Use DBC Files in CAN Communication

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This example shows you how to create, receive and process messages using information stored in DBC files. This example describes the workflow for a CAN network, but the concept demonstrated also applies to a CAN FD network.

Open the DBC File

Open file demoVNT_CANdbFiles.dbc using canDatabase.

db = canDatabase("demoVNT_CANdbFiles.dbc")

db = 
  Database with properties:

             Name: 'demoVNT_CANdbFiles'
             Path: 'C:\Users\michellw\OneDrive - MathWorks\Documents\MATLAB\Examples\vnt-ex80654288\demoVNT_CANdbFiles.dbc'
            Nodes: {}
         NodeInfo: [0×0 struct]
         Messages: {5×1 cell}
      MessageInfo: [5×1 struct]
       Attributes: {}
    AttributeInfo: [0×0 struct]
         UserData: []

Examine the Messages property to see the names of all messages defined in this file.

db.Messages

ans = 5×1 cell
    {'DoorControlMsg'   }
    {'EngineMsg'        }
    {'SunroofControlMsg'}
    {'TransmissionMsg'  }
    {'WindowControlMsg' }

View Message Information

Use messageInfo to view information for message EngineMsg, 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: {2×1 cell}
       SignalInfo: [2×1 struct]
          TxNodes: {0×1 cell}
       Attributes: {}
    AttributeInfo: [0×0 struct]

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

messageInfo(db)

ans=5×1 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 information for signal EngineRPM in message EngineMsg, 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: [0×1 struct]
      Multiplexor: 0
      Multiplexed: 0
    MultiplexMode: 0
          RxNodes: {0×1 cell}
       Attributes: {}
    AttributeInfo: [0×0 struct]

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

signalInfo(db, "EngineMsg")

ans=2×1 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

Create a new message by specifying the database and the message name EngineMsg to have the database definition applied. CAN signals in this message 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: [1×1 struct]
          Length: 8

   Protocol Flags
           Error: 0
          Remote: 0

   Other Information
        Database: [1×1 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 and unpack data from the message.

msgEngineInfo.Signals

ans = struct with fields:
    VehicleSpeed: 0
       EngineRPM: 250

Change Signal Information

Write directly to the signal EngineRPM to change its value.

msgEngineInfo.Signals.EngineRPM = 5500.25

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: [1×1 struct]
          Length: 8

   Protocol Flags
           Error: 0
          Remote: 0

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

Read the current signal values back and note that EngineRPM has been updated with the written value.

msgEngineInfo.Signals

ans = struct with fields:
    VehicleSpeed: 0
       EngineRPM: 5.5003e+03

When a value is written directly to the signal, it is translated, scaled, and packed into the message data using the database definition. Note the value change in the Data property after a new value is written to the VehicleSpeed signal.

msgEngineInfo.Signals.VehicleSpeed = 70.81

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: [1×1 struct]
          Length: 8

   Protocol Flags
           Error: 0
          Remote: 0

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

msgEngineInfo.Signals

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: [0×0 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: [1×1 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");

View the first few rows of received messages.

head(rxMsg)

ans=8×8 timetable
       Time        ID     Extended            Name                       Data              Length      Signals       Error    Remote
    ___________    ___    ________    _____________________    ________________________    ______    ____________    _____    ______

    0.13103 sec    100     false      {'EngineMsg'        }    {[     0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.13103 sec    200     false      {'TransmissionMsg'  }    {[     0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.13104 sec    400     false      {'DoorControlMsg'   }    {[     0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.13104 sec    600     false      {'WindowControlMsg' }    {[             0 0 0 0]}      4       {1×1 struct}    false    false 
    0.13105 sec    800     false      {'SunroofControlMsg'}    {[                 0 0]}      2       {1×1 struct}    false    false 
    0.15598 sec    100     false      {'EngineMsg'        }    {[     0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.18 sec       100     false      {'EngineMsg'        }    {[172 129 0 0 50 0 0 0]}      8       {1×1 struct}    false    false 
    0.18001 sec    200     false      {'TransmissionMsg'  }    {[     4 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false

Stop the receiving 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, :)

ans=1×8 timetable
       Time        ID     Extended        Name                   Data              Length      Signals       Error    Remote
    ___________    ___    ________    _____________    ________________________    ______    ____________    _____    ______

    0.22994 sec    100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1×1 struct}    false    false

rxMsg.Signals{10}

ans = struct with fields:
    VehicleSpeed: 50
       EngineRPM: 3.5696e+03

Extract All Instances of a Specified Message

Extract all instances of message EngineMsg.

allMsgEngine = rxMsg(strcmpi("EngineMsg", rxMsg.Name), :);

View the first few instances of this specific message.

head(allMsgEngine)

ans=8×8 timetable
       Time        ID     Extended        Name                   Data              Length      Signals       Error    Remote
    ___________    ___    ________    _____________    ________________________    ______    ____________    _____    ______

    0.13103 sec    100     false      {'EngineMsg'}    {[     0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.15598 sec    100     false      {'EngineMsg'}    {[     0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.18 sec       100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1×1 struct}    false    false 
    0.20597 sec    100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1×1 struct}    false    false 
    0.22994 sec    100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1×1 struct}    false    false 
    0.25695 sec    100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1×1 struct}    false    false 
    0.27995 sec    100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1×1 struct}    false    false 
    0.30597 sec    100     false      {'EngineMsg'}    {[172 129 0 0 50 0 0 0]}      8       {1×1 struct}    false    false

Plot Physical Signal Values

Use canSignalTimetable to repackage signal data from message EngineMsg into a signal timetable.

signalTimetable = canSignalTimetable(rxMsg, "EngineMsg");

View the first few rows of the signal timetable.

head(signalTimetable)

ans=8×2 timetable
       Time        VehicleSpeed    EngineRPM
    ___________    ____________    _________

    0.13103 sec          0             250  
    0.15598 sec          0             250  
    0.18 sec            50          3569.6  
    0.20597 sec         50          3569.6  
    0.22994 sec         50          3569.6  
    0.25695 sec         50          3569.6  
    0.27995 sec         50          3569.6  
    0.30597 sec         50          3569.6

Plot the values of signal VehicleSpeed over time.

plot(signalTimetable.Time, signalTimetable.VehicleSpeed)
title("Vehicle Speed from EngineMsg", "FontWeight", "bold")
xlabel("Timestamp")
ylabel("Vehicle Speed")

Close the DBC File

Close access to the DBC file by clearing its variable from the workspace.

clear db

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