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Create and Process Messages Using Database Definitions

This example shows you how to create, receive and process messages using information stored in CAN database files. This example uses the CAN database file, demoVNT_CANdbFiles.dbc.

Open the Database File

Open the database file and examine the Messages property to see the names of all message defined in this database.

db = canDatabase('demoVNT_CANdbFiles.dbc')
db.Messages
db = 

  Database with properties:

             Name: 'demoVNT_CANdbFiles'
             Path: '/tmp/Bdoc19a_1099451_29784/tpea833daf/ex80654288/demoVNT_CANdbFiles.dbc'
            Nodes: {}
         NodeInfo: [0x0 struct]
         Messages: {5x1 cell}
      MessageInfo: [5x1 struct]
       Attributes: {}
    AttributeInfo: [0x0 struct]
         UserData: []


ans =

  5x1 cell array

    {'DoorControlMsg'   }
    {'EngineMsg'        }
    {'SunroofControlMsg'}
    {'TransmissionMsg'  }
    {'WindowControlMsg' }

View Message Information

Use messageInfo to view message information, including the identifier, data length, and a signal list.

messageInfo(db, 'EngineMsg')
ans = 

  struct with fields:

             Name: 'EngineMsg'
     ProtocolMode: 'CAN'
          Comment: ''
               ID: 100
         Extended: 0
            J1939: []
           Length: 8
              DLC: 8
              BRS: 0
          Signals: {2x1 cell}
       SignalInfo: [2x1 struct]
          TxNodes: {0x1 cell}
       Attributes: {}
    AttributeInfo: [0x0 struct]

You can also query for information on all messages at once.

messageInfo(db)
ans = 

  5x1 struct array with fields:

    Name
    ProtocolMode
    Comment
    ID
    Extended
    J1939
    Length
    DLC
    BRS
    Signals
    SignalInfo
    TxNodes
    Attributes
    AttributeInfo

View Signal Information

Use signalInfo to view signal definition information, including type, byte ordering, size, and scaling values that translate raw signals to physical values.

signalInfo(db, 'EngineMsg', 'EngineRPM')
ans = 

  struct with fields:

             Name: 'EngineRPM'
          Comment: ''
         StartBit: 0
       SignalSize: 32
        ByteOrder: 'LittleEndian'
           Signed: 0
        ValueType: 'Integer'
            Class: 'uint32'
           Factor: 0.1000
           Offset: 250
          Minimum: 250
          Maximum: 9500
            Units: 'rpm'
       ValueTable: [0x1 struct]
      Multiplexor: 0
      Multiplexed: 0
    MultiplexMode: 0
          RxNodes: {0x1 cell}
       Attributes: {}
    AttributeInfo: [0x0 struct]

You can also query for information on all signals in the message at once.

signalInfo(db, 'EngineMsg')
ans = 

  2x1 struct array with fields:

    Name
    Comment
    StartBit
    SignalSize
    ByteOrder
    Signed
    ValueType
    Class
    Factor
    Offset
    Minimum
    Maximum
    Units
    ValueTable
    Multiplexor
    Multiplexed
    MultiplexMode
    RxNodes
    Attributes
    AttributeInfo

Create a Message Using Database Definitions

Specify the name of the message when you create a new message to have the database definition applied. CAN signals in this messages are represented in engineering units in addition to the raw data bytes.

msgEngineInfo = canMessage(db, 'EngineMsg')
msgEngineInfo = 

  Message with properties:

   Message Identification
    ProtocolMode: 'CAN'
              ID: 100
        Extended: 0
            Name: 'EngineMsg'

   Data Details
       Timestamp: 0
            Data: [0 0 0 0 0 0 0 0]
         Signals: [1x1 struct]
          Length: 8

   Protocol Flags
           Error: 0
          Remote: 0

   Other Information
        Database: [1x1 can.Database]
        UserData: []

View Signal Information

Use the Signals property to see signal values for this message. You can directly write to and read from these signals to pack or unpack data from the message.

msgEngineInfo.Signals
ans = 

  struct with fields:

    VehicleSpeed: 0
       EngineRPM: 250

Change Signal Information

Write directly to the signal to change a value and read its current value back.

msgEngineInfo.Signals.EngineRPM = 5500.25
msgEngineInfo.Signals
msgEngineInfo = 

  Message with properties:

   Message Identification
    ProtocolMode: 'CAN'
              ID: 100
        Extended: 0
            Name: 'EngineMsg'

   Data Details
       Timestamp: 0
            Data: [23 205 0 0 0 0 0 0]
         Signals: [1x1 struct]
          Length: 8

   Protocol Flags
           Error: 0
          Remote: 0

   Other Information
        Database: [1x1 can.Database]
        UserData: []


ans = 

  struct with fields:

    VehicleSpeed: 0
       EngineRPM: 5.5003e+03

When you write directly to the signal, the value is translated, scaled, and packed into the message data using the database definition.

msgEngineInfo.Signals.VehicleSpeed = 70.81
msgEngineInfo.Signals
msgEngineInfo = 

  Message with properties:

   Message Identification
    ProtocolMode: 'CAN'
              ID: 100
        Extended: 0
            Name: 'EngineMsg'

   Data Details
       Timestamp: 0
            Data: [23 205 0 0 71 0 0 0]
         Signals: [1x1 struct]
          Length: 8

   Protocol Flags
           Error: 0
          Remote: 0

   Other Information
        Database: [1x1 can.Database]
        UserData: []


ans = 

  struct with fields:

