Definition of terms - Basic Documentation - RMK770-1

Communication via the KNX bus

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Air conditioning controller
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Basic Documentation
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KNX bus

The KNX bus used with Synco is referred to as "KNX TP1". A full-scale KNX network is a three-level structure consisting of one area line, from which 15 main lines branch off. A further 15 lines can branch off from each main line. A network consisting of main lines and lines requires area and line couplers. If no area and line couplers are used, the network is restricted to one line.

Bus topologies

Allowed bus topologies: Tree, line and star topologies. These topologies can be mixed as needed. However, ring topologies are not allowed. The tree topology has advantages over other topologies in cases where a large network has to be created (see "Bus topologies" in the KNX bus data sheet, N3127).

Bus cable

The bus cable comprises two twisted conductors, CE+ (red) and CE– (black).

Unshielded bus cables are permitted for the KNX bus in conjunction with Synco devices. Shielded bus cables are recommended, however, if high interference is anticipated. For further details refer to data sheet N3127.

Bus access method

The KNX bus uses CSMA/CA (CSMA = Carrier Sense Multiple Access / CA = Collision Avoidance) to access the bus. With this method of access every bus user has equal data transmission rights. There is no communication master (in contrast to the master/slave principle). The data is exchanged directly (peer-to-peer) between bus users.

A collision avoidance strategy is required when several bus users attempt to send a message on the bus at the same time (multiple access). One bus user is given transmission priority, so that it can transmit its telegram fully and correctly. The other bus users stop transmitting and repeat their message after a given delay. The CSMA/CA method offers quick response times if the transmission capacity (number of connected bus users and process events) is utilized within the permitted limits.


LTE-Mode (LTE = Logical Tag Extended) is characterized by the assignment of zone addresses (logical tags) to create communications bindings to exchange process values. Devices with the same zone address exchange process values with each other, one zone address being capable of transmitting the values of many data points.

Zone addresses

The zones are addressed during local commissioning with the RMZ790 or RMZ701 operator units, or in the case of remote operation, with a PC/laptop and the ACS790 software.


S-Mode is characterized by the assignment of (logical) group addresses to individual data points to create the communications bindings to exchange process values. Devices bearing the same group address exchange process values with each other.

Group addresses

The group addresses can be assigned to the group objects (S-Mode data points) with the ETS engineering and commissioning tool (ETS = Engineering Tool Software).

Data points

For the various HVAC, lighting and security equipment and for integration into higher-level building automation and control systems, selected data points of the Synco devices can also communicate in S-Mode.

"Data points" are also referred to as "communication objects".


BK Area coupler (see Section 1.4).
DPSU Decentral Power Supply Unit (see Section 2.2.1)
E-Mode Easy-Mode, LTE-Mode is one of several Easy-Modes.
ETS Engineering Tool Software.
HVAC Heating, ventilating, air conditioning.
IP Internet Protocol
LK Line coupler (see Section 1.4).
LTE-Mode Logical Tag Extended Mode, Easy Mode used by Synco.
KNX Communications standard, wired TP1 (twisted pair).
PSU Power Supply Unit (see Section 2.2.3).
S-mode. System mode, configuration/commissioning with ETS only.
TP1 Twisted Pair 1, data transfer medium: Bus