3127 Konnex bus KNX - Siemens

Use 

Synco and Konnex 

CE1N3127en 

17.01.2003 

Preliminary edition 17 Jan 2003 

3127Z01 

3 127 

Synco 

Konnex bus KNX 

For devices of the Synco 700, Synco RXB series 

• The Konnex bus (short KNX) unites the three existing bus technologies EIB 

(European Installation Bus also called Instabus), BatiBUS, and EHS (European 

Home System) to form the new Konnex bus standard. 

• The primary bus installation technique in the Konnex bus corresponds to EIB 

technology. Konnex enables products of different manufacture to intercommunicate 

(interworking). 

• In Synco, the Konnex bus is used to transfer data and operator inputs to the 

Synco devices. Synco uses LTE mode (easy configuration) and Konnex TP1 

(= EIB twisted pair) as the transmission medium. 

Synco devices with a Konnex interface for direct connection to the Konnex bus are: 

• RMH760 heating controller 

• RMU710 / RMU720 / RMU730 universal controllers 

• QAW740 room unit 

• RXB21.1 / RXB22.1 room controllers 

• OCI700 service interface 

The devices are certified for Konnex and are labeled accordingly by the logo. 

Siemens Building Technologies 

HVAC Products

Functions 

Transmission medium 

Mechanical design 

Konnex TP1 

Bus cable selection 

Screened bus cable 

2/10 

The Konnex bus serves as a transmission medium: 

• To commission and remote control the Synco 700 controllers and the Synco RXB 

room controllers by means of the service tool OCI700.1 

• To exchange process data between the Synco devices 

The simplest form of the "Konnex TP1" bus comprises a two-core bus cable with 

stranded lines CE+ (red) and CE– (black). 

CE+ 

CE− 

CE+ Red line 

CE+ Black line 

W Protective layer 

W 

Select the bus cable according to the country-specific offerings by adhering to the 

values indicated in the "Technical data" section. Bus cables available in EIB market 

countries as per the specifications are: 

• YCYM 2x2x0.8 Fixed installation 

EIB specification Dry, humid, wet rooms 

Outdoors (not exposed to sunlight) 

Surface mounted, flush mounted, in pipes 

• J-Y(St)Y 2x2x0.8 Fixed installation 

EIB specification Indoors only 

Surface mounted, in pipes 

• JH(St)H2x2x0.8 Halogen-free conductor, laid separately 

• A-2Y(L)2Y or A-2YF(L)2Y Underground cable for remote transmission, outdoors 

Synco or the Konnex bus allows for bus cables without screening. The screens 

available for EIB bus cables normally do not need to be connected. 

If you use a screened bus cable due to expected noise, connect the screen by following 

standard installation rules. 

Siemens Building Technologies Data sheet Konnex bus Preliminary Editon 17.01.2003 CE1N3127en 

HVAC Products 17.01.2003 

3127Z05de

Engineering notes 

Network structure 

Bus topologies 

Note 

Network address 

Notes 

The Konnex bus is based on a network structure derived from the "European Installation 

Bus", EIB. A full Konnex network consists of three structural levels. The topmost 

level is the backbone line featuring 15 main lines (medium level), each of has another 

15 lines (bottom level). The three-level network structure requires area or line couplers. 

Without these couplers, the network structure is limited to one single line. 

Permissible bus topologies at every level are: Tree, line, and star topologies. These 

topologies can be mixed as needed. However, ring topologies are not allowed. The tree 

topology is advantageous if a large network must be created (refer to "Bus topologies" 

at the end of this document). 

The term "line" is derived from the EIB environment and refers to the address range of 

a line (also referred to as subnet in Synco) and not to the bus topology "line". 

0.2.003 0.2.254 


0.2.001 0.2.002 0.2.041 0.2.042 0.2.043 

Each bus-capable Synco device (= bus device) in a Konnex network must be assigned 

a network address. 

The network address is composed of the area, line, and device address. The address is 

unique and unambiguously identifies the device location in the total network. The network 

address in KNX is also referred to as "individual address". 

• Synco devices having one Konnex interface are bus devices. These are: Synco 700 

controllers RMH / RMU, QAW740 room unit, and Synco RXB room controller. 

• If no area or line couplers are used, the bus devices use the factory-set area / line 

address 0.2. 

• If area and line couplers are used and if they are configured accordingly during 

commissioning, the area and line addresses are assigned automatically to the bus 

devices. 



