Manchester-NRZ Decoder, Documentation for Beta Testers
Contents
1. cccccssseccccseccceesececeeseceeeeeeceeeeeceesenseeeeas 13 Figure 20 Table view with too many 2s and 3s in Data ssssesessessensesrerssrrrsssreresrrrsssreresererssreresererssrereserersseere 13 Figure 21 Decoding a Burst into 2 Words Decode Tab in Word Mode no Nx field in this image pre 7 9 14 Figure 22 Comparison of Bit and Word Decode on the same signal ccccccssscccceeseccceeseceeeeeceeeeesceeeeneeeeeas 15 Figure 23 Payload bits grouped as repeated lt 1 1x8 2 gt DIOCKS ec ceccccceeeceseeeeeeseeecesseeeeceseeeeeseeeneeeeeas 16 Figure 24 Payload bits grouped as single lt 16 12x8 13 gt blocks eeccccceeseseecceeeesecceeeeeeseceeeeeeeeeceeeeaeeneeess 16 Figure 25 Payload bits grouped as repeated lt 4 2x8 5 gt DIOCKS cc ceeccccceeeccceeeeeeseeeeeseceuceseseeneceseeeeeeeeeneeeeeas 16 Figure 26 The Level Tab with default settings cceccccsssecccceseccecesececeesececceueceeseeseceseuaecessenecesseneceesenneeetes 17 Figure 27 Effect of the Level and Hysteresis values on the CECOING cccceseccccesecceeesececeeeceeeeseeeeeeseeeeas 17 Figure 28 Heavily zoomed image of the Level and Hysteresis rendering ccccccsseeccceesececeeseceeeeeeceeeeeseeeees 18 Figure 29 Correct decode of a clean Signal Level 50 Hysteresis 15 cccccecccccsssececeesececeeeeceeseeeeeeeeeseeeeas 19 Figure 30 Wrong decode of the same signal heavily perturbed Level 50 and2. It is also possible to use the Level in one Mode i e Absolute whereas Hysteresis is in the other Mode i e Percent In general the Percent Mode is more convenient and faster to setup because it immediately determines the optimal threshold However on poor signals the Percent Mode can fail and lead to bad decodes Then it might help to use the Absolute Mode On very long signals the Percent Mode adds computational load If performance is an issue it might be beneficial to switch to Absolute mode Before we continue let s emphasize the visual rendering of Level and Hysteresis again Hysteresis is fairly subtle as it should not dominate the rendering of the decoded information Lahniss Manchester NRZ BUS Documentation Page 17 Figure 28 Heavily zoomed image of the Level and Hysteresis rendering In this Figure the level appears as a blue dotted line highlighted with a blue circle while the Hysteresis is annotated as a dark grey band yellow line The next section will discuss an example of a bad signal decoded by tuning the Level and hysteresis settings Lahniss Manchester NRZ BUS Documentation Page 18 How to tune Level and hysteresis when working on noisy signals We will now look at an example of a noisy signal that will not decode correctly with the default Level and Hysteresis values The first image shows the reference decoding of a clean Manchester signal with 16 transitions 11 bits of values 000 1101 0100 Auirst
3. 1 16 Trans tor 44 Bits T d o Figure 29 Correct decode of a clean Signal Level 50 Hysteresis 15 When noise is added to the signal various wrong decoding symptoms appear such as 2 s and 3 s non contiguous bits too many transitions here 37 and fake bits on the idle portion The reason is that the signal spikes create fake transitions where it crosses the Level Threshold with insufficient hysteresis Red markers Note that if we were decoding in Word Mode other errors would appear but with the same root cause Urete 2S Trans tor 44 Bits Ae Figure 30 Wrong decode of the same signal heavily perturbed Level 50 and Hysteresis 15 As soon as we increase the hysteresis the spikes no longer cross the hysteresis band and the decoding converges back to correct values In this image note the expanded Hystersis annotation band around the bue dotted level marker line Burst 1 16 Trane Figure 31 Correct decoding on Noisy Signal with Level at 50 but Hysteresis at 3 Divisions Finally another method using a numerical Filter Median Filter to smoothen the noise and still decode with default Level and Hysteresis 1 TL ei fa ZHE ad FA jin Figure 32 Correct decoding on Filtered Signal with Default level and Hysteresis Lahniss Manchester NRZ BUS Documentation Page 19 A philosophical comment and a word of caution Although the above numerical tricks have shown that it is possible to decode a noisy
