Topology

Diagram 3: Architecture for a KNX/EIB Network

Basically all types of topology are allowed to connect devices, which give a big advantage towards the endless possibilities of scalability in the design. Still there are 3 levels for interconnection within the topology as shown in Diagram 3.

One line can have up to 64 devices, so if we want to connect more components into that line it is not possible. The solution is to put a main line with two line couplers (e.g. AL1 and AL2), for AL1 we can have up to 64 devices including the coupler and the same is for AL2. This expansion continues on the main line for up to 15 lines as shown in Diagram 3 and it becomes an Area, which the again can be connected to a Line Area. The Line Area can have up to 15 areas. It is very important to notice that each Line has to have a coupler and its own source, regardless of what type of line it is. The source and coupler are crucial as they physically separate the lines and areas, and are responsible for correct routing. Each Line regardless of its type can also support up to 64 devices, including the couplers. By adding up all the devices, a complete system can support up to 14.400 devices.

Figure 9: Example of an addressing group assignation to devices.

Figure 8: Group Addressing Scheme in KNX/EIB

Diagram 4: Addressing Example for Devices

The addressing method is very important in order to correctly identify devices within the system. There are two types of addressing:

- Physical Addresses

- Group Addresses

The physical address indentifies the device with correspondence to the physical location within the topology of the system. The physical address is composed by 3 sections, the first one identifies the area where the device is located, followed by the line and ending by the number of the device (area-secondary line-device). For example the address given by 1.15.2 indicates that the device is located within area 1, Line 15 and is the 2^nd device in the Line 15 as shown in Diagram 4.

The group address is used to define specific functions of the system. It is a format as shown in figure 8. Its assignation is of free design for the installer. For example, the main group can represent general functions such as lights, HVAC, Motors, etc. The intermediate group can represent a physical location of the house, living room, kitchen, bathroom, etc. The last group of 8 bits can represent the number of device located within that room. Even if the design is free, it is strongly recommended to keep the same design for all the projects, as it becomes simplifies future control check-ups.

KNX/EIB has an application program ETS, where several parameters and communication objects can be pre-defined.

Data Transmission

Figure 10: Telegram Format Fields in KNX/EIB

As soon as an event occurs, it is detected by a sensor, which in response sends a telegram. This event can be random, e.g detection of presence, or it can be cyclic, turning the lights every day at a given hour. The telegram is sent following the CSMA/CA protocol. If the receiver gets the information and is correct, it responds with an acknowledgment, ACK, otherwise there is no response at all. When there is no response, retransmission takes place automatically for a given number of iteration.

The telegram is formed by seven fields, six for control requirements and one for the data, as shown in figure 10. At 9600bps, the transmission of a byte needs 1d.35ms, and the transmission of a complete telegram needs between 20 and 40ms.

Once the installation is finished and the conventional communication takes place, the group address will be included within the destination field, which allows sending control orders to sensors and actuators. These orders are included in the data field and are defined by the EIB Interworking Standard EIS depending on their size and function.

The EIS contains the data for each function that has been assigned to the communication objects. According to the standard, there are seven different communication objects, each one assigned to a type of control action (communication, light regulation, sending an absolute value, floating point values, etc.). In this way it is possible to guarantee compatibility among devices from different manufactures.

Programming the physical address to the device according to the topology that has been used.

- Load the libraries, data bases, plugins and utilities created by the manufactures for the specific devices into the ETS.

- Configure the application, based on the parameters that each component will need.

- Assign group addressing between devices to unify sensors, actuators, controllers and communication objects.

- Load the programmed application of ETS into the installation.

ETS Program

ETS is a commercial software tool which has been specifically developed for KNX/EIB to program home automation devices.

Programming the devices is the last part of the installation. A PC is connected through a gateway (RS2323, USB or IP) into the installation. Then the following steps take place:

- Programming the physical address to the device according to the topology that has been used.

- Load the libraries, data bases, plugins and utilities created by the manufactures for the specific devices into the ETS.

- Configure the application, based on the parameters that each component will need.

- Assign group addressing between devices to unify sensors, actuators, controllers and communication objects.

- Load the programmed application of ETS into the installation.

Introduction to Home Automation

The basic elements are defined as:

- A sensor connected to coupler.
- A coupler with a Micro-controller "Intelligence"
- An actuator, which responds to the sensor's instruction.
- The bus line, through which the information flows.

Note: If the coupler is separated from the sensor, you can connect different types of sensors to it. Some keyboards come with the coupler integrated, in that case it is not possible to connect other sensors into that coupler. And always, one sensor for one coupler.

A domotic component if formed by the sensor (keyboard), the coupler and the actuator. Therefore each component must be from the same manufacturer so they can comunicate properly.

On the other hand, different components can be from different manufacturers and they can communicate with each other, thanks to the KNX Standard. (Notice: this only applies for KNX manufacturers).

THE WIRING:

The sensors and the coupler are only connected to the red-black wire low voltage, where the information is sent.

The actuator has a connection to the bus (red/black wires) in order to get the info. And it is also connected to de AC current by the conventional wires.

NO LOOPS: It is crucial not to have any loops on the red-black wiring, otherwise the components can get damaged.