Silicon Laboratories Wireless M-Bus-EK User manual

Rev. 0.1 2/10 Copyright © 2010 by Silicon Laboratories Wireless M-Bus-EK
Wireless M-Bus-EK
WIRELESS M-BUS DEMONSTRATION KIT USER’SGUIDE
1. Kit Contents
The Wireless M-Bus Demonstration Kit contains the following items:
Wireless M-Bus Demonstration Board
3.6 V Lithium battery
USB cable
AC to DC power adapter
868 MHz antenna
2. Introduction
The purpose of the Wireless M-Bus Demonstration Kit is to demonstrate a low-power meter application using the
Wireless M-Bus stack. The demonstration has three basic system components:
Wireless M-Bus Meter Demonstration Kit (Meter)
Monitor
PC Application
The Wireless M-Bus Meter Demonstration Kit performs the basic metering functions. It will either count pulses or
measure the temperature. The Meter will also periodically wake up and transmit the data using the Wireless M-Bus
protocol.
The Monitor measures and displays the current consumption of the Meter. The Monitor also communicates with the
PC application and configures the Meter over a UART connection.
The Wireless M-Bus Demonstration board is shown in Figure 1. The right half of the board implements the Meter,
and the left half of the board implements the Monitor.
Figure 1. Wireless M-Bus Demonstration Board

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3. Hardware Overview
The Wireless M-Bus Demo board has two sections. The Wireless M-Bus meter section is on the right half as
shown in Figure 2.
Figure 2. Meter Section
The Wireless M-Bus meter section includes the following components.
C8051F930 Low-Power Microcontroller
Si4431 EZRadioPRO®Transceiver
CP2400 LCD Driver
The C8051F930 is well suited for Low-Power Metering solutions. This MCU includes 64 k of Flash and 4 k of RAM,
which is sufficient for the Wireless M-Bus stack and a large application. The C8051F930 has a very low-power
Sleep mode. The current consumption in Sleep mode is only 50 nA. The MCU also has a 32.768 kHz
SmaRTClockTM. The MCU SmaRTClockTM is used for all timing functions in the low-power meter.
The Si4431 EZRadioPRO®transceiver provides +13 dB of output power. This is the highest power permitted in the
868 MHz band used by the Wireless M-Bus Standard. The RF layout is matched for 868 MHz. The Si4431 is
placed in Shutdown mode when the radio is not in use. The current draw in shutdown mode is only 15 nA.
The CP2400 LCD driver features an SPI interface and can drive displays with up to 128 segments and four
backplanes. The Wireless M-Bus meter section uses a static four-digit display for the lowest possible power
consumption. The Meter Display is used to display either pulse count or Temperature. The Monitor Section is
shown in Figure 3.
C8051F930
CP2400
Si4431

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Figure 3. Monitor Section
The monitor section includes the following components:
C8051F342 USB microcontroller
CP2400 LCD driver
The C8051F342 microcontroller is used to monitor the meter current consumption, display the current consumption
on the eight-digit alphanumeric display, and communicate over USB with the PC applications on the PC host. The
discrete current amplifier and integrator are used with the internal comparator and timer to calculate the average
current consumption.
A second CP2400 is used to drive the monitor display. The monitor display is an alphanumeric display with eight
14-segment characters. The monitor display is normally used to display average current consumption. Pressing
the Mode button will alternately display the elapsed time or output pulse frequency.
Three pin headers are provided for different power options. The Wireless M-Bus demo board may be powered from
a USB, a wall adapter, or a 3.6 V long-life Lithium battery. The meter section can be powered from the battery while
the monitor section is powered from USB or wall power.
C8051F342
CP2400

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4. Software Overview
The software system diagram is shown in Figure 4. The meter application firmware runs on the C8051F930 and is
written on top of the Wireless M-Bus stack. The meter application firmware measures the temperature or counts
the number of pulses and is configured over the UART interface by the monitor application firmware.
The monitor application firmware runs on the C8051F342. The monitor application uses the USBXpress®library
and embedded API.
Figure 4. Software System Diagram
USBXpress
Wireless Meter
Bus Demo
Monitor App
EZRadioPRO
‘F930
PC
USB
WMBus Stack
Meter App
‘F342
CP2400 CP2400
SPI
UART
SPI