3110Z24de 

3/10

Factory-set network 

address 

Device addresses 

Principles for 

addressing 

Max. 64 Synco devices 

Notes 

Device name 

Note 

4/10 

The bus-capable Synco devices are factory-set to network address 0.2.255 with 0 = 

area, 2 = line, 255 = device address. The address parts 0.2 (area, line) are displayed 

on RMZ79x operator units even though they cannot be changed. 

The device addresses must be set during commissioning. The permissible addresses 

are in range 1 to 253. Addresses 0 and 255 are predefined: 

0 is reserved in each line for the line / area coupler. 

255 is the factory-set device address upon delivery. 

Devices with address 255 do not send process data on the Konnex bus. The local 

operator unit or the OCI700.1 tool allow for accessing and assigning the device 

address. 

Address 254 normally is reserved to connect the tool (OCI700.1). (Without address 

information, the tool locates the next free address from 254 downward). 

Addressing must be designed prior to planning. Assigning addresses is easy even in 

complex plants, provided you adhere to the following principles: 

• Each device to send and receive data via the Konnex bus must be assigned a device 

address between 1 and 253. 

• Each device address may be assigned once only within one particular line (also 

called a subnet in Synco). Oftentimes, consecutive numbering starting at 1 is 

sufficient. 

A maximum of 64 bus-capable Synco devices can be installed on one line. These are: 

Synco 700 controllers RMH / RMU, QAW740 room unit, and Synco RXB room 

controller. 

• The Synco 700 option modules RMZ78x and the RMZ79x operator units as well as 

the room units on Synco RXB room controllers do not have a Konnex interface and 

thus are not considered bus-capable Synco devices. 

• The number of Synco devices in installations using third-party devices (EIB) is 

reduced by the number of third-party devices. 

An individual device name (e.g. plant designation) consisting of max. 21 characters can 

be assigned to each Synco 700 RMH / RMU controller. We recommend to define the 

name during planning. 

The device name can be written to the controller only by means of the service and 

operating tool OCI700.1. The controllers' device names are displayed on the local 

operator unit. 

The Synco 700 option modules cannot be assigned individual device names (they are 

not bus devices). 


HVAC Products 17.01.2003

Zone addressing 

Konnex LTE mode 

Planning zone 

addresses 

Integrating bus 

devices 

Bus load, 

E-characteristics 

Notes 

Clock time master 

Notes 

Synco uses the Konnex LTE mode (LTE = Logical Tag Extended). During 

commissioning, several data points are interconnected to a zone address (logical tag), 

and are thus assigned to a zone, e.g., outside air temperature, heat/cold distribution 

zone, or geographical zone (apartment, room, subzone). The data points having the 

same zone address mutually exchange process data. 

Complex plants with heating/cold generation/ventilation/individual room control, require 

careful planning of zone addresses. The zone addresses are entered using the local 

RMZ79x operator units or the service and operating tool OCI700.1 (tool only for Synco 

RXB). 

The documentation on basics for the Synco 700 controllers and the function 

descriptions of the Synco RXB room controllers contain the associated rules. 

The bus devices can be integrated anywhere in the Konnex bus by observing both the 

distance between bus devices and maximum network size. 

Each bus device has a particular bus load, the E-characteristic. This characteristic is 

considered the measure for average data traffic on the bus caused by the device. 

The E-characteristic must not be calculated for a line featuring the maximum 

permissible number of 64 Synco devices, as the E-characteristic sum of 300 is 

not reached. 

• The sum of the E-characteristics for all devices in a line must be below 300. 

• If more than 64 Synco devices will be able to be installed in one line, the Echaracteristics 

for all devices must be added to ensure that the limit value of 300 is 

not exceeded. 

• The E-characteristic is available in the associated data sheet for each Synco device 

featuring a Konnex interface. 

The Synco 700 RMH / RMU controllers can send the time (clock time master) or can 

receive the time as slaves, and can synchronize their own clocks. 

The device containing the "clock time master" function and those being operated as 

slaves or autonomous must be specified during planning. Note that the Synco 700 

controllers are factory-set to autonomous. 

• In a network, only one Synco 700 controller can be the clock time master. 

• An EIB / Konnex radio clock may also be the clock time master, but again, no other 

device on the Konnex network can then be the clock time master. 



5/10

Installation notes 

Laying bus cables 

Important note 

Bus line connection 

Bus power supply 

Decentralized bus 

supply 

Centralized bus supply 

Notes 

Terminating resistor 

Protection against 

lightning and 

overvoltage 

Important note 

6/10 

Local regulations on insulation against mains voltage (SELV as per EN 60 730) apply if 

the bus cable is laid in parallel to lines of a three-phase network (3 x AC 400 V). 