4. Bi Phase Space always Midbit change 0 no change at bit start and 1 changes Lahniss Manchester NRZ BUS Documentation Page 10 We have now covered all the controls in the Basic tab When all of these values are set we should already have a basic bit level decoding on the trace selected as a source Note that by default the Data Mode is set to bits so that the setting of the second tab do not matter for the initial bit level decode The following picture shows a correct decoding the bit transitions are all aligned with the signal transitions the logical interpretation of the bits are consistent with the physical level in this case Physical High equals logical 1 Note that the decoding at an exact multiple of the bitrate could seem correct but would not allow further interpretation of the words This image shows the decoding of the same signal portion at twice the bitrate The next section will refine the interpretation and take the decoding one level of abstraction higher the word level Lahniss Manchester NRZ BUS Documentation Page 11 5 The Decode Tab The bit level decode reached in the previous section can be taken further so that some transitions are skipped and subsequent bits are grouped into words and the words interpreted Isb first or msb first We will not explain the classical encoding schemes here but refer to selected Internet contributions i e as in http ckp made it com encodingschemes
5. Hysteresis 15 cees 19 Figure 31 Correct decoding on Noisy Signal with Level at 50 but Hysteresis at 3 DiVISIONS 0000000 19 Figure 32 Correct decoding on Filtered Signal with Default level and Hysteresis cccccesseceeeeseeeeeeeseeeees 19 Lahniss Manchester NRZ BUS Documentation Page 2 1 Introduction The Manchester NRZ Decoder developed by Lahniss for LeCroy oscilloscopes is a tool aimed at decoding serial data that is not supported by main stream decoders and whose structure is reasonably simple to be described with the 10 20 controls explained below It was born out of recurring customers request for decoding fairly simple serial data not belonging to the historical protocols such as 12C UART and SPI or the dedicated protocols such as CAN LIN MIL 1553 ARINC 429 MIPI Ethernet etc The diagram below exemplifies the situation simple Protocols Complex The complexity ladder of protocols Protocols UART I2C EFABUS ARINC CAN FlexRay SPI 8b10b 2S 1553 MIPI Ethernet Figure 1 Complexity ladder of protocols In that spirit the user is required to configure a number of controls making it possible for the general algorithms to execute on his particular signal This process requires a little more knowledge of serial data encoding logic than previous decoders but the explanations below should shed some light on the procedure Once the setting have been determined for a given signal they can be s
6. PrePad Bits The PrePad Bits are used to group information preceding the Data Bits There might be O to 32 PrePad Bits PrePad bits might be used to group Address bits Preambles Subaddress etc The Nx Factor This value allows the replication of several Data Words defined by the Data bits Its default is 1 meaning that there is only one Data word with the defined number of Data bits When the value is set to one the grouping of bits into words occurs as a repeated sequence of lt Prepad Data PostPad gt blocks When the value is greater than 1 for example 3 the grouping of bits will occur as a repeated sequence of lt Prepad Data Data Data PostPad gt blocks Examples are shown below Lahniss Manchester NRZ BUS Documentation Page 14 Data Bits The number of bits grouped together to form a single word The Bits per Words can take values from 1 to 32 in steps of 1 This value is essential when using ProtoBusMAG because it allows the correct extraction of the bit field for MessageToValue parameter Post Pad Bits The PostPad Bits are used to group information following the Data Bits There might be O to 32 PostPad Bits Post Pad bit might be used to visually represent a CRC a checksum a Value or any other protocol construct There is however no CRC check Comparison of a Signal Decoded as Bits or Words The following annotated screen dump provides a time aligned comparison of the same signal decoded as bits
