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CAN Unpack

Unpack individual signals from CAN messages

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  • CAN Unpack block

Libraries:
Vehicle Network Toolbox / CAN Communication
C2000 Microcontroller Blockset / Target Communication
Embedded Coder / Embedded Targets / Host Communication
Simulink Real-Time / CAN / CAN MSG blocks

Description

The CAN Unpack block unpacks a CAN message into signal data using the specified output parameters at every time step. Data is output as individual signals.

To use this block, you also need a license for Simulink® software.

The CAN Unpack block supports:

  • The use of Simulink accelerator and rapid accelerator modes. Using this feature, you can speed up the execution of Simulink models. For more information, see Acceleration (Simulink).

  • The use of model referencing. Using this feature, your model can include other Simulink models as modular components. For more information, see Model References (Simulink).

Tip

  • To process every message coming through a channel, it is recommended that you use the CAN Unpack block in a function trigger subsystem. See Using Triggered Subsystems (Simulink).

  • This block can be used to decode the signals of J1939 parameter groups up to 8 bytes. However, to work with J1939 messages, it is preferable to use the blocks in the J1939 Communication block library instead of this block. See J1939 Communication.

Examples

Periodic CAN Message Transmission Behavior in Simulink

Periodic CAN Message Transmission Behavior in Simulink

Set up periodic transmission and reception of CAN messages in Simulink® using MathWorks® virtual CAN channels. The virtual channels are connected in a loopback configuration.

Log and Replay CAN Messages

Log and Replay CAN Messages

Log and replay CAN messages using MathWorks® Virtual CAN channels in Simulink®. You can update this model to connect to supported hardware on your system.

Set Up Communication Between Host and Target Models

Set Up Communication Between Host and Target Models

Set up CAN communication between host-side CAN Vector blocks and target models. This example uses:

Implement CAN Network for Robotic Arm in Simulink

Implement CAN Network for Robotic Arm in Simulink

Use Vehicle Network Toolbox™ and Simulink to implement a Controller Area Network (CAN) in a remote manipulator arm.

Ports

Input

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This block has one input port, CAN Msg. The block takes the specified input CAN messages and unpacks their signal data to separate outputs.

The block supports the following signal data types: single, double, int8, int16, int32, int64, uint8, uint16, uint32, uint64, and boolean. The block does not support fixed-point data types.

Output

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The block has one output port by default. The number of output ports is dynamic and depends on the number of signals that you specify for the block to output. For example, if your message has four signals, the block can have four output ports.

For signals specified manually or by a CANdb, the default output data type for CAN signals is double. To specify other types, use a Signal Specification (Simulink) block. This allows the block to support the following output signal data types: single, double, int8, int16, int32, int64, uint8, uint16, uint32, uint64, and boolean. The block does not support fixed-point types.

Additional output ports can be added by selecting the options in the parameters Output ports pane. For more information, see the parameters Output identifier, Output timestamp, Output error, Output remote, Output length, and Output status.

Parameters

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  • raw data: Output data as a uint8 vector array. If you select this option, you specify only the message fields. The other signal parameter fields are unavailable. This option opens only one output port on your block.

    The conversion formula is:

    physical_value = raw_value * Factor + Offset
    where raw_value is the unpacked signal value and physical_value is the scaled signal value.

  • manually specified signals: You can specify data signals. If you select this option, use the Signals table to create your signals message manually. The number of output ports on your block depends on the number of signals that you specify. For example, if you specify four signals, your block has four output ports.

  • CANdb specified signals: You can specify a CAN database file that contains data signals. If you select this option, select a CANdb file. The number of output ports on your block depends on the number of signals specified in the CANdb file. For example, if the selected message in the CANdb file has four signals, your block has four output ports.

  • ARXML specified signals: Allows you to specify an ARXML file for signal definitions. This disables some remote options. After reading data from the ARXML file, you can switch to manually specified signals to further modify the table.

    For detailed information, see ARXML File Support for CAN in Simulink.

