KNX on LPC Microcontrollers

Document created by Fernanda Servin Employee on Apr 12, 2016Last modified by Brendon Slade on Sep 13, 2016
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The OM13043 kit described below is no longer available (the LPC1227 and LPC1100XL devices are still available). This material is provided for reference materials, but KNX software is still available from Weinzierl Engineering.

 

Building automation systems based on KNX communication protocols

 

Communication is becoming essential in complex buildings. For this reason, NXP cooperates with Weinzierl Engineering to offer dedicated components to realize KNX based systems. A professional version of the KNX system B stack is now available on LPC Microcontrollers to allow a jump start with KNX development.

NXP_OM13042.jpg

 

System notes

LPC1100XL and LPC1200 series microcontrollers:

  • Based on the highly energy-efficient ARM® Cortex™-M0 processor
  • Dramatically lower the cost per KNX node in home and building automation networks
  • Cortex-M0 architecture ideally suited for low-complexity end nodes
  • Include up to 128 KB Flash and 8 KB SRAM, and offer highly configurable peripherals
  • Can be powered directly from the DC-DC converter of the KNX twisted-pair transceivers, making bus-powered devices easy to implement
  • With performance levels up to 45 DMIPS, a single MCU delivers the resources required to run a KNX System B stack (up to 65535 nodes), with enough bandwidth available for the end application
  • Reduced time to market – full professional stack available from partners with flexible license models
  • A certified implementation of the KNX System B is available for the LPC1200 from Weinzierl Engineering 

 

Implementation example (OM13042 demo board):

  • Available with the NXP LPC1227 microcontroller and ON Semiconductor’s NCN5120 transceiver, suitable for use in KNX twisted pair networks (KNX TP1-256)
  • Specifically designed to simplify design process with a ready-to-implement, energy-efficient KNX TP solution for applications such as lighting switches and control, HVAC control, shutters and occupancy detection
  • Improves power efficiency, reduces development costs, accelerates time to market for KNX applications on ARM Cortex-M0
  • Application Note AN11231 is available here

om13042 schematic_0.preview.JPG

 

More information on KNX:  www.knx.org

 

KNX TP Stack System B from Weinzierl Engineering - The new dimension of KNX development

Each KNX device is based on a device model, that specifies both the management procedure (that is, how the device is configured via the bus) and identifies the resources available to the device (for example, the maximum size of the connection table).

KnxStackTP_SystemB_32Bit_small.gif

System B (mask version 07B0) is a new device model that has been defined specifically for the implementation of complex KNX devices. The main advantage lies in the number of available communication objects. While previous devices models were limited to 255 objects or less, System B theoretically permits up to 65,535 communication objects. To achieve this, the formats of the communication tables (group address, association and group object tables) have been redefined in the KNX specification for System B.

 

System B devices can update their communication objects at system startup. This function is called Read-On-Init and can be activated individually for each object. Once the application is started the system software sends group read-value services independent from the application task. These services are scheduled by the stack to ensure that the bus is not excessively loaded at startup.

 

System B also offers a greatly increased address space. The configuration data (application, parameters and tables) can be loaded into a range of up to 1 MB (20-bit addressing) via the bus (using memory services). To access system parameters, additional properties in the interface objects of the system have been introduced.

 

System B is supported by the ETS manufacturer tool MT4, by ETS3 andETS4.

 

Implementation for optimal performance

Weinzierl Engineering as a KNX system supplier offers a new implementation for KNX System B, specifically targeted at complex devices with a 32-bit architecture like the Cortex M0 from NXP. It includes a complete implementation of the specification and is optimized to ensure high performance for all application sizes.

 

A major consideration in the development of System B is the timely (real-time) processing of the large association table, which contains the assignment of group addresses to the communication objects and vice versa. It is loaded by ETS and is not sorted. For a table length of more than a thousand entries, linear search algorithms are not effective and therefore additional look-up tables have been introduced that allow quick access via indices. The processing of the communication objects has also been accelerated and a linear search through all objects is avoided with the use of additional buffers.

 

Although these design features may require additional memory, they facilitate low CPU clock speeds. Higher performance is achieved at the same frequency with than with previous implementations with considerably reduced KNX resources.

 

The System B implementation from Weinzierl Engineering uses a virtual address space that is resolved at the driver level and mapped to the corresponding physical storage areas. This means that applications are easily ported to different platforms.

 

KNX_FirmwareExtendedv8_small.jpg

As for all Weinzierl's stack implementations, the focus is to ensure ease of application development. The application interface has been largely maintained and is accessible via comprehensive API functions. It is possible to implement either internal or external applications. An internal application is bundled together with the stack in the device and the ETS simply has to load the parameters and tables, which ensures quick download times. An external application is loaded by the ETS along with the parameters and tables.

 

The stack also supports additional interface objects (user properties). These objects can be used, for example, to set device parameters using point-to-point communication on the bus. ETS parameters can also be realized with Properties.

 

For the creation of the product data base with ETS MT4 (Manufacturer Tool) our bus monitor and KNX development tool Net'n Node has been extended with a new export function. After importing the data of the software project it directly generates an XML file that contains all the storage areas, load controls and binary application data. This XML file can be imported directly into the MT4 solution.

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