7. or corrupted signal these techniques do not replace the fundamental healthy signal hygiene Having good signal is the best way to avoid system failures or performance degradation The decoding techniques are meant to help until the signal is fixed There are many reasons for having poor signals bad lines poor components at every level in the circuitry EMC issues and many more and last but not least wrong probing techniques or even faulty oscilloscope The discussion of those is outside the realm of this manual but should be taken seriously Technical information A burst might contain at most 100000 transitions or 32000 bits or 1000 words whichever occurs first This is merely a safety limit for software engineering reasons then a limit based on any protocol The Bit rate limit is not an algorithmic limitation but rather is based on the availability of test signals for the extreme cases As for other decoders the limit might be expanded if and when signals at those speed are available to validate the algorithm Lahniss Manchester NRZ BUS Documentation Page 20
8. to both the NRZ and the Manchester Decoders Lahniss Manchester NRZ BUS Documentation Page 13 The tools offered by the Decoders allow a grouping of bits into PrePad Data Bits and PostPad The next image shows an example with the corresponding annotations 2 S31 Trans tor 34 Oits and 2 Words Word 1 PrePad Ox0e Dii Obie PostPad O0x0b PrePad 0x06 Siis Deiat PostPad 0x0 Word 2 Close Viewing Bit Order Words EX MSE First Trans Useq Bit Stretch Tol FrePad Liata Bite PostPad A 4 a A Figure 21 Decoding a Burst into 2 Words Decode Tab in Word Mode no Nx field in this image pre 7 9 The Viewing Hex This control Z 2lwill be used to choose how we want to view the PrePad Data Bits and PostPad both in the table and the annotations on the trace This parameter has no impact when Data Mode is Bits and is therefore grayed out Bit Order When decoding in Words this control selects a conversion of the Word with the Most Significant Bit first or the Least Significant Bit first This parameter has no impact when Data Mode is Bits and is therefore grayed out Sync Bits The Sync Bits lets the user choose at which bit the packetizing should start The algorithm will start at Sync Bits and group bits into the 3 fields PrePad Data Bits and PostPad Then it will restart with the PrePad of the next sequence There might be 0 to 100 Sync Bits
9. to decode jittery signals Conversely it can be decreased until the decoding starts showing anomalies to assess the stability of the midbit distribution Lahniss Manchester NRZ BUS Documentation Page 12 Interpretation of the Manchester bits tuning of Bit Slicer When decoding a serial stream as a Manchester it is normally expected to see Ones and Zeroes as explained above It is however possible that 2 s and 3 s appear in the decoded stream These values correspond to violations for the Manchester rules stating there must be a transition at midbit 3 53 Trans for 34 Bits Synchronization Pulse 2 00 ps Burst 3 53 Trans for 31 Bits Synchronization Pulse 2 00 ps Figure 19 Examples of Interaction between FTO and decoding These violations can be voluntary as in the MVB Multiple Vehicle Bus example above They often correspond to synchronization patterns used by the hardware to start the decoding In other cases the Highs and Lows carry information and allow the detection of different Frame types There is a nearly endless set of combinations used in various protocols The initial part of the Manchester packet is called different names in different protocols Preamble Start Of Frame Packet Header Packet Start etc In order to obtain a correct decoded stream the user needs to set the FTO in a way that the bits are correctly synchronized throughout the packet Usually this can be achieved by setting the Bitrate first as in