    VehicleSpeed: 71
       EngineRPM: 5.5003e+03

Receive Messages with Database Information

Attach a database to a CAN channel that receives messages to apply database definitions to incoming messages automatically. The database decodes only messages that are defined. All other messages are received in their raw form.

rxCh = canChannel('MathWorks', 'Virtual 1', 2);
rxCh.Database = db
rxCh = 

  Channel with properties:

   Device Information
            DeviceVendor: 'MathWorks'
                  Device: 'Virtual 1'
      DeviceChannelIndex: 2
      DeviceSerialNumber: 0
            ProtocolMode: 'CAN'

   Status Information
                 Running: 0
       MessagesAvailable: 0
        MessagesReceived: 0
     MessagesTransmitted: 0
    InitializationAccess: 1
        InitialTimestamp: [0x0 datetime]
           FilterHistory: 'Standard ID Filter: Allow All | Extended ID Filter: Allow All'

   Channel Information
               BusStatus: 'N/A'
              SilentMode: 0
         TransceiverName: 'N/A'
        TransceiverState: 'N/A'
       ReceiveErrorCount: 0
      TransmitErrorCount: 0
                BusSpeed: 500000
                     SJW: []
                   TSEG1: []
                   TSEG2: []
            NumOfSamples: []

   Other Information
                Database: [1x1 can.Database]
                UserData: []

Receive Messages

Start the channel, generate some message traffic and receive messages with physical message decoding.

start(rxCh);
generateMsgsDb();
rxMsg = receive(rxCh, Inf, 'OutputFormat', 'timetable');
rxMsg(1:15, :)
ans =

  15x8 timetable

        Time         ID     Extended           Name               Data        Length      Signals       Error    Remote
    _____________    ___    ________    ___________________    ___________    ______    ____________    _____    ______

    0.0055522 sec    100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.0055565 sec    200     false      'TransmissionMsg'      [1x8 uint8]      8       [1x1 struct]    false    false 
    0.0055595 sec    400     false      'DoorControlMsg'       [1x8 uint8]      8       [1x1 struct]    false    false 
    0.0055622 sec    600     false      'WindowControlMsg'     [1x4 uint8]      4       [1x1 struct]    false    false 
    0.0055632 sec    800     false      'SunroofControlMsg'    [1x2 uint8]      2       [1x1 struct]    false    false 
    0.017925 sec     100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.042928 sec     100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.042939 sec     200     false      'TransmissionMsg'      [1x8 uint8]      8       [1x1 struct]    false    false 
    0.067925 sec     100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.092921 sec     100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.092927 sec     200     false      'TransmissionMsg'      [1x8 uint8]      8       [1x1 struct]    false    false 
    0.11793 sec      100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.11793 sec      400     false      'DoorControlMsg'       [1x8 uint8]      8       [1x1 struct]    false    false 
    0.14295 sec      100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.14296 sec      200     false      'TransmissionMsg'      [1x8 uint8]      8       [1x1 struct]    false    false 

Stop the channel and clear it from the workspace.

stop(rxCh);
clear rxCh

Examine a Received Message

Inspect a received message to see the applied database decoding.

rxMsg(10, :)
rxMsg.Signals{10}
ans =

  1x8 timetable

        Time        ID     Extended       Name           Data        Length      Signals       Error    Remote
    ____________    ___    ________    ___________    ___________    ______    ____________    _____    ______

    0.092921 sec    100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 


ans = 

  struct with fields:

    VehicleSpeed: 50
       EngineRPM: 3.5696e+03

Extract All Instances of a Specified Message

Use MATLAB notation to extract all instances of a specified message by name.

allMsgEngine = rxMsg(strcmpi('EngineMsg', rxMsg.Name), :);
allMsgEngine(1:15, :)
ans =

  15x8 timetable

        Time         ID     Extended       Name           Data        Length      Signals       Error    Remote
    _____________    ___    ________    ___________    ___________    ______    ____________    _____    ______

    0.0055522 sec    100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.017925 sec     100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.042928 sec     100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.067925 sec     100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.092921 sec     100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.11793 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.14295 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.16793 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.19287 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.21793 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.24293 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.26795 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.29293 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.31793 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.34293 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 

Plot Physical Signal Values

Plot the values of database decoded signals over time. Reference the message timestamps and the signal values in variables.

signalTimetable = canSignalTimetable(rxMsg, 'EngineMsg');
signalTimetable(1:15, :)
plot(signalTimetable.Time, signalTimetable.VehicleSpeed)
title('Vehicle Speed from EngineMsg', 'FontWeight', 'bold')
xlabel('Timestamp')
ylabel('Vehicle Speed')
ans =

  15x2 timetable

        Time         VehicleSpeed    EngineRPM
    _____________    ____________    _________

    0.0055522 sec          0             250  
    0.017925 sec           0             250  
    0.042928 sec          50          3569.6  
    0.067925 sec          50          3569.6  
    0.092921 sec          50          3569.6  
    0.11793 sec           50          3569.6  
    0.14295 sec           50          3569.6  
    0.16793 sec           55          3621.3  
    0.19287 sec           55          3621.3  
    0.21793 sec           55          3621.3  
    0.24293 sec           55          3621.3  
    0.26795 sec           55          3621.3  
    0.29293 sec           55          3663.9  
    0.31793 sec           55          3663.9  
    0.34293 sec           55          3663.9