Application Note AN067 - TI

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Application Note AN067Wireless MBUS Implementation with CC1101 and MSP430By Patrick SeemKeywords 1 Wireless MBUSKNX-RFMeter readingData rate offset and driftFrequency offset and driftMSP430Synchronization wordPacket length modesCRCData coding and encodingCC1101IntroductionThis application note describes how theCC1101 and MSP430 combined can beconfigured to a modem that complies withthe Wireless MBUS standard [1]. ThewirelessMBUSstandardisacommunication standard for meters andwireless readout of meters, and specifiesthe physical and the data link layer. Powerconsumption is a critical parameter for themeter side, since the communication linkSWRA234shall be operative for the full lifetime ofthe meter, without changing the battery.CC1101 combined with MSP430 is anexcellent choice for the Wireless MBUSstandard. CC1101 is a truly low cost, lowpower and flexible transceiver, andMSP430 a high performance and ultra lowpower MCU. The source code discussedin this application note can be ge 1 of 37

Application Note AN067Table of ContentsKEYWORDS. 11 INTRODUCTION . 12 ABBREVIATIONS. 33 WIRELESS MBUS . 43.1 KNX-RF . 44 PHYSICAL LAYER . 54.1 RADIO LINK A REQUIREMENTS . 54.2 RADIO LINK B REQUIREMENTS . 65 DATA LINK LAYER . 85.1 DATA CODING . 85.2 PREAMBLE AND SYNCHRONIZATION WORD . 85.3 PACKET FORMAT . 85.4 CRC - FIELD. 96 RADIO IMPLEMENTATION . 106.1 CRYSTAL TOLERANCE .106.2 RECEIVER FILTER BANDWIDTH .106.2.1 Radio Link A . 116.2.2 Radio Link B . 116.3 FREQUENCY OFFSET AND DRIFT COMPENSATION. 116.4 DATA RATE OFFSET AND DRIFT COMPENSATION . 116.5 FREQUENCY DEVIATION OFFSET .126.6 CARRIER SENSE .127 DATA LINK LAYER IMPLEMENTATION . 137.1 DATA ENCODING .137.2 PREAMBLE, SYNCHRONIZATION WORD IN TRANSMIT MODE . 137.2.1 Radio Link A . 137.2.2 Radio Link B . 137.3 SYNCHRONIZATION WORD IN RECEIVE MODE . 137.3.1 Radio Link A . 147.3.2 Radio Link B . 147.4 PACKET LENGTH CONTROL .147.5 CRC . 148 RADIO PERFORMANCE . 158.1 RADIO LINK A . 158.1.1 Receiver Sensitivity . 158.1.2 Summary . 188.2 RADIO LINK B . 198.2.1 Receiver Sensitivity . 198.2.2 Summary . 219APPLICATION SOFTWARE DOCUMENTATION . 239.1 APPLICATION USER GUIDE .239.2 TRANSMIT MODE.239.2.1 MCU Load . 249.3 RECEIVE MODE . 259.3.1 MCU Load . 279.4 IMPROVEMENTS.2710 REFERENCES . 2811 DOCUMENT HISTORY. 28APPENDIX A . 29APPENDIX B . 32APPENDIX C . 36APPENDIX D . 37SWRA234Page 2 of 37

Application Note KNRZIFPERBERKNXLCDSoCLPMEvaluation moduleIndustrial, Scientific, MedicalMetering BusCyclic Redundancy CheckTransmitReceiveMost Significant BitLeast Significant BitFirst In First OutMicro Controller UnitFrequency Shift KeyingNon Return to ZeroIntermediate FrequencyPacket Error RateBit Error RateKonnexLiquid Crystal DisplaySystem on Chip, used in this document to reference CC111xLow Power ModeSWRA234Page 3 of 37

Application Note AN0673Wireless MBUSThe wireless MBUS standard specifies the communication between a meter and an “other”system component, e.g. mobile/stationary readout devices, data collectors. See Figure 1 for asimple overview of a wireless MBUS nFigure 1. Wireless MBUS Communication SystemThree different meter modes with sub-modes are defined, for the communication between ameter and an “other”. S-mode, Stationary Modeo S1-mode, one-way communication from meter to “other”o S1m-mode, one-way communication from meter to “other”o S2-mode, two-way communication between meter and “other” T-mode, Frequent Transmit Modeo T1-mode, one-way communication from meter to “other”o T2-mode, two-way communication between meter and “other” R-mode, Frequent Receive Modeo R2-mode, two-way communication between meter and “other”R2-mode is out of the scope for this application note.3.1KNX-RFThe physical layer and the data link layer of KNX-RF were defined jointly with the wirelessMBUS standard, and S-mode complies with the KNX-RF standard.SWRA234Page 4 of 37

