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Implementation Aspects for KNX TP Devices

One will be confronted with a several technical terms like "BIM", "BCU", "SIM", "TPUART", "chipset" and "communication stack" when exploring the market. These terms represent the different possibilities on how to develop a KNX TP Device.   

BCU "Bus coupling units"

These are system devices which include the KNX coupling circuitry, a microprocessor and are delivered with housing. The device developer only needs to develop the application module, the application hardware and software.   

BIM "Bus Interface Modules" 

They are basically built up like the inside of a BCU with additional I/O ports. BIMs are sold as modules which can be soldered directly to the circuit board. There are versions available with 8kbyte and 48 kbyte flash memory for the application software. The software development takes place with a development environment consisting of "Evaluation board", "On-Chip Debug Emulator" and C-Compiler.   

SIM "Serial Interface Modules"

They contain the complete communication system with applications. The application hardware and software is coupled with the communication part via serial interface. SIMs are sold as modules which are soldered directly to the circuit board.   

BAOS "Bus Access and Object Server"

The BAOS Module is both a KNX interface on Telegram level (KNX Link Layer) as on Datapoint level (KNX Application Layer). The telegram format is FT1.2 conform. An optimized serial protocol is available for the communication on Data- Point level.   


Chipsets of BIMs are offered to circumvent the mechanical constraints of BIMs. There is no difference between BIMs and chipsets with regard to the software.   


The TPUART only contains the coupling to KNX. The communication software is supplied by a micro-controller. The TPUART was developed to relieve the micro controller of the bit coding and decoding duty on the one hand and to allow the coupling to KNX through different micro-controllers on the other hand.   

Communication Stack 

To develop a KNX device with the TPUART, a communication stack is required. This kinds of coupling is the most effective, flexible and low-cost way of developing a KNX device. To eliminate the need for the developer to familiarize themselves with details of the KNX communication, KNX system vendors offer the KNX communication stack. The coupling to KNX is performed through external KNX coupler like TPUART, FZE1066. The KNX communication stack offers additional interfaces to program the actual application.   

What is the right solution? 

The modules (BIM, SIM BAOS) are recommended in case of smaller production quantities. They offer low development - and certification costs and are ideal to start with KNX development. If the available space becomes insufficient or the production quantities increase, then the chipsets are an interesting alternative. The initial costs are just a little higher as compared to BIM. TPUART is the most popular solution in case of large production quantities. The advantage of TPUART is the low cost per unit, but has on the other hand the highest development- and certification costs. It can in particular cases also be useful to opt for a Bit Transceiver (FZE1066).