10. Manchester NRZ Decoder Documentation for Beta Testers August 2012 January 2013 Oct 2015 IDIC OT CONTENTS Manchester NRZ Decoder Documentation for Beta Testers c cccccccscssscscsceesesscesseesseusseusseusseesseusseusseusseusseuscs 1 1 ATOU ON a A AE 3 2 FUndi APIS Ta VE I CANIN E a E E ania ueasenwenaaiast 4 3 Cee 02 10 r en Oe er ere eee ee eee 5 4 The Basic Tab Bit Level DECOING ccecccccssseccceesececcescceeeesececseneceeseusecessusecesseneceeseesecessunecesseneceeseneeeetas 7 BC RNS sa ateacecnpasesopnatupes E E E A E A E 7 el ERS E E ae E A E ee A A E A A A A E ee E 7 BE VU RV erien E OS 7 TES CS crore asters ot verte E E E E A EA E E 8 TAC UE E a A E EE E EE E E E T E E 8 TC OUE E O E ee ee E E E eee 8 UE MM OE e E S A E E a EAE 8 Polarity Manchester Standard and NRZ renisicsnsrnoii a a E G a 9 The different Manchester Encoding Types cccccsssecccccessecccceeesecceseeeseccessueeeeeesaeseecessaeneeeeesaeaseeeesuaaeeessuaneeeessaansses 10 Verifying the Bit Level DCC OG es cicscatesresraucindcioanicne cadciawsbacaeaesantdaleandelen andecudsisanisameatdanacaweniceasantiueaaaaegnunbosaniauasdencsatacetcsashcousaats 11 RS CO A sass hac seen seats pic ce nash gs ee E anne aeaes teases cnoasacaponacecueaaasee seuneesse 12 TG MN OC aici savant siete ese psn te ede enor aera tenes soe esint seeders econ snes ene ea gece sedan oes aadee ehdnnwecas basausticnrcadsenbeunaseenroes 12 Decadine m OBI aaar cease co
11. Stretch Tol 0 10 0 Grouping of Bits into Words Sync Bits PrePad Nx ici PostPad 2 1 1 8 2 Figure 23 Payload bits grouped as repeated lt 1 1x8 2 gt blocks This structure is frequently found in UART type protocols when consecutive characters are being transmitted over the line Each character is made up of a start bit s data bits and stop bit s Burst 48 94 Trans 127 Bits 12 Words __ PrePad 0x6666 Data 0xc9 Data 0x35 Data 0x55 Data 0x6a Data 0x59 Data 0x56 Data 0x55 Data 0x56 Data 0x96 Data 0x65 Data 0x59 Data 0x56 PostPad 0x1993 innit N i i i i i r Basic Decode Levels Data Mode Viewing Bit Order Words Hex MSB First Trans Used Bit Stretch Tol 0 10 0 Grouping of Bits into Words Sync Bits PrePad Data Bits PostPad 2 16 12 8 13 Figure 24 Payload bits grouped as single lt 16 12x8 13 gt blocks Another frequently found structure with an initial ID or Destination several adjacent Data bytes and a trailing field Burst 48 94 Trans 127 Bits 10 Words Data Oxaa Oxad Data Ox4b Data 0x56 Data 0x66 Data eee Oxi2 0x06 Data Oxaa Data EcL Data 0x55 Data 0x95 Hai Ox0b Data 0x4b Data 0x32 0x15 oxog Pata 0x56 Data Oxcc wi l Basic Decode Levels Data Mode Viewing Bit Order Words Hex MSB First Trans Used Bit Stretch Tol 0 10 0 Grouping of Bits into Words Sync Bit
12. ab ccccccccsssssecccceesecceceeeseccecseeeecesseeeeeessuaueeeesseaneeeessuaneees 17 How to tune Level and hysteresis when working ON noisy signals ccccsssssecccccessecccceesseccecaeeeeceecaeaeeceeseeaeecesseaaeeeeees 19 A philosophical comment and a word of CAUTION ccccccccssssscecceeesecceceeeeceeccaeeeeeesaeseecesseaueeeessaeaseeeesseanseeessaaneeeessaaasses 20 TOCCATO NAOT oree a sacs acndeacanesbeansuauccacenecasaesaosieceonessannsoonscecseasaansseaudeeessnstecaseanecedsens ssacneneeeaase 20 Lahniss Manchester NRZ BUS Documentation Page 1 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Complexity ladder Of ProtOcols ccscccccsssccccessececeesececceneccceesecessusececeeueceeseusccesausecessenececseaeeeeseeaeeeten 3 PMS Cy Pe DA T cits ees tac casas E econo a teic uicwnian baa potaceaternce Wisaines suaiemsion aaaoananaeense nae 5 The Signal Source and Protocol Selection Didlog cccccccsssecccesseccccensececeesececseeeceeeeesecessuseceteugeceeseges 5 The 3 tabs Basic Decode Levels driving Manchester and NRZ decode ccccccceeeeseceeeeseseeeeeseenes 6 TAEDE rc ana ee ee eee eC eee ee ree ee eee eons 7 Example of a Timeout Definition Use Timeout assumed cccccccceesseccccceeesecccceeeeeeceeseeeeceeeseenaeeess 8 Manchester Physical to Logical mapping Case Falling O ccc
13. as a logical One The NRZ Polarity When Low 0 is chosen a low level signal state below threshold will translate as a logical zero whereas a governs the conversion of the physical signal transition into a logical bit state high level above threshold signal will translate as a logical 1 The opposite logic will apply when Low 1 is selected The image below shows a Manchester example Polarity Falling 0 Figure 7 Manchester Physical to Logical mapping case Falling 0 When Falling 1 the opposite logic will be applied leading to the following image of the low level decode annotation Falling 1 Figure 8 Manchester Physical to Logical mapping case Falling 1 Lahniss Manchester NRZ BUS Documentation Page 9 The different Manchester Encoding Types There exists a great variety of Manchester encoding The current implementation supports the 4 versions documented on this page A stream of about 40 bits is shown in every case and allows the association of the physical signal with the logical signal according to the encoding at hand Manchester Standard Falling O Figure 9 Manchester Standard Falling 0 Rising 1 Manchester Standard Falling 1 Figure 10 Manchester Standard Falling 1 Rising 0 Differential Bi Phase Mark Figure 11 Differential Bi Phase Mark always Midbit change 1 no change at bit start and 0 changes Differential Bi Phase Space Figure 12 Differential