Application Note AN0674Physical LayerAll of the presented radio requirements are taken from the wireless MBUS specification [1].Only two different radio links are defined, which will be named radio link A and B in thisapplication note. Table 1 shows the mapping between the different wireless MBUS modesand the two radio links.ModeLinkS-mode Meter - OtherRadio Link AS-mode Other - MeterRadio Link AT-mode Meter - OtherRadio Link BT-mode Other - MeterRadio Link ATable 1. RF Link MappingSince the Wireless MBUS standard operates in the 868-870 ISM band, the radiorequirements must also comply with the ETSI EN 300 220 [2] and CEPT/ERC/REC 70-03 E[3] standards. An introduction to these requirements, and how CC1101 complies with theserequirements, can be found in application note AN050 [4].Requirements that are applicable for the application layer are not considered in thisapplication note, e.g. Duty cycle Response delayThe implementation should still ensure that the transceiver is configured to terminate TX andRX automatically when a packet is transmitted or received.Three different performance classes of transceivers are defined in the wireless MBUSstandard, and the radio requirements presented comply with the highest performance class.4.1Radio Link A RequirementsThe requirements are summarized in Table 2, Table 3 and Table 4.Common Radio ParameterMinTypicalMaxUnitCommentFrequency Table 2. RF Requirements RF Link ASWRA234Page 5 of 37

Application Note AN067Transmit Radio ParameterMinTypicalMaxUnitCommentCarrier Frequency (other)868.278868.3MHz 25 ppmCarrier Frequency (meter)868.25868.3868.322868.35MHz 60 ppmFrequency deviation 40 50 80kHzBaud rate32.768Baud rate driftkbaud 1.5%Table 3. TX Requirements RF Link AReceive Radio ParameterMinTypicalSensitivity (BER 10-2)-100-105dBm32.768kbaudBaud rateBaud rate driftMaxUnitComment 2%Table 4. RX Requirements RF Link A4.2Radio Link B RequirementsThe requirements are summarized in Table 5, Table 6 and Table 7.Common Radio ParameterMinTypicalMaxUnitCommentFrequency n2-FSKTable 5. RF Requirements RF Link BTransmit Radio ParameterMinTypicalMaxUnitCommentCarrier Frequency868.90868.95869.00MHz 60 ppmFrequency deviation 40 50 80kHzBaud rate90100110kbaudBaud rate drift 1%Table 6. TX Requirements RF Link BSWRA234Page 6 of 37

Application Note AN067Receive Radio ParameterMinTypicalSensitivity (BER 10-2 )-100-105Baud rate88100Baud rate driftMaxUnitCommentdBm112kbaud 2%Table 7. RX Requirements RF Link BSWRA234Page 7 of 37

Application Note AN0675Data Link layerAll of the presented data link requirements are taken from the wireless MBUS specification[1]. For detailed explanation of the different fields in a packet and the data coding, see thewireless MBUS specification.5.1Data CodingData coding used for the different radio links are shown in Table 8.Data codingData / baud rateLinkManchester1/2Radio Link A3 out of 6 coding2/3Radio Link BTable 8. Wireless MBUS Data Coding5.2Preamble and Synchronization WordPreamble and synchronization word for the different radio links are shown in Table 9.Preamblen*(01)nSync wordnLink00 0111 0110 1001 0110Postamblen*(01)279 n2 n 415 n00 0111 0110 1001 0110n*(01)2 n 419 n00 0011 1101n*(01)2 n 4Radio Link A,long preambleRadio Link A,short preambleRadio Link Bn*(01)n*(01)Table 9. Pre/postamble and Synchronization WordThe long preamble sequence for radio link A is used for the S1-mode, and optionally for theS2-mode.Note that the preamble, synchronization word and postamble sequences are not data coded.5.3Packet FormatA packet will consist of A preamble sequence and a synchronization word Block 1 and block 2 as shown in Table 10 and Table 11 respectively Optionally n blocks, determined by the packet length, as shown in Table 12 Postamble sequenceL-Field1 byteC-field1 byteM-field2 bytesA-field6 bytesCRC–field2 bytesTable 10. Block 1 FormatSWRA234Page 8 of 37

Application Note AN067CI-field1 byteData field15 bytes or ( ((L-9) mod 16) -1) bytesCRC field2 bytesTable 11. Block 2 FormatData field16 bytes or ( (L-9) mod 16) bytesCRC field2 bytesTable 12. Optional block(s) formatThe length field excludes the following fields CRC fields L-Field5.4CRC - fieldThe CRC polynomial is x16 x13 x12 x11 x10 x8 x6 x5 x2 1, with 0 as initial value. Thefinal CRC is complementedSWRA234Page 9 of 37

