Building automation with KNX and BIMs

Developing and building smart homes have become trendy and cool in the last decades, as problems like energy efficiency and aging society were considered more and more serious.

Different standards have been defined in order to create a basis for the building automation industry. A widely spread one is called KNX (Konnex).

KNX is a standardized (EN 50090, ISO/IEC 14543), OSI-based network communications protocol for intelligent buildings. KNX is the successor to, and convergence of, three previous standards: the European Home Systems Protocol (EHS), BatiBUS, and the European Installation Bus (EIB or Instabus).

The standard is based on the communication stack of EIB but enlarged with the physical layers, configuration modes and application experience of BatiBUS and EHS.

KNX is designed to be independent of any particular hardware platform. A KNX Device Network can be controlled by anything from an 8-bit microcontroller to a PC, according to the needs of a particular implementation. The most common form of installation is over twisted pair medium.” (Wikipedia)

The nice thing is, that a new appliance may be developed from scratch, and integrated into an already functional KNX-based smart building. No need to buy certain products/technologies from specified companies, the newly developed system only needs to be able to communicate with other devices via the KNX bus. It does not matter which microcontroller is used for the development, though, the developer must implement a communication layer which conforms to the KNX-standard.

There is also another possibility, namely using BIMs: KNX Bus Interface Modules.  These “bus interface modules are printed circuit boards consisting of the chipsets (TP-UART + KNX microcontroller) mounted with all necessary components”. The BIM modules “contain the BCU 2.5 system software compliant to the KNX specification.” (Siemens Building Technologies)

I’ve googled a bit around, but I did not find any other BIM providers but Siemens.The newest bus interface modules family developed by Siemens Building Technologies is called BIM M13x, and has 4 family members: M130, M131, M132, M135. (Actually, the only difference between M130 and M135 is that M135 may be used at extended temperature ranges.)

“The BIM M13x series is based on the NEC78K0/Kx2 microcontroller family providing state of the art flash technology”. The family members basically differ from each other in the available Flash and RAM memory sizes that can be used by the application program. (Refer to the Siemens webpage for the exact specifications)

If the BIM modules are used to develop new KNX-appliances, the system developer can invest more time in creating the application specific hardware and software. He does not need to take care about the communication layer, as the communication with other KNX-devices can be easily implemented using the API, which calls the functions of the already installed firmware. (BCU 2.5)

As it is observable from the picture, the pins of the KNX-microcontroller are wired to a socket, so that the application specific hardware can be easily connected. The application program can be downloaded to the BIM, by connecting it to the KNX-bus, and using the BIM-Tools for program download.

Available development toolpackage

The company Opternus GmbH offers not only the BIM M13x modules, but also a “a modern tool chain including debug tools leading to shorter development times.

This toolpackage includes following items:

  • Evaluation Board with BIM M132 functionality (largest family member) – most reduced memory restrictions
  • NEC Minicube development platform for downloading the firmware and for online debugging (Needed software is included)
  • IAR Embedded Workbench – The size limited version of the development environment
  • BIM Tools – tool for downloading the application program

Although, the related documentation is also included in the package, it took me some time to figure out how all these tools work. In a further article I will explain how I made the toolchain work.


The sources of the pictures and citations are:

(The article has been first published on the 31st of March 2012 on an older website of the author)

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