The bus lines are connected to terminals CE+ (red) and CE– (black). Observe the 

polarity of the bus lines CE+ and CE– and do not interchange them. 

In some devices, CE+ corresponds to bus terminal 1, and CE– to bus terminal 2. The 

bus connection are isolated from the device electronics. 

The bus supply at the controller is referred to as "decentralized bus supply" (= DPSU, 

decentralized power supply unit). The following applies: Small networks may contain up 

to 8 supplying Synco 700 RMH / RMU controllers (see also "Technical data"). 

As two Synco devices (with or without disabled bus supply) can be enabled per supply 

controller, a decentralized bus supply network may contain up to 24 Synco devices. 

A "centralized bus supply" (= PSU, power supply unit) is necessary for networks 

featuring more than 24 Synco bus devices and for networks featuring only Synco RXB 

room controllers. 

• A bus supply is always necessary for bus communication, i.e., either a decentralized 

or centralized bus supply. 

• Install the bus supply as close to the network center as possible to achieve maximum 

network size. 

• Synco RMH / RMU controllers in networks with centralized bus supply may not 

supply the bus, i.e., they must be set to Decentral bus power supply: Off. 

Controllers with Decentral bus power supply: On disturb bus communication. 

Konnex networks do not require bus terminating resistors. 

We recommend overvoltage protection as a simple protective measure for bus devices. 

The DEHN overvoltage protection by Siemens, order number 5WG1 190-8AD01 is a 

suitable protection. Refer to CE1P3127en for more information. 

Depending on the probability of exposure to lighting or overvoltage, complex 

overvoltage protection measures covering supply and signal lines (e.g. for outdoor 

sensors) must be considered. 

Adhere to local regulations on lightning protection and equipotential bonding. 



Commissioning notes 

Commissioning 

aspects 

Check wiring 

Check device address 

Set device address 

Set zone addresses 

Assign device name 

Technical data 

System model 

Interface data for Synco 

bus devices 

The following commissioning aspects are an integral part of proper commissioning with 

regard to the Konnex bus. 

Check the wiring prior to commissioning, and in particular, make sure that the bus lines 

are connected to the corresponding terminals CE+ (red) and CE– (black) � The bus 

line polarity cannot be interchanged. 

The devices have a factory-set device address of 255. The local operator unit or the 

OCI700.1 tool allow for accessing and assigning the device address. 

Bus devices communicating on Konnex require a project-specific device address 

between 1 and 253. The device address can be set by means of the Synco operator 

units or the OCI700.1 tool. For Synco RXB, the device address can be set only using 

the OCI700.1 tool. 

Make sure that the same device address is not assigned twice. If there is a double 

assignment, an error message "Same device address" is displayed. 

Zone addresses must be assigned to the devices if the plant functions require process 

data exchange between the bus devices. The local operator units or the OCI700.1 tool 

allow for easy assignment. For Synco RXB, the zone address can be set only using the 

OCI700.1 tool. 

An individual device name (e.g. plant designation) consisting of max. 21 characters can 

be assigned to each Synco 700 RMH / RMU controller. The device name can be written 

to the controller only by means of the service and operating tool OCI700.1. 

Konnex bus standard as per ISO / OSI (layer model 1 to 7) 

Transmission medium (bus cable) Konnex TP1 (layer 0) 

Interface type TP1 

Transceiver TP-UART (integrated in device) 

Baud rate 9.6 kbps (fixed for TP1) 

Transmission mode half duplex 

Bus power supply DC 30 V 

Power consumption bus supply 5 mA (except for QAW740) 

Power consumption bus supply QAW740 7.5 mA 

Bus supply and communication signal decoupled via throttle 

(device with integrated throttle) 

Polarity for bus lines CE+ (red), CE– (black) non-interchangeable 

Communication signal 

The communication signal (information) is transferred symmetrically to the bus lines, i.e., as voltage 

difference between the two bus lines (and not as a voltage difference to the earthing potential). The sign 

preceding the voltage between the bus lines CE+ and CE– determine the logical 0 and 1 bit values. 

Continued on the next page. 



7/10

Bus cable 

Decentralized bus 

supply DPSU 

Centralized bus supply 

PSU 

Distances and line 

lengths 

8/10 

Bus cable requirements as per IEC 189-2 (or equivalent) 

Cable type two-core, stranded (red/black) 

or 2x two-core, stranded (red/black) 

(white/yellow) 

or spiral quad 

Strands min. 5 / m 

Diameter min. 0.8 mm, max. 1.0 mm 

Wave resistance (ideal value) 120 Ω at 100 kHz 

Line resistance 20 Ω/km to max. 75 Ω/km 

Capacity, line to line max. 100 pF/m at 800 Hz 

Greater values require a proportional 

shortage of the perm. cable lengths. 

