AN451 Datasheet, PDF (1/14 Pages) Silicon Laboratories – WIRELESS M-BUS SOFTWARE IMPLEMENTATION

AN451
WIRELESS M-BUS SOFTWARE IMPLEMENTATION
1. Introduction
This application note describes the Silicon Labs implementation of Wireless M-Bus using a Silicon Labs C8051
MCU and EZRadioPRO^®. Wireless M-bus is a European Standard for meter-reading applications using the
868 MHz frequency band.
1.1. Stack Layers
Wireless M-Bus uses the 3-layer IEC model, which is a subset of the 7-layer OSI model (see Figure 1).
Application
EN 13757-3
Data Link
EN 60870-5-2
MCU
app
mbus
phy
PHY
EN 13757-4
Si443x
Figure 1. Stack Layers
The Physical (PHY) layer is defined in EN 13757-4. The physical layer defines how the bits are encoded and
transmitted, the RF modem characteristics (chip rate, preamble, and synchronization word), and RF parameters
(modulation, center frequency, and frequency deviation).
The PHY layer is implemented using a combination of hardware and firmware. The EZRadioPRO performs all of
the RF and modem functions. The EZRadioPRO is used in FIFO mode with the packet handler. The MbusPhy.c
module provides SPI interface, encoding/decoding, block read/write, and packet handling and manages the
transceiver states.
The M-Bus Data link layer is implemented in the MbusLink.c module. The M-Bus Application Programming
interface consists of public functions that may be called from the application layer in the main thread. The
MbusLink module also implements the Data Link Layer. The Data link layer will format and copy data from the
application TX buffer to the MbusPhy TX buffer, adding the required headers and CRCs.
The Application layer itself is not part of the M-bus firmware. The application layer defines how a wide variety of
data is to be formatted for transmission. Most meters only need to transmit one or two types of data. Adding a large
amount of code to accommodate any kind of data to the meter would add unnecessary code and cost to the meter.
It might be feasible to implement a library or a header file with an exhaustive list of data types. However, most
metering customers know exactly what kind of data they need to transmit and can refer to the standard for
formatting details. A universal reader or sniffer might implement a complete set of application data types on the PC
GUI. For these reasons, the application layer is implemented using example applications for a meter and reader.
Rev. 0.1 2/10
Copyright © 2010 by Silicon Laboratories
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