dm00233038

AN4772
Application note
wM-Bus (2013) firmware stack overview
Introduction
M-Bus (meter bus) is a common automatic meter reader (AMR) standard for remote energy meter
reading in compliance with European standard (EN 13757-2 physical and link layer and EN 13757-3
application layer). M-Bus is also compliant with the European Standard EN 1434 on heat meters.
The M-Bus interface is based on the very cost effective two-wire, twist cable transmission, and is
compatible with all network topologies (linear, star, etc.) except ring networks. When queried, meters
send their data to a concentrator from which the data can be read locally or remotely.
Wireless M-Bus is the radio variant of M-Bus for automatic meter reading at sub-1-GHz radio
frequencies. While European standard EN13757-3:2013 for the application layer remains the same as
M-Bus, the applicable physical and link layer European standard becomes EN13757-4:2013 Wireless
meter readout, as well as ETSI EN 300 220 v2.3.1 for short range radio equipment.
The Wireless M-Bus firmware stack is based on EN 13757-4:2013 (Communication systems for meters
and remote reading of meters — Part 4: Wireless meter readout (Radio meter reading for operation in
SRD bands)). This European Standard specifies the required physical and link layer parameters for
systems using radio to read remote meters, focusing primarily on the use of unlicensed, short range
device (SRD) telemetry bands. The standard encompasses systems for walk-by, drive-by and fixed
installations.
Several different modes of operation are defined for meter communication, with specific parameters
governing only the operational and technical requirements of these differing modes, leaving the bulk of
common parameters to facilitate common software and architecture components.
Mode nomenclature consists of a letter and a number. The letter specifies the mode type and the
number specifies whether the mode supports unidirectional (1) or bidirectional (2) data transfer.
Figure 1: Basic Wireless M-Bus architecture
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Contents
AN4772
Contents
1
Definitions, acronyms and abbreviations ...................................... 7
2
Hardware platform ........................................................................... 8
2.1
SPIRIT1 ............................................................................................ 8
2.1.1
2.2
ST’s ultra-low power EnergyLite™ MCU family................................. 9
2.2.1
3
4.2
3.1.1
Stationary mode (S Mode) ............................................................... 11
3.1.2
Frequent transmit mode (T Mode) .................................................... 11
3.1.3
Frequent receive mode (R2 Mode) .................................................. 11
3.1.4
Narrowband VHF mode (N-Mode) ................................................... 11
3.1.5
Frequent receive and transmit mode (F-Mode) ................................ 11
3.1.6
Compact Mode (C-Mode) ................................................................. 12
Frame structure ............................................................................... 13
4.1.1
Preamble .......................................................................................... 13
4.1.2
Payload ............................................................................................. 13
4.1.3
Postamble (trailer) ............................................................................ 13
Physical layer files........................................................................... 13
Wireless M-Bus link layer ............................................................. 14
5.1
Data link layer functions .................................................................. 14
5.2
Link layer specification .................................................................... 14
5.3
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wM-Bus modes ............................................................................... 10
Wireless M-Bus physical layer ..................................................... 13
4.1
5
STM32L function: ............................................................................... 9
Wireless M-Bus protocol overview .............................................. 10
3.1
4
SPIRIT1 function: ............................................................................... 8
5.2.1
Frame format A................................................................................. 14
5.2.2
Frame format B................................................................................. 14
5.2.3
The L-field ......................................................................................... 15
5.2.4
The C-Field ....................................................................................... 15
5.2.5
Manufacturer ID (M-field).................................................................. 15
5.2.6
Address (A-field) ............................................................................... 15
5.2.7
CI-field .............................................................................................. 16
5.2.8
Data field .......................................................................................... 16
5.2.9
Cyclic redundancy check (CRC-field)............................................... 16
Link layer firmware implementation ................................................. 16
5.3.1
File description ................................................................................. 16
5.3.2
State machine flow structure ............................................................ 16
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Contents
5.4
6
Application layer dependent parameters ......................................... 18
Revision history ............................................................................ 20
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List of tables
AN4772
List of tables
Table 1: Acronyms and abbreviations ........................................................................................................ 7
Table 2: wM-Bus modes ........................................................................................................................... 10
Table 3: First block (format A) .................................................................................................................. 14
Table 4: Second block (format A) ............................................................................................................. 14
Table 5: Optional block (format A) ............................................................................................................ 14
Table 6: First block (format B) .................................................................................................................. 15
Table 7: Second block (format B) ............................................................................................................. 15
Table 8: Optional block (format B) ............................................................................................................ 15
Table 9: State machine table for meters ................................................................................................... 17
Table 10: State machine table for other devices ...................................................................................... 18
Table 11: Document revision history ........................................................................................................ 20
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List of figures
List of figures
Figure 1: Basic Wireless M-Bus architecture .............................................................................................. 1
Figure 2: Typical application scenario ........................................................................................................ 6
Figure 3: Firmware architecture .................................................................................................................. 6
Figure 4: Application layers ........................................................................................................................ 8
Figure 5: Wireless M-Bus physical structure. ........................................................................................... 13
Figure 6: Physical layer directory structure............................................................................................... 13
Figure 7: The C-Field ................................................................................................................................ 15
Figure 8: Link layer directory structure ..................................................................................................... 16
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The standard defines the communication protocol between remote meters and mobile readout devices,
stationary receivers, data collectors etc.
Figure 2: Typical application scenario
This document describes the wM-Bus physical (Phy) and link layers of the Wireless M-Bus firmware
stack application, developed by STMicroelectronics in compliance with applicable European standards.
Figure 3: Firmware architecture
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AN4772
1
Definitions, acronyms and abbreviations
Definitions, acronyms and abbreviations
Meters: devices that request/send data to the other devices via the wM-Bus standard.
Other devices: usually concentrator devices which exchange the information with meters.
They are the mobile readout devices.
Firmware: the firmware referred to in this document is developed and tested on the Spirit1
+ STEVAL-IKR001Vx board and is compliant with wM-Bus 2013 standard (NEN-EN 137573:2013 & NEN-EN 13757-4:2013).
Table 1: Acronyms and abbreviations
Acronym
Description
ACC-DMD
Access-Demand
ACC-NR
Access-No Reply
ACK
Acknowledgement
AMR
Automatic Meter Reading
CNF-IR
Confirm Installation Request
MHz
Mega Hertz
REQ-UD
Request User Data(Class1/2)
RSP-UD
Respond User Data
SND-IR
Send Installation Request
SND-NKE
Send Link Reset
SND-UD
Send User Data
USB
Universal Serial Bus
wM-Bus
Wireless Meter Bus
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Hardware platform
2
Hardware platform
ST’s Wireless M-Bus firmware stack application is based on its proprietary dual chip
platform: the new SPIRIT1 RF Sub-1 GHz transceiver and the STM32L15 ultra-low-power
ARM Cortex-M3 microcontroller.
Figure 4: Application layers
2.1
SPIRIT1
SPIRIT1 is a very low power, high performance RF transceiver, ideal for RF wireless
applications in the sub-1-GHz band. It is designed to operate at 169, 315, 433, 868, and
915 MHz and supports 2-FSK, GFSK, MSK, OOK, and ASK modulations. The air data rate
is programmable from 1 to 500 kbps, depending on the selected modulation.
Its integrated SMPS allows very low power consumption:

9 mA in Rx and 21 mA in Tx mode at +11 dBm.
Furthermore, it uses a very small number of discrete external components and integrates a
configurable baseband modem for data management, modulation and demodulation. Data
can be managed in a proprietary, fully programmable packet format as well as the M-Bus
standard compliant format (all performance classes).
The SPIRIT1 provides native hardware support for the low level wM-Bus Phy protocol.
2.1.1
SPIRIT1 function:




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wM-Bus Modes
Header, Sync and trailer fields
Manchester/3-out-of-6-encoding
Sync detection
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2.2
Hardware platform
ST’s ultra-low power EnergyLite™ MCU family
Gas, water and heat meters with wM-Bus technologies are usually battery powered devices
that need to be highly efficient to preserve battery life.
The 8-bit (STM8L) and 32-bit (STM32L) EnergyLite™ family of MCUs combines high
performance and ultra-low power, offering specific features for ultra-low power applications
such as advanced ultra-low power modes and optimized dynamic run consumption, as well
as special safety features.
The ultra-low-power EnergyLite platform, based on STMicroelectronics’ 130 nm ultra-lowleakage process technology, provides a common technology, design and peripheral
framework across the product range.
The ARM® Cortex™-M3-based STM32 L1 series extends the ultra-low power concept
without compromising performance, offering a wide assortment of features, memory sizes
and package pin quantities. The range covers 32 to 384 Kbytes Flash memory (with up to
48 Kbytes of RAM and 12 Kbytes of true embedded EEPROM) and 48 to 144 pins.
This innovative architecture, with voltage scaling and an ultra-low-power MSI oscillator,
gives your design more performance for a very low power budget. The generous suite of
embedded peripherals, including USB, LCD interface, OpAmp, comparator, ADC with fast
on/off mode, DAC, capacitive touch and AES renders the STM32 L1 series an expandable
platform able to fit all your requirements.
2.2.1
STM32L function:



