KNX Stack Radio Frequency (KNX-RF)
Wireless data transmission within buildings
KNX-RF (radio frequency) is the wireless alternative in the KNX standard. In locations that are not suitable for either twisted pair cabling or Powerline technology, KNX-RF is used for wireless data transmission within a building.
Technical data for KNX-RF:
- Center frequency: 868.3 MHz
- Transmission power: 1-25 mW
- Duty cycle: < 1 %
- Modulation: FSK
- Coding: Manchester
- Chip rate: 32.768 cps
The KNX-RF wireless communication feature is manufacturer-independent and approved as an international standard, as is the entire KNX system. KNX-RF devices can be configured in Easy Mode, meaning that the system can be put into operation without requiring a PC or laptop. System Mode configuration using ETS® software is currently planned and will enable a setup of mixed installations with wireless and wired nodes.
The KNX-RF standard differentiates between unidirectional devices, which are only able to send data, and bidirectional devices, which also contain a receiver. Since unidirectional devices do not have to be in permanent receive mode, they use very little power and are therefore suitable for battery-driven sensors. Actuators must be bidirectional and are usually powered from the grid.
Features overview
- System software for KNX-RF devices
- Medium: Radio frequency (RF)
- Configuration modes: System mode, Easy mode
- Device models: 2010 und 2110
- Available for different microcontrollers
- Medium access over ISM Transceiver
- Source code in C
- Evaluation boards
- Software tools
- KNX certificate for the stack
Firmware architecture
The firmware includes more than just the communication stack: it provides a complete implementation of standardized device models
As does the KNX-RF standard, the implementation from Weinzierl Engineering differentiates between unidirectional and bidirectional devices. Unidirectional devices contain only the send function and a highly simplified communication stack. The software supports a power save mode to lengthen battery life. Because the unidirectional software has a code size of only a few Kbytes, very inexpensive controllers can be used.
The bidirectional implementation contains both a sender and a receiver. Although processing of received data is time-critical due to the relatively high data rate, it is still possible to detect and correct individual bit errors during reception. Consequently, communication quality is very high even when transmission conditions are unfavourable. Bidirectional devices contain a complete communication stack that also includes the link mechanism for putting the device into operation using the KNX Easy Push Button Mode.
Both the unidirectional and bidirectional implementations permit integration of the application software in the controller. The source code is modular in structure, fully documented and included in the scope of delivery.
Hardware
At its core, each device is equipped with a microcontroller that is responsible for bus communication and the application task. We currently support the following controller families for KNX-RF:
- Atmel ATmega
- Atmel ATxmega
- Atmel ARM7 (e.g. SAM7)
- Silicon Labs Si100x single-chip (8051 & Transceiver)
- Texas Instruments MSP430
The medium access to KNX-RF is realized for example on the:
- Silicon Labs Si4431 / Si4432
- Silicon Labs Si100x single-chip (8051 & Transceiver)
- Texas Instruments / Chipcon CC1101
- Texas Instruments / Chipcon TI CC1150
The simple design of the device keeps production costs at a minimum. The usage of alternative parts is of course possible as well. A selection of evaluation boards is available to give developers a head start.
The following hardware platforms are available for evaluating our stack implementation:
- KNX-RF development board (bidirectional)
- KNX-RF sensor board (unidirectional)
- KNX-RF actuator device (bidirectional)
- KNX-RF module without microcontroller
- KNX-RF module with microcontroller e.g. for KNX-RF UART
Tool environment
Reliable tools are absolutely essential for effective development and troubleshooting in existing systems. We have, therefore, extended our KNX analysis software, Net'n Node, for use with KNX-RF.
Net'n Node is a powerful bus monitor and analyzer to assist you during development and test. The program TraceMon displays additional debug information of the firmware.
Net'n Node can send and receive KNX-RF telegrams. The display is in cEMI format (part of the KNX standard). A USB interface is available for KNX-RF to access the medium.
Support
Included in the package is a developer workshop to help you getting started. We will advise you on your system architecture and give you full support with your development work. In addition we offer assistance for special issues concerning RF development like antenna matching.
Development services
If you are interested in individual solutions or complete device development, we offer application development services including hardware design, programming and system integration. With broad experience in the development of bus components and systems, we are looking forward to finding solutions tailored specifically to your requirements. Of course KNX product certification is included in our service.
If you have any questions on the development solution and our services, please do not hesitate to contact us.