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5. Install Wireless Meter-Bus Software
Download the Wireless M-Bus demo software from the Silicon Labs web site:
www.silabs.com/wirelessmbus
The Wireless Meter-Bus demo requires Windows 2000®, XP®, Server2003®, Vista®, or Windows 7®. Download
the software, unzip it, and run the installer executable.
6. Install USBXpress Driver
The Wireless M-Bus PC software uses the USBXpress API and requires the USBXpress driver. Download and
install the USBXpress driver before connecting the Wireless M-Bus board to the computer via USB. There is no
cause for concern if you have already connected the Wireless M-Bus demo board to the PC. Disconnect the
Wireless M-Bus demo board, and proceed with the USBXpress installation.
Download and install the USBXpress development kit for windows from the Silicon Labs website:
www.silabs.com/USBxpress
Unzip the file and run the executable program. When prompted, check the “Install USBXpress Drivers” checkbox to
install the USBXpress Drivers immediately. If you miss this step, the USBXpress driver can be installed later by
running the driver installer. The following path is the USBXpress driver installer default location:
C:\SiLabs\MCU\USBXpress\Driver\USBXpressInstaller.exe
Configure the shorting blocks before connecting the USB cable as explained in “7. Hardware Setup”.

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7. Hardware Setup
Please install the USBXpress drivers before connecting the Wireless M-Bus demo board to the PC (see “6. Install
USBXpress Driver”).
The Wireless M-Bus Demo Board has three headers on the left side of the board to configure the C8051F342 and
C8051F930 power sources.
To configure both MCUs to operate from USB power, configure the headers as shown in Figure 5.
Configure shorting blocks to short pins 2 and 3 on J10.
Remove shorting block on J11.
Configure shorting blocks to short pins 1 and 2 of J12.
Figure 5. USB Power Configuration
The headers in the middle of the board provide options for measuring the current of the C8051F930 MCU, Si4431
EZRadioPRO, and CP2400 LCD Controller.
To configure the Monitor circuit to include the MCU and radio current, install the headers as shown inFigure 5.
Short pins 1 and 2 on J5 with a shorting block.
Remove shorting block on J6 to enable 1 resistor.
Short pins 2 and 3 on J7 to enable MCU current measurement.
Short pins 2 and 3 on J8 to enable radio current measurement.
Short pins 1 and 2 on J9 to disable LCD current measurement.
Short pins 2 and 3 on J13 to power the CP2400 from the meter supply.
After configuring the headers, connect one end of the USB cable to the Wireless M-Bus demo Board and the other
end to the PC. The first time the Wireless M-Bus demo board is connected to the computer, the Found New
Hardware wizard will indicate “Found New Hardware - USBXpress Device”. If the Found New Hardware wizard
fails to correctly identify the USBXpress device, ensure that the USBXpress drivers are installed correctly as
explained in “6. Install USBXpress Driver”.
J2
J1
SW2 SW1
J8
J7
J9
J10
J11
J12
J6
J5
J13
SW3 F342
U4
CP2400
U5
CP2400
U3
F930
U2
U1
SILICON LABS
www.silabs.com
J4 J3
Monitor Meter Wireless M-Bus Demo Board
D1 D2 D3 D4
DIS2 DIS1
ANT1

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8. PC Application
After installation, the Wireless M-Bus PC application is located in the following default directory:
C:\SiLabs\MCU\Wireless_Meter_Bus\Software\MBusDemo.exe
The initial screen is shown in Figure 6.
Figure 6. Wireless M-Bus Demo PC Application
If the M-Bus demo hardware is connected to the PC and the USBXpress driver has been installed, the demo board
serial number should be displayed in the Device drop-down menu. If the serial number is not displayed, perform
the following steps:
1. Check that the USBXpress driver has been installed.
2. Check that the shorting block configuration is set up according to the hardware setup.
3. Check the USB connection to your PC.
4. Check that the LCD displays are active.
If the LCD displays are not active, this indicates that the board is not powered.

