies Division
Technical Information and Application Examples
Technical Information
System overview
Telegram structure
A telegram consists of a sequence of characters. Each character has
11 Bit, which contains a Start Bit, followed by eight data bits, a parity
Bit and a stop Bit. The telegram is a sequence of information, the bus
specific information and the user specific information. To begin trans-
mission of the information, the KNX needs to be free for a certain time
in order to start the sending procedure.
First, a control field is sent, which contains information about the
system e.g. the priority of the transmission or whether it is the first or
a repeated telegram. The control field is followed by the address field.
This consists of the source address and the target address of the tele-
gram. The source address is the physical address of the sender and the
target address of the receiving participant. The target address can be a
physical or group address. After the address field is sent out, the data
field with the user data information follows. The security field serves to
check and secure the telegram (vertical parity). After the security field,
the bus is silent for a certain time (break). After that all the addressed
participants confirm the error-free receipt of the telegram.
If the telegram is not understood right, the participant who received
that signal sends out in the confirm field NAK (Not Acknowledge) and
repeats the whole telegram. If no participant confirms the telegram,
the sender repeats the telegram.
A KNX participant sends out up to three repetitions. A telegram signed
NAK is higher prioritized than an understood telegram
(ACK = Acknowledge) which leads to a repetition of the telegram.
Addressing
Communication among KNX participants can be distinguished bet-
ween two kinds of addressing:
Physical address
The address of the product is also called „physical address“. It serves
for a unique naming for the sending KNX participant (name). Due
to this rule, the sender can be tracked. When a certain participant
is addressed, i.e. the telegram is sent to a specific device, then, the
target address is the unique physical address. This is the case when an
application program of the ETS (Engineering Tool Software) is loaded
to a KNX participant via the KNX interface. Normally, the target address
is a group address.
Group address
A group address is associated with a specific function e.g. switching,
dimming or heating. In this case, information is sent from a sensor to
an actuator function using a group address. As all KNX participants
are informed via the KNX bus they check each telegram whether the
telegram contains a group address determined for them. If the target
address is identical with a group address registered in the participant,
the telegram initiates the pre-defined function. If different push-
buttons control the same actuators, the same function can be trig-
gered by several sensors.
A participant sends a telegram with a group address and any number
of participant listen to this (multicast). Thus, one pushbutton can con-
trol different actuators and cause an execution of a function. Central
functions e.g. turn off the window-side luminaries on the South-facing
façade can be implemented in a building.
Sensors are for example pushbuttons, motion detectors, room tem-
perature controllers, brightness sensors, and combined meters for
wind speed and wind direction, binary input (e.g. window contact for
window surveillance/switching status)
Actuators are for example load switches, dimmers, binary outputs,
solar protection actuators, valve actuator for heating
Engineering Tool Software (ETS)
The ETS (Engineering Tool Software) is a
vendor-neutral software, which supports
planning, project configuration, commissioning
up to failure diagnosis of KNX systems. It is easy
and clearly structured and thus optimally suitable
for all user groups.
With the ETS, consultant engineers, planners and electrical installers
can plan the whole plant, set the device configuration as well as estab-
lish the function assignment of the sensors and actuators. After project
planning it is possible to export the single work steps and to give them
to the installer.
In principle, members of the KNX Association provide their KNX
product data base to the ETS users. The current KNX product data base
can be downloaded from the Internet, in order for the user to quickly
receive the latest data of the KNX products.
In addition to the ETS, several manufacturers offer ETSApps, which are
additional software providing specific or advanced functions for project
planning, commissioning or data transfer.
Link: www.knx.org
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