Periodic CAN Communication in MATLAB

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This example shows you how to how to configure CAN channels and messages for transmit messages periodically. It uses MathWorks® virtual CAN channels connected in a loopback configuration.

As this example is based on sending and receiving CAN messages on a virtual network, running CAN Explorer in conjunction may provide a more complete understanding of what the code is doing. To run CAN Explorer, open and configure it to use the same interface as the receiving channel of the example. Make sure to start CAN Explorer before beginning to run the example in order to see all of the messages as they occur.

This example describes the workflow for a CAN network, but the concept demonstrated also applies to a CAN FD network.

Create the CAN Channels

Create CAN channels for message transmission and reception.

txCh = canChannel("MathWorks", "Virtual 1", 1);
rxCh = canChannel("MathWorks", "Virtual 1", 2);

Open the DBC file that contains message and signal definitions, and attach it to both CAN channels.

db = canDatabase("CANDatabasePeriodic.dbc");
txCh.Database = db;
rxCh.Database = db;

Create the CAN Messages

Create CAN messages EngineMsg and TransmissionMsg using the database information.

msgFast = canMessage(db, "EngineMsg")

msgFast = 
  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: []

msgSlow = canMessage(db, "TransmissionMsg")

msgSlow = 
  Message with properties:

   Message Identification
    ProtocolMode: 'CAN'
              ID: 200
        Extended: 0
            Name: 'TransmissionMsg'

   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: []

Configure Messages for Periodic Transmission

To enable a message for periodic transmission, use the transmitPeriodic command specifying the transmitting channel, the message to register on the channel, a state value, and the periodic rate.

transmitPeriodic(txCh, msgFast, "On", 0.100);
transmitPeriodic(txCh, msgSlow, "On", 0.500);

Start the Periodic Transmission

Start the receiving channel.

start(rxCh);

Start the transmitting channel with periodic transmission configured in the previous step. Period transmission begins immediately. Allow the channels to run for two seconds.

start(txCh);
pause(2);

Update Transmitted Data

To update the live messages or signal data transmitted onto the CAN bus, write new values directly to the VehicleSpeed signal in message EngineMsg.

msgFast.Signals.VehicleSpeed = 60;
pause(1);
msgFast.Signals.VehicleSpeed = 65;
pause(1);
msgFast.Signals.VehicleSpeed = 70;
pause(1);

Alternatively, you can write new values to the Data property of the created messages.

Receive the Messages

Stop the CAN channels and receive all periodically transmitted messages for analysis.

stop(txCh);
stop(rxCh);
msgRx = receive(rxCh, Inf, "OutputFormat", "timetable");

View the first few rows of the received messages using the head function.

head(msgRx)

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

    0.031922 sec    100     false      {'EngineMsg'      }    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.031924 sec    200     false      {'TransmissionMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.13752 sec     100     false      {'EngineMsg'      }    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.24011 sec     100     false      {'EngineMsg'      }    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.35028 sec     100     false      {'EngineMsg'      }    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.45648 sec     100     false      {'EngineMsg'      }    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.53209 sec     200     false      {'TransmissionMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.56215 sec     100     false      {'EngineMsg'      }    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false

Analyze the Behavior of Periodic Transmission

Analyze the distribution of messages by plotting the identifiers of each received message against their timestamps. Note the difference between how often the two messages appear according to the configured periodic rates.

plot(msgRx.Time, msgRx.ID, "x")
ylim([0 400])
title("Message Distribution", "FontWeight", "bold")
xlabel("Timestamp")
ylabel("CAN Identifier")

For further analysis, separate the two messages into individual timetables.

msgRxFast = msgRx(strcmpi("EngineMsg", msgRx.Name), :);
head(msgRxFast)

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

    0.031922 sec    100     false      {'EngineMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.13752 sec     100     false      {'EngineMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.24011 sec     100     false      {'EngineMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.35028 sec     100     false      {'EngineMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.45648 sec     100     false      {'EngineMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.56215 sec     100     false      {'EngineMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.66495 sec     100     false      {'EngineMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.77479 sec     100     false      {'EngineMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false

msgRxSlow = msgRx(strcmpi("TransmissionMsg", msgRx.Name), :);
head(msgRxSlow)

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

    0.031924 sec    200     false      {'TransmissionMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    0.53209 sec     200     false      {'TransmissionMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    1.0317 sec      200     false      {'TransmissionMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    1.5323 sec      200     false      {'TransmissionMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    2.0437 sec      200     false      {'TransmissionMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    2.5418 sec      200     false      {'TransmissionMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    3.0423 sec      200     false      {'TransmissionMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false 
    3.5422 sec      200     false      {'TransmissionMsg'}    {[0 0 0 0 0 0 0 0]}      8       {1×1 struct}    false    false

Analyze the timestamps of each set of messages to see how closely the average of the differences corresponds to the configured periodic rates.

avgPeriodFast = mean(diff(msgRxFast.Time))

avgPeriodFast = duration
   0.10604 sec

avgPeriodSlow = mean(diff(msgRxSlow.Time))

avgPeriodSlow = duration
   0.50141 sec

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

signalTimetable = canSignalTimetable(msgRx, "EngineMsg");
head(signalTimetable)

        Time        VehicleSpeed    EngineRPM
    ____________    ____________    _________

    0.031922 sec         0             250   
    0.13752 sec          0             250   
    0.24011 sec          0             250   
    0.35028 sec          0             250   
    0.45648 sec          0             250   
    0.56215 sec          0             250   
    0.66495 sec          0             250   
    0.77479 sec          0             250

Plot the received values of signal VehicleSpeed over time and note how it reflects the three updates in message data.

plot(signalTimetable.Time, signalTimetable.VehicleSpeed)
title("Vehicle Speed from EngineMsg", "FontWeight", "bold")
xlabel("Timestamp")
ylabel("Vehicle Speed")
ylim([-5 75])

View Messages Configured for Periodic Transmission

To see messages configured on the transmitting channel for automatic transmission, use the transmitConfiguration command.

transmitConfiguration(txCh)

Periodic Messages

ID  Extended      Name             Data        Rate (seconds)
--- -------- --------------- ----------------- --------------
100 false    EngineMsg       0 0 0 0 70 0 0 0  0.100000
200 false    TransmissionMsg 0 0 0 0 0 0 0 0   0.500000


Event Messages

None

Close the Channels and DBC File

Close access to the channels and the DBC file by clearing their variables from the workspace.

clear rxCh txCh
clear db