Cable screen not required (Synco devices without 

screen connection) 

Bus terminating resistor Not required 

Bus supply from Synco RMH / RMU controllers 30 V / 25 mA 

Controllers with DPSU, Decentral bus power supply: On max. 8 per line 

Bus devices without DPSU max. 2 per controller with DPSU 

Number of bus devices on one line max. 24 [8 + (8 x 2)] 

Centralized bus supply required if line has >24 bus devices 

or only RXB room controllers 

or third-party (EIB) devices 

or >2 devices without bus supply 

per device with bus supply 

Centralized bus supply: Devices with integrated throttle 

• EIB voltage supply, 320 mA, REG 

Type / Manufacturer SV/S 30.320.5 / ABB 

Supplier ID GH Q631 0038 R0111 

• EIB voltage supply, 640 mA, REG 

Type / Manufacturer SV/S 30.640.5 / ABB 

Supplier ID GH Q631 0048 R0111 

• Voltage, nominal bus supply DC 30 V 

(PSU output = DC 30 V / SELV) 

The indications for distances and line lengths in a network are designed for bus cables 

certified by either EIB or KNX. 

• The following applies to networks with centralized bus supply: 

Distance of two power supply units with integrated throttle min. 200 m 

Distance to bus unit of next neighboring PSU max. 350 m 

Distance between bus devices max. 700 m 

Total length of all lines on one line max.1000 m 

• For networks with decentralized bus supply, the distances are valid in addition in 

dependence of the number of controllers with Decentral bus power supply: On (DPSU). 

The following applies: 

Number of 

controllers with 

DPSU 

Controller with 

DPSU 

to bus device 

Maximum distance 

Bus device 

to bus device 

Total length of all lines 

on one line 

1 350 m 350 m max. 350 m 

2 350 m 700 m max. 700 m 

3 to 8 350 m 700 m max. 1000 m 

There is no minimum distance between controllers with DPSU. 



Bus topologies 

Advantage: 

Tree topology 

Branching and 

connection variants 

Note 

Permissible bus topologies are: Tree, line, and star topologies. These topologies can 

be mixed as needed. However, ring topologies are not allowed. 

The tree topology is advantageous if a large network must be created. 

Tree topology (with stub lines) Line topology (with loops) 

N2 N2 

N1 N3 N4 N1 N4 


N6 

N1 .. N7 Bus devices 

Device with 

screw terminals 

CE+ 

CE- 

CE+ CE- 




N5 


N7 N3 

CE+ 

CE- 

T-branch with 

bus terminal 

3127Z02 

Device with 

spring cage terminals 

CE+ CE- CE+ CE- 

N1 N2 N5 N6 

N3 

CE+ CE- 

N4 N8 

In devices featuring spring cage terminals, only one bus line can be inserted per spring 

cage terminal. For this reason, the CE+ and CE– terminals are available (and connected 

inside the device) in double. 

N7 

3127Z06en 

9/10

Example 1 

Distances 

Example 2 

Total length 

10/10 

200 m 

100 m 

N1 

N2 


150 m 



PSU 

400 m 

Distance between bus device 

and bus supply max. 350 m. 

Not allowed: N4 = 550 m 

250 m 

100 m 

Distance between 

bus devices max. 700 m. 

Not allowed: 

N1 to N4 = 900 m 

N2 to N4 = 800 m 

100 m 

100 m 

Bus device N4 – by adhering to the maximum distance of 700 m between bus devices 

– cannot be integrated in the bus if bus device N3 is integrated with a loop (instead of 

sub line). 

If a maximum distance of 350 m is kept between the centralized bus supply PSU and 

the bus device (without bus supply), the bus supply must be placed at location 

150 m / 250 m on the line distance 400 m. 

200 m 

100 m 

N1 

N2 


400 m 

200 m 

100 m 

N3 

N5 

Total lenght 

max. 1000 m, 

exceeded by 

N5 

100 m 

100 m 

The permissible total length of 1000 m in the line is exceeded, if device N5 is integrated 

in the bus at the given bus wiring. 

�2003 Siemens Building Technologies AG 

Subject to change 

N3 

N4 

N4 

3127Z03en 

3127Z04en

3127 Konnex bus KNX - Siemens

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