wM-Bus application layer

wireless M-Bus application layer partially implementing EN13757-3.
wM-Bus link layer

MAC packet and CRC handling

encryption/ decryption initiate/read.
wM-Bus Phy

init Phy for wM-Bus

interrupt services
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Wireless M-Bus protocol overview
3
Wireless M-Bus protocol overview
Some of the salient features of the Wireless M-Bus standard are:





support for unidirectional and bidirectional communication between meters and other
devices
support for different of communication modes (S, T, R, N (Except N2g), C and F),
depending upon the requirement of the application
support for AES-128 encryption for data security
operates both in the license-free ISM and SRD frequency bands at 169, 315, 433,
868, and 915 MHz
provision for indicating faults and alarms.
More details can be found in the EN 13757-4 standard.
For the physical layer, the EN 13757-4 standard also specifies various performance
classes depending on the maximum power to be transmitted and lowest receiver sensitivity
that the meter provides.
The data link layer of the EN 13757-4 standard supports two different frame formats: A and
B. In a standard Wireless M-Bus received frame, the data link layer immediately follows the
preamble chip sequence, carrying link layer data plus optional application layer payload
information. For C, F and modes, the frame format can be determined from the pattern of
the preamble chip sequence. The Wireless M-Bus standard allows for the encryption of the
payload data using optimized encryption modes like AES 128 CBC.
3.1
wM-Bus modes
The following table summarizes the various modes supported by STMicroelectronics wMBus stack.
Table 2: wM-Bus modes
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Mode
Communication
Frequency
band
S1
Unidirectional
868 MHz
Stationary mode: metering devices send their data
several times a day. The data collector may be a battery
operated device and optimized for stationary operation.
S1-m
Unidirectional
868 MHz
Same as S1, but the data collector is a mobile receiver.
S2
Bidirectional
868 MHz
Bidirectional version of S1.
T1
Unidirectional
868 MHz
In the frequent transmit mode, meters send the data
every few seconds to collectors in range. The interval is
configurable (seconds or minutes).
T2
Bidirectional
868 MHz
Bidirectional version of T1.
R2
Bidirectional
868 MHz
The frequent receive mode prevents multiple metering
devices from interfering with each other by using
separate frequency channels.
N1
Unidirectional
169 MHz
This mode is optimized for narrowband and long range
N2
Bidirectional
169 MHz
Bidirectional version of N1. This mode doesn't support
N2g, which requires 4-GFSK modulation.
F2-m
Bidirectional
433 MHz
Bidirectional communication. It works on NRZ data
encoding.
Description
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3.1.1
Wireless M-Bus protocol overview
Mode
Communication
Frequency
band
Description
F2
Bidirectional
433 MHz
Bidirectional communication. It works on NRZ data
encoding.
C1
Unidirectional
868 MHz
Unidirectional communication. It works on NRZ data
encoding.
C2
Biidirectional
868 MHz
Bidirectional communication. It works on NRZ data
encoding.
Stationary mode (S Mode)
This is intended for unidirectional or bidirectional communications between the meter and a
stationary or mobile device.



3.1.2
S1 transmit only sub-mode has a long header and is optimized for stationary battery
operated devices
S1-m sub-mode is designed for mobile receivers
S2 mode is bidirectional
Frequent transmit mode (T Mode)
In this mode, the meter transmits a very short frame (typically 3 to 8 ms) every few
seconds, thus allowing walk-by and drive-by readouts.


