wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

KNX 42-11
42.5 Devices
Various building blocks exist for developing KNX compatible devices. Different transceivers are
required depending on the transmission medium. For TP1, four different transceiver solutions allow
optimization of the KNX device design in accordance with the area of application. A transceiver circuit
constructed from discrete components offers low-cost bus access, but requires high certification effort.
The use of the FZE 1065 transceiver IC with transformer coupling and bit interface allows a highly resistant
solution, while the FZE 1066 transceiver with direct bus coupling enables a resistant and miniaturized
solution. Both transceiver ICs offer a bit interface and allow implementing a certified physical layer
with minimum effort. Finally, the TP-UART IC is a transceiver with direct bus coupling and a UART
host interface. It allows certified and miniaturized bus access with relaxed timing requirements on the
microcontroller, as it handles most of the KNX TP1 DL. For the PL110 medium, only a single type of
transceiver ASIC is available. The use of the RF and IP media does not require hardware that is specifically
designed for KNX.
To further ease system development and certification, KNX defines standardized communication
modules (i.e., bus attachment units, BAUs) such as the bus coupling unit (BCU), the bus interface module
(BIM), or the powerline interface module (PIM), which provide an implementation of the complete
network stack and application environment. They can host simple user applications, supporting the use
of GOs in a way similar to local variables. BIMs/PIMs are soldered or detachable communication modules
that are directly attached to the main device circuit board whereas BCUs are equipped with housing
and shielding against electromagnetic interference.
Most KNX devices come either in rail-mount housings for mounting in distribution boxes or as flushmount
devices. Flush-mount end devices based on BCUs are typically split into two parts, the communication
module (i.e., BCU) and the application module. Both are connected via the standardized
physical external interface (PEI), which can be configured in a number of ways. Simple application modules
such as wall switches may use it for parallel digital I/O or as inputs to the BCU A/D converter. More
complex user applications requiring the use of a separate microprocessor may use the PEI for high-level
access to the network stack via EMI wrapped in an asynchronous serial protocol (BCU 1 devices use
a protocol with proprietary hardware handshaking, while the protocol supported by BCU 2 devices is
based on FT1.2 as specified in IEC 60870-5).
Different generations of TP1 communication modules exist. The traditional BCU 1, BIM M111,
and BIM M115 modules feature a Motorola 68HC05B6 or compatible type microcontroller running
at 2.MHz with 176 bytes RAM, 256 bytes EEPROM, and 5936 bytes ROM. BCU 2 and BIM M113 use a
68HC05BE12 microcontroller running at 2.4576.MHz. They have 384 bytes RAM, 991 bytes EEPROM,
and 11904 bytes ROM. Most of the RAM and ROM are occupied by the system software. To overcome
the severe performance limitations of these out-dated platforms, a new generation of BIMs has been
developed. They are based on the NEC 78K0/Kx2 microcontroller and offer from 8 up to 48.kB flash
memory. Additionally, a far more comfortable software development toolchain (including a C compiler
and debugger) is available for this new platform. For PL110, 68HC05B16 microcontroller based BAUs
(e.g., PIMs) exist that are quite similar to the 68HC05B6 series but feature larger ROM and RAM and a
clock frequency of 4.MHz.
Apart from these standardized BAUs, various other KNX certified interface modules exist. For example,
so-called serial interface modules (SIMs) are available, which can be directly soldered to printed
circuit boards in a way similar to BIMs. They contain the complete communication stack and the application
can interface with the KNX network using a simple, proprietary serial protocol. Complete software
stacks for several microcontroller families (e.g., Atmel ATmega and ARM7, Texas Instruments
MSP430, NEC 78K0) can also be obtained from various vendors.
© 2011 by Taylor and Francis Group, LLC