14. ccccessccccessececeeseceeeeeseeeeeeseceseueeceesenes 9 Manchester Physical to Logical mapping case Falling 1 cece cessccccessececeesecceeeeeeeessesecetseneceesenes 9 iVianchester Standard Falling 0 RISING ccssichsccecsencecactuneapswerdessnsidesiaciespacaxbesauiainwnteunedediscedeaiocewcuade 10 Manchester Standard Falling 1 RiSinG O cccccccsssccecessececeesececeescceceesececseneceeeeeeceesseseeessugesss 10 Differential Bi Phase Mark always Midbit change 1 no change at bit start and 0 changes 10 Differential Bi Phase Space always Midbit change 0 no change at bit start and 1 changes 10 Figure 13 Correct NRZ decoding at 1 1IMID Sisiccccssssesvsssnncnnsiedsatsnetieostanaessiedsadenntnntanadnieetvesionaecsiesisasuuntennndsanoensen 11 Figure 14 Incorrect NRZ Bit level decoding of same signal at 2 MD S ccccccccccccceeeseseesseeeseeeeeeeeeseseeeeeeeeauaeens 11 Figure 15 Incorrect NRZ Bit level Decode the bits are not aligned with the transitions c ccescceeseeeeeees 11 Figure 16 Incorrect NRZ Bit Level Decode gaps between the bits 0 eeccccesseccccesseeeeeeseceeeeeeceeseeeceeeeneeeeees 11 Feure 17 Decode Tapin BE NOOC ensena E A Ganucsaanensincsniaeeenaneodenteaeeenceetores 12 Figure 18 The Table Mode selection popup sssessssssssesssreesrrrsssrerssrrerssreresrrrsssrereserrnsseeresererssreresererssreresereessrere 12 Figure 19 Examples of Interaction between FTO and decoding
15. dentification of the Burst controls then extract the Bits and finally the Words by grouping the Words The words Burst Frames or Packets are used in interchangeable manner in this document and in general literature Later we will address the decoding of many Packets into the same record therefore allowing the observation of the encoded data values over a period of time The decoder settings determined on a few packets will be reused when handling many packets In order to start the decoding we need to be familiarized with the User Interface of the Decoder Firstly in the Serial Decode dialog you need to select the signal source here C1 and the Protocol Manchester in this case Decode Setup S view Decode Decode 1 Di LIF iF ee Manchester s Decode 2 Table Rows Source 1 Data Frotocol 5 ii Action for decoder E a A a Export Output File a hle clLeCrovia DecodeTable csv Browse Decode 4 TT Configure Measure Search Table Once the Manchester or NRZ Protocol has been selected 3 tabs will appear in the Right Hand Side Dialog We will be setting various values in these 3 tabs Basic Decode Level When working on a given signal some of the values in the tabs will not change anymore because they are strongly linked to the signal i e Bit Rate or Polarity Other values will have to be tuned to obtain optimal results Some of the controls can be used to reverse
16. engineer unknown signals Lahniss Manchester NRZ BUS Documentation Page 5 Bitrate Idle State Polarity 5 00000 Mbit s Dont Care Low 0 Use Encoding Timeout Standard Figure 4 The 3 tabs Basic Decode Levels driving Manchester and NRZ decode The Use Timeout selection allows decoding of continuous streams when unchecked Lahniss Manchester NRZ BUS Documentation Page 6 4 The Basic Tab Bit Level Decoding The Basic tab presents all the fundamental controls necessary to allow proper bit level decoding We will look at each control individually Bitrate idle State Polarity 73 00 kbit s Dont Care ee E Encoding Units standard Figure 5 The Basic Tab Bit Rate Bitrate 9 60 kbitts Introduce the Bit Rate of your signal here as precisely as you know it Hardware engineers working on a design often know the Bit Rate If you are not sure about the value use the cursor read outs on one single bit or a sequence of bits to determine the exact Bit Rate of your signal The value should be correct within about 5 Note that a mismatched Bit Rate will cause various confusing side effects on the decoding so it is best to take time to correctly adjust this fundamental value Bit Rates can be selected from 10 bits s to 10 Gb s Idle State g i Lo yy IdleHigh Dont Care The idle State has to be started the algorithm looks at the time elapsed between 2 consecutive Transitions as well as the com