3.1.3
T1 transmit only sub-mode is limited to the minimal, periodic transmission of meter ID
plus a readout value
T2 bidirectional sub-mode frequently transmits a short frame containing at least its ID
and then waits for a very short period after each transmission for a response, which
triggers bidirectional communication.
Alternatively, the initial frame also contains the readout value and the response is a
reverse channel reserved for special services.
Frequent receive mode (R2 Mode)
In this mode, the meter listens every few seconds for the reception of a wakeup message
from a mobile transceiver, whereupon the device prepares for a few seconds of dialog with
the initiating transceiver.
A multi-channel receive mode allows the simultaneous readout of several meters on
separate frequency channels.
3.1.4
Narrowband VHF mode (N-Mode)
This mode is optimized for narrowband operation in the 169-MHz frequency band allocated
for meter reading and other services.


N1a-f covers transmit only sub-modes
N2a-f covers bidirectional sub-modes.
The range of sub-modes can be extended using repeaters.
3.1.5
Frequent receive and transmit mode (F-Mode)
This mode is a frequent receive and transmit mode for long range communication in the
433 MHz band.
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Wireless M-Bus protocol overview


3.1.6
F2-m is the bidirectional sub-mode where the meter listens every few seconds for a
wake up signal from a stationary or mobile transceiver, upon which the device
prepares for a few seconds of dialog with the initiating transceiver.
F2 is the bidirectional sub-mode where the device transmits a frame and waits a short
period for a response, which triggers bidirectional communication.
Compact Mode (C-Mode)
This compact Mode operates in the 868 MHz Band. It is similar to the T-Mode, but sends
more info with the same energy. It functions in Unidirectional/Bidirectional mode. All
communication from the Meter to Other devices is in the form of FSK Modulated data and
all communication from Other Device to Meter takes place as GFSK Modulated data. All
communication is NRZ encoded.


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C1 Mode: Unidirectional Mode
C2 Mode: Bidirectional Mode
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4
Wireless M-Bus physical layer
Wireless M-Bus physical layer
The physical structure of the frame includes the preamble (header plus synchronization
fields), payload and postamble, as per the figure below.
Figure 5: Wireless M-Bus physical structure.
4.1
Frame structure
4.1.1
Preamble
The preamble consists of the header plus synchronous patterns.
The synchronization word required by EN-13757-4 is 18 bits for S and R modes, 10 bits for
T mode, 16 bits for N mode etc. The synchronization word is always preceded by the
preamble sequence.
4.1.2
Payload
The block structure of the payload field storing the data to be transmitted is configured in
the firmware.
4.1.3
Postamble (trailer)
The number of ‘01’ sequences is added to the postamble at the end of packet as per the
wM-Bus standard.
4.2
Physical layer files
The firmware files for the Wireless M-Bus physical layer are:


wmbus_phy.c routines
wmbus_phy.h headers
Figure 6: Physical layer directory structure
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Wireless M-Bus link layer
5
Wireless M-Bus link layer
The wM-Bus link layer is compliant with EN13757-4:2013 to interface the physical layer
(Phy) and the application layer (AL).
5.1
Data link layer functions
The data link layer





5.2
provides services to transfer data between the physical and application layers
generates outgoing CRC and verifies CRCs for incoming messages
provides wM-Bus addressing
acknowledges transfers for bidirectional communication modes
wM-Bus frame formation and verification of incoming frames
Link layer specification
The Wireless M-Bus standard supports two different, A and B, frame formats.
In both formats:


5.2.1
the first block has a fixed length of 10 bytes and includes the frame length (L-field), the
control information (C-field) and the sender address (link layer address).
the second block starts with the CI-field which declares the data structure.
Frame format A
Transmission frame format A complies with IEC 60870-5-1 format type FT3.
The first byte of the first block is the length field which specifies the number of subsequent
user data bytes, including the control and address bytes and excluding the CRC bytes. If
((L-9) MOD 16) is not zero, then the last block shall contain ((L-9) MOD 16) data bytes + 2
CRC bytes. All the other blocks except the first block shall always contain 16 data bytes + 2
CRC bytes.
Table 3: First block (format A)
L-field
C-field
M-field
A-field
CRC-field
1 byte
1 byte
2 bytes
6 bytes
2 bytes
Table 4: Second block (format A)
CI-field
Data-field
CRC-field
1 byte
15 or if it is the last block (((L-9) modulo 16) – 1) bytes
2 bytes
Table 5: Optional block (format A)
5.2.2
Data-field
CRC-field
16 or if it is the last block ((L-9) modulo 16) bytes
2 bytes
Frame format B
The first byte of the first block is the length field which specifies the number of all
subsequent bytes including all CRC bytes.
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Wireless M-Bus link layer
Table 6: First block (format B)
L-field
C-field
M-field
A-field
1 byte
1 byte
2 bytes
6 bytes
Table 7: Second block (format B)
CI-field
Data-field
CRC-field
1 byte
115 or if it is the last block (L-12) bytes
2 bytes
Table 8: Optional block (format B)
5.2.3
Data-field
CRC-field
(L-129) bytes
2 bytes
The L-field
The L-field is the first byte of the first block.