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The power consumption of the meter depends on the parameter settings. The PC application allows the following
parameters to be set:
Transmit Period
Data Field Length
M-Bus Mode
Transceiver Mode
Data Select
Pulse Frequency
Encryption
LCD Enabled
8.1. Transmit Period
The transmit period can be set for 1 second to 3600 seconds (5 minutes). The C8051F930 MCU will sleep for this
period with the Si4431 EZRadioPRO in shut-down. Then, it will wake up, take a measurement, and send the data.
The Transmit period has a large effect on the power consumption. A long transmit period is necessary to achieve
multi-year battery life.
8.2. Data Field Length
The data field length sets the length of the application payload in the M-Bus packet. The minimum length is 2,
including the required CI byte. The maximum is 100 bytes. If AES encryption is enabled, this field must be a
multiple of 16.
8.3. M-Bus Mode
The following menus can be used to select the M-Bus mode:
Mode S: 32,768 cps Manchester encoding
Mode SL: same as above with a very long preamble
Mode T: 100 kcps, three-out-of-six encoding
Mode R: 4800 cps, Manchester encoding
Mode T provides the highest data rate and gives the lowest power consumption. The current consumption of Mode
SL with the long preamble is slightly higher than Mode S. The long preamble is not necessary for the Si4431
EZRadioPRO. Power consumption is the highest using Mode R. Sending a long packet using Mode R may take
hundreds of milliseconds. Mode T2, Mode S2, and Mode R2 may be selected by choosing TX and RX in the
Transceiver mode menu. According to the specification, Mode R should always use TX and RX. For additional
information about M-Bus modes, refer to “AN451: Wireless M-Bus Software Implementation” and EN 13757-4.
8.4. Transceiver Mode
The Wireless M-Bus demo PC application provides two transceiver modes:
TX
TX and RX
If the TX only mode is selected, the meter will sleep for the transmit period, wake up, and transmit its data. If the TX
and RX mode is selected, the meter will wake up and send an access demand message. If the access demand
message is acknowledged, the meter will send its data to the other device.
When a meter reader (Other) device is present, the current consumption of the two-way communication is highest.
Because there is overhead associated with the two-way data transfer. If the meter reader (Other) is not present, the
two-way meter only needs to send the access demand message and wait for the response time. Still, the response
time is long compared to the message length; so, the one-way communication usually provides the lowest power
consumption.

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8.5. Data Select
The options for the Data Select menu are:
Pulse
Temperature
None
The selected data is displayed on the LCD and transmitted in the data payload.
The Pulse option provides a pulse counter. The C8051F342 acts as a virtual water or gas meter. The C8051F930
will wake up on each rising and falling edge and count the number of pulses. The pulse rate is programmable.
The Temperature sensor uses the onboard temperature sensor on the C8051F930.
The power consumption will be higher using the pulse counter. This is because the MCU must wake up often to
count the number of pulses. Using the temperature sensor, the current consumption is less because the
temperature is only measured before each transmission.
8.6. Pulse Frequency
When pulse data is selected, the pulse frequency is programmable from 0.1 to 10 Hz. The 0.1 Hz provides one
pulse every ten seconds.
8.7. Encryption
The AES encryption option will encrypt the data before sending. The demo uses the AES 128 block cipher.
Ecrypting the data takes some extra time and results in higher power consumption. The encryption time will be
higher for longer data lengths.
Since the demo uses the basic AES128 block cypher, the data size must be a multiple of 16. The transmission data
should be padded with zeros. Other encryption modes might accommodate an arbitrary length.
8.8. LCD enabled
The LCD display takes power to operate and update. The three-pin header, J9, may be configured to exclude the
LCD current from the measurement. However, the C8051F930 is still updating the LCD display. Disabling the LCD
turns off the Meter display, and the MCU will not have to update the display. This decreases the time that the
C8051F930 has to be awake and lowers power consumption.
Normally, the CP2400 is powered from the same voltage supply as the C8051F930. However, the LCD current is
so low that the CP2400 may be powered from an I/O pin of the C8051F930. The LCD current may be further
decreased by configuring J13 with a shorting block on Pins 1 and 2. This powers the CP2400 from an C8051F930
I/O pin and further lowers the power consumption when the LCD is disabled.

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9. Wireless M-Bus Stack
The source code for the Wireless M-Bus stack is available as a separate download from the M-Bus web page:
www.silabs.com/wirelessmbus
Additional information on the Wireless M-Bus stack may be found in the following application notes:
“AN451: Wireless M-Bus Software Implementation”
“AN452: Wireless M-Bus Stack Programmers Guide”
The source code may only be used in accordance with the terms in the click-through license agreement. The
source may only be used with a Silicon Labs MCU and Silicon Labs radio product.
The Wireless M-Bus source code supports two development platforms: The Si4431 EzRadioPRO development
platform using the C8051F930 MCU and the Si1000 integrated MCU/EZRadioPRO platform.
The M-Bus demo board is intended as a demo only. It is not supported as a development platform.