17. eout in Seconds As an alternative to the Timeout in Bits the value can be expressed directly in seconds This is useful in protocols with a timeout spec expressed in time units The following image provides an example of the controls and their effect on the annotation ees Basic Bitrate Idle State P rit 1 50000 Mbits IdleLow Falling 0 Units Seconds Figure 6 Example of a Timeout Definition Use Timeout assumed In the Figure above a Timeout of 2 micro seconds has been selected The grey rectangle on the trace shows this timeout as well as the value selected by the user Note that the value of 2 us is adequate to separate the 2 Bursts of transmission Furthermore this protocol requires the timeout span to be Idle low which is set in the Idle State control Idle low refers to the Threshold level marked as a dotted line Use Timeout When this control is unchecked the stream will no longer be packetized This is sometimes useful on high speed protocols which have continuous bit streaming Lahniss Manchester NRZ BUS Documentation Page 8 Polarity Manchester Standard and NRZ Falling 0 Falling 1 The Manchester Polarity governs the conversion of the physical signal transition into a logical bit state In Manchester When Falling 0 is chosen a falling edge through the threshold level will be decoded as a logical Zero whereas a rising edge through the threshold level will be decoded
18. html http www rhyshaden com encoding htm The following image shows the decode tab when Data Mode is Bits In this Mode most of the controls are grayed out indicating that they have no action As soon as we select Data Mode as Words the grayed out fields will become active Basic Decode Levels Close Data Mode Bits Hex First Trans Used Bit Stretch Tal i 10 0 Figure 17 Decode Tab in Bit Mode The Data Mode This control drives the level of decoding desired Initially make sure you select Bits Bits is also the default value when starting the decoder words Figure 18 The Table Mode selection popup Decoding into Bits We have already looked at the low level decoding in bits in the previous section There are a few more items to look at as part of the Bit Level decoding Then we will address the Word level decoding First Transition Used FTO Many Manchester or NRZ encoding schemes utilize a preamble a synchronization sequence or a voluntary Manchester violation The FTO can be used to start the decoding after the violation where the real data payload starts It avoids the intricacies of dedicated protocols in the initial segment of each packet Bit Stretch Tolerance The Manchester bit slicer hops from midbit to midbit However due to hardware or signal propagation issues the midbits might not be perfectly equidistant In this case the tolerance can be manually increased to attempt
19. or words Here again the action of every control can be verified and explained Burst 48 94 Trans 127 Bits 100110011001 000 a 0 a 00 0 0 0 00 a a 0 0 000 00 0 0001000 00 T000 00 0 00 00 0000 r l M yii Wilh Mil ki a n Burst 45 94 Trans 127 Bits 13 Words n 0x09 Ox05 0x02 Oxia ann Ox Mie OxOa Ox0b Ox m 0x09 are iF LEE nE na mne na nemna D oTo kosi TENS FUK CU U0 0x03 Dabo ead Une Uno UPC UOC UCU Uo ULES UL Jo Ux fat CAUT USU r e w01 0x04 0x Close Viewing Bit Orde Words Hex MSB First Trans Used Bit Stretch Tol 10 0 Sync Bits PrePad Nx Data Bits PosiPad 3 4 3 Figure 22 Comparison of Bit and Word Decode on the same signal This case shows an NRZ signal physical high and logical 1 The 127 bits of both signals are time aligned to allow an easy understanding of how the Prepad Data and PostPad fields get constructed Note that here the Nx factor is set to 1 to only allow one Data field The subsequent section will show other combinations Lahniss Manchester NRZ BUS Documentation Page 15 Comparison of Signal Decoded with varying Nx This section shows the same signal decoded using 3 common variations Burst 48 94 Trans 127 Bits 12 Words Data Ox6c Data 0x9a 02 Data 0x55 02 Data Ox4b 00 Data 0x56 01 Data Oxaa Data EAN CEI Data Oxca Data 0x95 03 02 02 02 01 Data Oxcc Decode Levels Data Mode Viewing Bit Order Words Hex MSB First Trans Used Bit