5.2.4
frame format A: consists of subsequent user data, control and address bytes,
excluding CRC.
frame format B: includes all subsequent bytes including CRC.
The C-Field
The general bit sequence structure of the C-field is shown below:
Figure 7: The C-Field
RES:

always '0’
PRM:


'1' message from primary (initiating) station
'0' message from secondary (responding) station
FCB, FCV and ACD, DFC:

5.2.5
all bit coded according to EN 60870-5-2.
Manufacturer ID (M-field)
The 15 least significant bits of these two bytes form a three letter ISO 646 code (A…Z), as
per clause 5.6 of EN 13757-3:2013. If the most significant bit is zero, then the address A
must be a unique (hard coded) 6-byte manufacturer meter address. Any type of coding or
numbering, including type/version/date may be used, as long as the ID is unique.
5.2.6
Address (A-field)
This address field A always contains the address of the sender (e.g., address of a meter
with integrated RF-Module or address of an RF-Adapter hosting a meter without RFInterface). It must at least be unique within the maximum transmission range, and it is the
responsibility of each user/manufacturer to guarantee this.
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Wireless M-Bus link layer
If this protocol is used together with the Transport Layer or the Application Layer of EN
13757-3, then the A-field address structure is a concatenation of the 'Identification number',
'Version number' and 'Device type information'.
5.2.7
CI-field
The CI-field is the application header and specifies the type of data in the application data
payload. While EN13757-4:2011 specifies a limited number of values, the Link Service
Primitives allow any value to be used.
5.2.8
Data field

5.2.9
The user data to be transmitted is stored in this field.
Cyclic redundancy check (CRC-field)
The CRC calculation is based on the information from the previous block according to FT3
of EN 60870-5-1.
The formula is:

The CRC polynomial is: x16 + x13 + x12 + x11 + x10 + x8 + x6 + x5 + x2 + 1
The initial value is 0; the final CRC is complemented.
5.3
Link layer firmware implementation
5.3.1
File description
The Link Layer Directory structure is shown below:
Figure 8: Link layer directory structure
The wM-Bus link layer implementation files are:





5.3.2
State machine flow structure

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wmbus_link.c routines
wmbus_link.h headers
wmbus_linkcommand.c command routines
wmbus_linkcommand.h headers for wmbus_linkcommand.c
wmbus_crc.c wM-Bus CRC routines
There are two separate state machines for meters and other devices, where different
events move the devices from IDLE to a new state according to the following state
machine transition tables.
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Wireless M-Bus link layer
Table 9: State machine table for meters
Current State
Event
Next State
SND-UD
LL_SM_SEND_ACK
SND-UD2
LL_SM_SEND_RSP_UD
REQ-UD2
LL_SM_SEND_RSP_UD
LL_SM_SEND_RSP_UD (If Alarm Data
available )
LL_SM_IDLE
REQ-UD1
LL_SM_SEND_ACK (If Alarm Data not
available )
CNF-IR
-
SND-NKE
-
ACK
LL_SM_SEND_ACC_NR
LL_SM_SEND_ACK
LL_SM_ACK_FAC_STATE
If(nRepeatation<= N)
LL_SM_SEND_ACK
If(nRepeatation > N)
LL_SM_IDLE
LL_SM_ACK_FAC_STATE
LL_SM_SEND_RSP_UD
LL_SM_RSPUD_FAC_STATE
LL_SM_SEND_ACC_NR
LL_SM_WAIT_STATE
If(nRepeatation<= N)
LL_SM_SEND_RSP_UD
If(nRepeatation> N)
LL_SM_IDLE
If(time <tResponseMax)
Wait to receive command
If(time >tResponseMax)
LL_SM_IDLE
SND-NR
-
ACC-NR
-
SND-IR
LL_SM_SEND_CNF_IR
ACC-DMD
LL_SM_SEND_ACK
RSP-UD
LL_SM_IDLE
LL_SM_RSPUD_FAC_STATE
LL_SM_WAIT_STATE
LL_SM_IDLE
If DataReqFlag is TRUE:
LL_SM_SEND_REQ_UD2
ACK
If ResetLinkFlag is TRUE:
LL_SM_SEND_NKE
If SendDataFlag is TRUE:
LL_SM_SEND_SND_UD
LL_SM_SEND_CNF_IR
LL_SM_IDLE
LL_SM_SEND_ACK
LL_SM_IDLE
LL_SM_SEND_REQ_UD2
LL_SM_WAIT_RSP_UD
If(time <=Timeout)
Wait to receive command
If(time>Timeout)
LL_SM_IDLE
LL_SM_WAIT_RSP_UD
LL_SM_SEND_NKE
LL_SM_IDLE
LL_SM_SEND_SND_UD
LL_SM_WAIT_ACK
If(time <=Timeout)
Wait to receive command
If(time>Timeout)
LL_SM_IDLE
LL_SM_WAIT_ACK
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Wireless M-Bus link layer
Table 10: State machine table for other devices
Current State
LL_SM_IDLE
Event
Next State
SND-NR
-
ACC-NR
-
SND-IR
LL_SM_SEND_CNF_IR
ACC-DMD
LL_SM_SEND_ACK
RSP-UD
LL_SM_IDLE
If DataReqFlag is TRUE:
LL_SM_SEND_REQ_UD2
ACK
If ResetLinkFlag is TRUE: LL_SM_SEND_NKE
If SendDataFlag is TRUE:
LL_SM_SEND_SND_UD
LL_SM_SEND_CNF_IR
LL_SM_IDLE
LL_SM_SEND_ACK
LL_SM_IDLE
LL_SM_SEND_REQ_UD2
LL_SM_WAIT_RSP_UD
LL_SM_WAIT_RSP_UD
Wait to receive command
If(time>Timeout)
LL_SM_IDLE
LL_SM_SEND_NKE
LL_SM_IDLE
LL_SM_SEND_SND_UD
LL_SM_WAIT_ACK
LL_SM_WAIT_ACK
5.4
If(time
<=Timeout)
If(time
<=Timeout)
Wait to receive command
If(time>Timeout)
LL_SM_IDLE
Application layer dependent parameters
Certain application layer dependent parameters for the link layer are passed from the
application layer to the link layer through “WMBusLinkAppliParams_t” according to the
following structure:
typedef struct
{
uint8_t LinkEllLength;/*!<Extended link layer length*/
uint8_t LinkHeaderLength;/*!<Header length*/
uint16_t LinkManufrID;/*!<Manufacturing id*/
uint32_t LinkDeviceID;/*!<Device identification number*/
uint8_t LinkDeviceVersion;/*!<Device version*/
uint8_t LinkMeterType;/*!<Meter type*/
uint8_t LinkAccessNumber;/*!<Access Number*/
uint8_t LinkStatusField;/*!<Status field*/
uint16_t LinkConfigWord;/*!<Configuration word*/
uint32_t LinkTimeout; /*!<User defined timeout*/
uint8_t LinkFreqAccessCycle;/*!<Frequent Access Cycle*/
ExtendedLinkLayer_t LinkEllType;/*!<Extended link layer type*/
uint8_t LinkEllAccessNum;/*!<Extended link layer access number*/
}WMBusLinkAppliParams_t;
“LinkAppliParams” is the “WMBusLinkAppliParams_t”-type structure defined in the link
layer and is initialized by the application layer in the “WMBus_LinkSetAppliParams”
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Wireless M-Bus link layer
function via pointer. The user then calls the “WMBus_LinkSetAppliParams” function from
the application layer to set the user-dependent parameters for the link layer.
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Revision history
6
Revision history
Table 11: Document revision history
20/21
Date
Version
Changes
02-Dec-2015
1
Initial release.
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IMPORTANT NOTICE – PLEASE READ CAREFULLY
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