Application Note AN0676Radio ImplementationBoth Radio Link A and Radio Link B radio register configurations are based on the followingpreferred setting from SmartRF studio: 325 kHz RX filter bandwidth GFSK with 47 kHz frequency deviation 100 kbaud data rate Sensitivity optimizedThe radio register configuration for the 2 radio links can be found in appendix C and D.6.1Crystal ToleranceFrequency drift in the transceiver is due to the crystal inaccuracy. E.g. A crystal inaccuracy of 40 ppm, will give a frequency drift of 40 ppm. A more detailed description on frequencydrift and crystal tolerance can be found in design note DN005 [6]. For the implementation tocomply with the strictest TX radio link requirement, the maximum crystal tolerance is 25ppm.6.2Receiver Filter BandwidthThe bandwidth of the RX filter is an important parameter. If the bandwidth is set too small thewanted RX signal is filtered out. If the bandwidth is set too large it will degrade the sensitivity.Carlson’s rule is used to estimate the bandwidth of the FSK modulated signal, where f isthe frequency deviation and fmod is frequency of the modulation signal.BWFSK 2 ( f fmod )For an NRZ signal, 2 fmod equals the baud rate.Following parameters must be taken into account when determining the bandwidth of thereceived RX signal. Frequency drift in the receiver and transmitter Baud rate drift Frequency deviation driftThe RX filter bandwidth, BWRX, should be selected so that the RX signal occupies at most80% of the signal RX filter bandwidth. If frequency offset compensation is disabled, the RXfilter bandwidth can be calculated by the following equation.BWRX (BWFSK , MAX 2 fdrift , MAX )0,8When frequency offset compensation is enabled, the IF is continuously adjusted so that theRX signal is aligned with the RX filter. This implies that the frequency offset/drift can beignored from the RX filter bandwidth calculation, but note that the frequency error is estimatedafter the RX filter. Hence the modulation index to the RX signal is one of the main parametersthat will determine how much frequency offset/drift can be ignored.h ffmodFor a FSK signal with a large modulation index the RF spectrum will have two distinct peaks,e.g. the signal effect is not centered. This implies that the frequency offset/drift cannot betotally ignored from RX filter bandwidth calculation. On the other hand, for a FSK signal with aSWRA234Page 10 of 37

Application Note AN067small modulation index the frequency offset/drift can be ignored from the RX filter bandwidthcalculation.6.2.1 Radio Link AMaximum bandwidth of the FSK signal isBWFSK 2 80kHz 33kHz 193kHzThis will give the following RX filter bandwidth when ignoring frequency offset/drift from thecalculation.BWRX 1930,8 242kHzSince the modulation index is large for an RX signal with maximum frequency deviation,frequency offset/drift should not be totally ignored from the calculation. Hence a BWRX of 270kHz is selected for radio link A.6.2.2 Radio Link BMaximum bandwidth of the FSK signal isBWFSK 2 80kHz 112kHz 272kHzThis will give the following RX filter bandwidth when ignoring frequency offset/drift from thecalculation.BWRX 2720,8 340HzSince the modulation index is low, even for an RX signal with maximum frequency deviation,frequency offset/drift can be ignored from the calculation. Hence a BWRX of 325 kHz isselected for radio link B.6.3Frequency Offset and Drift CompensationFrequency offset compensation is controlled from the FOCCFG register, and notcompensating for frequency drift will degrade the receiver sensitivity. The RX bandwidthselection also requires that frequency offset compensation is enabled.Maximum frequency offset for both links, given the requirements, is 25 ppm 60 ppm 85 ppmfdrift fcarrier 85 ppm 74kHzHence the saturation limit for the frequency offset compensation loop (FOC LIMIT) should beset to BWRX / 4.The pre gain factor determines the frequency offset tracking. The post gain factor determinesthe frequency drift tracking. The post gain factor can be reduced, since the frequency drift isoften limited.6.4Data Rate Offset and Drift CompensationData rate offset compensation is controlled from the BSCFG register. Failing to compensatefor data rate offset will give a packet error rate of 100 % in synchronous mode when the datarate offset is large. This is because the bit synchronization is lost, independently of thestrength of the received signal.SWRA234Page 11 of 37

Application Note AN067For radio link A, the maximum data rate drift in the system is 2 %, and hence the saturationlimit for the data rate offset compensation loop (BC LIMIT) must be set to 3.125 %.For radio link B, the maximum data rate drift in the system is 12 %, and hence thesaturation limit for the data rate offset compensation loop (BC LIMIT) must be set to 12.5 %.Setting the FOC BS CS GATE bit ensures that noise does not make the data rate driftalgorithm drift away to the limit before the carrier is sensed. Given the short preamblesequence of only 4-5 bytes and the large data rate offset, it is important that theFOC BS CS GATE bit is set.When given a short preamble the data rate compensation loop is not perfectly symmetrical,and it can be problems with locking at data rate offsets above 7 %. Hence several packetscan be lost even with strong signal inputs, since the synchronization word is not detected. Toget minimum degradation in performance in the 12 % range, the data rate setting for thereceiver should be set to 102-103 kbaud. Note also that the wireless MBUS standard limitsthe transmitter data rate offset to 10 %.The pre gain factors, pre Ki and pre Kp, determine the data rate offset tracking. The post gainfactors, post Ki and post Kp, determine the data rate drift tracking.The pre gain factors for the algorithms should be increased from the default valu

KNX-RF Meter reading Data rate offset and drift Frequency offset and drift MSP430 Synchronization word Packet length modes CRC Data coding and encoding CC1101 . 1 Introduction . This application note describes how the CC1101 and MSP430 combined can be configured to a modem that complies with the Wireless .

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