20. plements the Timeout value set previously In order to declare that a new Burst state of the idle level between these transitions This mechanism allows a precise definition of what the separation gap between 2 Bursts should be In most cases the idle state is specified and therefore provides an additional condition to the timeout to define the Burst start If this distinction is not desired select Don t care in the popup box Encoding Standard Diff Biphase Mark Diff Biphase Space The encoding control Manchester only allows the selection of several Manchester flavors When Standard is selected the Polarity control is visible when any other encoding is chosen the Polarity disappears The differences will be explained below with exemples Lahniss Manchester NRZ BUS Documentation Page 7 Timeout Units Seconds Both methods are The Timeout or Gap separating Burst can be selected either in Bits or Seconds perfectly equivalent in terms of their results but depending on the context the protocol specifications or the user preference one or the other representations might be chosen Note that regardless of the Timeout Units selected the allowed Timeout range will be from 1 bit to 100 bits Timeout in Bits When a Timeout in bits is selected as in our example above the system will use the Bit Rate to determine the Bit Length and multiply it by the number of bits selected to obtain a Timeout in seconds Tim
21. s PrePad Nx DataBis PosiPad 2 4 2 8 5 Figure 25 Payload bits grouped as repeated lt 4 2x8 5 gt blocks This structure is less frequent but possible and combines above examples into blocks The use of the above controls allows a flexible and rich decomposition of the payload databits Lahniss Manchester NRZ BUS Documentation Page 16 6 The Level Tab The contents and actions of the controls in the Level Tab The last tab to be discussed is the level tab The image below shows its contents Ss ae Basic Levels More lose Level and Hysteresis have to be carefully chosen to cross pul es of all amplitudes Level Type Level Percent 50 0 Hysteresis Type Hysteresis Percent im 15 Figure 26 The Level Tab with default settings The next image will show the effect of the controls when using the percent mode Levels hiore Close TT Burst 1 16 Trans for 11 Bits Level and Hysteresis have to be carefully chosen to cross pulses of all amplitudes Level Type Percent HY steresis Ty He Fercent Figure 27 Effect of the Level and Hysteresis values on the decoding When working in percent all the values are proportional to the 100 signal amplitude In the example the level of 68 refers to the 100 amplitude shown The same applies to the Hysteresis Both Level and Hysteresis can be switched to Type Absolute In this case the values need to be set in Volts Both methods have their merits
22. s terete vases eva ca esci eee aye cie preset EE E E aa anette ancays A ees oeeunenequsanceaaneee 12 First Transition Used FTO cccesssccccccccessecccceceueseeeccceeeuessececeeeeuenseececeseuanseeeceessueaseeeeceseauanseeeceeeeuassseeeeseseueseeeeeseaugeseeeeeesegggeeess 12 PreTre EE E E EE EE sao sede E 12 Interpretation of the Manchester bits tuning of Bit Slicer sossennssseenessrensssreressreressreressreressreressreressreressreressreressseressseresseeeeee 13 SC OCIS ION AS aesa T E E E O E E EE AE A OE ns 13 Converting Burst BITS into VW OFS siccristssszrtdecssceistaasdcbavatiertstaandes nstseeiatoundeaanmauerishoengedimstueedstounteianoniarisbouadaiinstsnalstcunbeiaxstanstuuageintice 13 WS UN EAA ec sce gic AAA AE N A A eases A EA cance A S EE N E EEA S A Guest AA 14 P OTE e E E N NEE E E E E E E E E A E E E 14 N BI ea E TE TE E TE E E E 14 Propad E are E E E EE EE EE AEA EEE E OA ER EEEE EEA EEE EAEE TEREN 14 ENEE CO ea a E E E E sense cence 14 ANS D ea A E E E A E A E E A E 15 PO EPB a E E EEE E EE A E E E E A EE E E AE 15 Comparison of a Signal Decoded as Bits or WordsS ccccccccssseecccceeseccccaesecccccauueecceseaseeceeseeeecesssauseeeesuanseeessaaneeeessages 15 Comparison of Signal Decoded with varying NX cccccsssseccccessseccccsesecceseaeeceesaeseeceesseueeeeeseeeecesseeasecesseaaseeessaaaeeeessages 16 AE E a a E E E E A ET E S E A E E E E E T 17 The contents and actions of the controls in the Level T
