The Home Automation Bus system, to facilitate the installer’s work and to limit the length of the cables of connection, can take a type of free-standing, following star schemas, tree and ring ones (even if open).

For each network segment, you can connect up to 128 devices (reaching the physical limit of the used transceivers).
You must however consider the absorption of each module, where, using “high-consumption” devices, it could lower the number of connectable modules, or in any case be necessary to increase the section of the power cables. In this case it is possible to realize networks with more than one power supply provided, but always with the reference of the negative in common.

You can further increase the size of the network by using gateways galvanically isolated that, besides reducing the traffic on the network, allow a troubleshooting easier and more efficient.

As a physical medium of interconnection between modules (the Bus), you must use a suitable cable, characterized as follows:

• Insulation 400V or higher, which allows the Bus cable installation in cable ducts also containing the power cables.
• Shielding with aluminum foil and naked continuity wire (not to connect in most cases).
• Couple of not twisted 0.50mm2 or upper section wires, to convey the power supply of the modules.
• Couple of twisted 0.22mm2 or upper section wires, to convey the intercommunication data between the modules.

As method of communication for the exchange of data between the modules, it is used the CAN BUS protocol, version 2.0B at a speed of 16.6Kbit / sec.
This protocol, thanks to its safety features about errors monitoring, has become a “de-facto” standard in both the automotive and industry fields.
His CSMA-CA (Carrier Sense Multiple Access – Collision Avoidance) system allows data exchange between different nodes connected to the same Bus line, managing collisions according to the priority of the transmitted messages.
The moderately low speed of 16Kbit / sec allows to realize the good-sized modules networks while maintaining the error rate low on the line even without terminators and creating mixed structure networks.
Our communication system is “event driven” type, so the traffic on the bus is limited, even on large networks. To further limit the data congestion, there are the gateways that restrict the flow of messages between different segments of the Bus, selecting only the necessary ones and filtering the messages intended for local users.

The process of firmware structure contained in modules provides to:

• Process messages that arrive by the Bus line.
• Manage user interactions through the physical inputs of the module.
• Control the physical outputs according to the results of the process.
• Generate events (messages) on the Bus line according to the results of the process.

In any physical module are available some virtual entities, independent between them, called “objects”, which implement all four the above functions. Each object contains:

• Features:are all values that pass through the configuration procedure and that characterize the operation
  of the object, such as a switch-off time, a value of threshold etc. They can be Boolean values or word, float, setof.
  They are also part of the Features the states of operation of the object, such as, for example, relay on / off, dimmer 50%, etc.
• Endpoint (IN):are broadcast messages containers that the object reflects and according to the stimulus, changes the state of one of its features, for example a inverts the state of an output, or changes the adjustment value.
• Endpoint (OUT):are containers of broadcast messages that the object sends in response to a change of its
  conditions, for example to the stimulus of an input or the expiration of a timer. The message sent brings a value
  that will change the features of the receiving object.
• Inputs: are the physical inputs of the object (we find them on the hardware module). When stimulated, they change the internal features of the object.
• Outputs: are the physical outputs of the object (we find  them on the hardware module). They overturn outside the values of the features with which they are associated.