MATLAB Examples

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.

Contents

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: 'C:\TEMP\Bdoc18a_805738_11608\ib4C766E\15\tp75927dcd\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
    _____________    ___    ________    ___________________    ___________    ______    ____________    _____    ______

    0.0027752 sec    100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.0027803 sec    200     false      'TransmissionMsg'      [1x8 uint8]      8       [1x1 struct]    false    false 
    0.0027883 sec    400     false      'DoorControlMsg'       [1x8 uint8]      8       [1x1 struct]    false    false 
    0.0027925 sec    600     false      'WindowControlMsg'     [1x4 uint8]      4       [1x1 struct]    false    false 
    0.0027948 sec    800     false      'SunroofControlMsg'    [1x2 uint8]      2       [1x1 struct]    false    false 
    0.028624 sec     100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.053625 sec     100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.053631 sec     200     false      'TransmissionMsg'      [1x8 uint8]      8       [1x1 struct]    false    false 
    0.077588 sec     100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.10259 sec      100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.1026 sec       200     false      'TransmissionMsg'      [1x8 uint8]      8       [1x1 struct]    false    false 
    0.12794 sec      100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.12794 sec      400     false      'DoorControlMsg'       [1x8 uint8]      8       [1x1 struct]    false    false 
    0.15359 sec      100     false      'EngineMsg'            [1x8 uint8]      8       [1x1 struct]    false    false 
    0.1536 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
    ___________    ___    ________    ___________    ___________    ______    ____________    _____    ______

    0.10259 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
    _____________    ___    ________    ___________    ___________    ______    ____________    _____    ______

    0.0027752 sec    100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.028624 sec     100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.053625 sec     100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.077588 sec     100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.10259 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.12794 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.15359 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.17854 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.20356 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.22864 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.25348 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.27856 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.30358 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.32856 sec      100     false      'EngineMsg'    [1x8 uint8]      8       [1x1 struct]    false    false 
    0.35283 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
    _____________    ____________    _________

    0.0027752 sec          0             250  
    0.028624 sec          50          3569.6  
    0.053625 sec          50          3569.6  
    0.077588 sec          50          3569.6  
    0.10259 sec           50          3569.6  
    0.12794 sec           50          3569.6  
    0.15359 sec           55          3621.3  
    0.17854 sec           55          3621.3  
    0.20356 sec           55          3621.3  
    0.22864 sec           55          3621.3  
    0.25348 sec           55          3663.9  
    0.27856 sec           55          3663.9  
    0.30358 sec           55          3663.9  
    0.32856 sec           55          3663.9  
    0.35283 sec           55          3663.9