23. ssion line e Then each Burst needs to be sliced into Bits using the Transitions the Bitrate and Polarity and the Type either NRZ or Manchester e Finally the Bursts of Bits can be converted to Words using the Bits previously extracted and based on grouping rules The Bit conversion will not be functional before the Bursts are correctly separated with their Transitions and the Words extraction will not function correctly until the Bits are properly decoded The process is a 3 level stepwise method The tuning of the Decoder must therefore be conducted in this order Transitions gt Bits gt Words The following material will guide the operator through every step of the process beginning at the Transitions level and ending at the Words level Lahniss Manchester NRZ BUS Documentation Page 4 3 Getting started In order to get started with the Manchester NRZ Decoder it is advisable to adjust the scope controls to acquire one Burst or Frame of relevant Data and then stop the acquisition The data Burst should be reasonably well centered on screen in both directions with generous idle segments on both sides A LeCroy WREOAZI Lc e je File Wertic al Timehase Trigger Display Cursors We assure biath Analysis Utilitie s Burst of Data Once the Burst of Data to be decoded is acquired we will proceed to its interpretation using either the Manchester or the NRZ Decoder We will proceed gradually starting with the i
24. the previous section Then The Transition Tolerance might have to be enlarged from its default of 20 see above When the signal is stable it might be decreased to less than 5 without changing the output of the Decoder observed in the table In the example below the many 2s and 3s in the Data indicate an incorrect phasing of the bit decoder with the signal More tuning is required before the Word Level can be used Data NonData IFG Status 12311100001111110010 29 2us Burst 1 53 Trans for 31 Bits 11312310232132130000 3 5 us Burst 2 51 Trans for 33 Bits ee PUTT a ae et es 47 us Burst 3 53 Trans for 31 Bits 11312310232132130000 3 5 Us Burst 4 51 Trans for 33 Bits T US Burst 5 50 Trans for 31 Bits VI AVATOT VOT VO 104141 4 Figure 20 Table view with too many 2s and 3s in Data Note that the Word decoder will silently process bits with values of 2 and 3 but the results will be incorrect Decoding into Words We have now achieved a correct bit level decoding and we can look at higher level concepts Converting Burst Bits into Words This is achieved by selecting the Data Mode Words When this mode is selected all of the fields become accessible Unlike decoding into bits the conglomeration of bits into words does no longer depend upon the physical layer In other words the bits can be grouped to form words regardless of their origin NRZ Manchester or else As a consequence the mechanisms described below apply
25. tored in normal panel files and recalled later when analysis on the same signal are required In its current form the configurable Decoder operates on NRZ or Manchester streams e The product wil handle digitally encoded data on a single signal with 2 levels High and Low a constant Bitrate between 10 bit sec to 60 Gb sec at any voltage levels and a timeout or Inter Frame Gap allowing to separate bursts of data on the line e The product will not handle multi line signals signals with more than 2 voltage levels stuff bits and or complex synchronization pulses This product whilst flexible is not suitable for complex protocol streams such as i e CAN CAN FD MIL STD 1553 FlexRay MIPI or 2 or 3 signal transmissions such as 12C or SPI For these protocols the dedicated decoders are available So this software component is more of a toolbox aimed at supporting many different streams that have some basic characteristics in common and a limited market that does not justify a dedicated decoder Lahniss Manchester NRZ BUS Documentation Page 3 2 Fundamental mental model Before we get started we need to emphasize the methodology underlying the software described here The fundamental model is a 3 step model The signal needs to be decoded as e Burst s first with their constitutive Transitions based on the Bitrate and the Timeout Definition Bursts are separated by Holes or electrically soeaking quiescent times on the transmi
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