Programmatic Use

Block Parameter: DataFormat
Type: string | character vector
Values: 'raw data' | 'manually specified signals' | 'CANdb specified signals' | 'ARXML specified signals'
Default: 'raw data'

This option is available if you specify that your data is input via a CANdb file in the Data to be output as list. Click Browse to find the CANdb file on your system. The messages and signal definitions specified in the CANdb file populate the Message section of the dialog box. The signals specified in the CANdb file populate Signals table. File names that contain non-alphanumeric characters such as equal signs, ampersands, and so forth are not valid CAN database file names. You can use periods in your database name. Rename CAN database files with non-alphanumeric characters before you use them.

Programmatic Use

Block Parameter: CANdbFile
Type: string | character vector

This option is available if you specify in the Data to be output as list that your data is to be output as a CANdb file and you select a CANdb file in the CANdb file field. You can select the message that you want to view. The Signals table then displays the details of the selected message.

Programmatic Use

Block Parameter: MsgList
Type: string | character vector

Specify a name for your CAN message. The default is CAN Msg. This option is available if you choose to output raw data or manually specify signals.

Programmatic Use

Block Parameter: MsgName
Type: string | character vector

Specify whether your CAN message identifier is a Standard or an Extended type. The default is Standard. A standard identifier is an 11-bit identifier and an extended identifier is a 29-bit identifier. This option is available if you choose to output raw data or manually specify signals. For CANdb-specified signals, the Identifier type inherits the type from the database.

Programmatic Use

Block Parameter: MsgIDType
Type: string | character vector
Values: 'Standard (11-bit identifier)' | 'Extended (29-bit identifier)'
Default: 'Standard (11-bit identifier)'

Specify your CAN message ID. This number must be an integer from 0 through 2047 for a standard identifier and from 0 through 536870911 for an extended identifier. If you specify -1, the block unpacks the messages that match the length specified for the message. You can also specify hexadecimal values by using the hex2dec function. This option is available if you choose to output raw data or manually specify signals.

Programmatic Use

Block Parameter: MsgIdentifier
Type: string | character vector
Values: '0' to '536870911'

Specify the length of your CAN message from 0 to 8 bytes. If you are using CANdb specified signals for your output data, the CANdb file defines the length of your message. Otherwise, this field defaults to 8. This option is available if you choose to output raw data or manually specify signals.

Programmatic Use

Block Parameter: MsgLength
Type: string | character vector
Values: '0' to '8'
Default: '8'

Add a signal to the signal table.

Programmatic Use

None

Remove the selected signal from the signal table.

Programmatic Use

None

If you choose to specify signals manually or define signals by using a CANdb file, this table appears.

If you are using a CANdb file, the data in the file populates this table and you cannot edit the fields. To edit signal information, switch to specified signals.

If you have selected to specify signals manually, create your signals manually in this table. Each signal that you create has these values:

Name

Specify a descriptive name for your signal. The Simulink block in your model displays this name. The default is Signal [row number].

Start bit

Specify the start bit of the data. The start bit is the least significant bit counted from the start of the message. The start bit must be an integer from 0 through 63.

Length (bits)

Specify the number of bits the signal occupies in the message. The length must be an integer from 1 through 64.

Byte order

Select either of these options:

  • LE: Where the byte order is in little-endian format (Intel®). In this format you count bits from the least-significant bit to the most-significant bit. For example, if you pack one byte of data in little-endian format, with the start bit at 20, the data bit table resembles this figure.

    Little-Endian Byte Order Counted from the Least Significant Bit to the Highest Address

  • BE: Where the byte order is in big-endian format (Motorola®). In this format you count bits from the least-significant bit to the most-significant bit. For example, if you pack one byte of data in big-endian format, with the start bit at 20, the data bit table resembles this figure.

    Big-Endian Byte Order Counted from the Least Significant Bit to the Lowest Address

Data type

Specify how the signal interprets the data in the allocated bits. Choose from:

  • signed (default)

  • unsigned

  • single

  • double

Multiplex type

Specify how the block unpacks the signals from the CAN message at each time step:

  • Standard: The signal is unpacked at each time step.

  • Multiplexor: The Multiplexor signal or the mode signal is unpacked. You can specify only one Multiplexor signal per message.

  • Multiplexed: The signal is unpacked if the value of the Multiplexor signal (mode signal) at run time matches the configured Multiplex value of this signal.

For example, a message has four signals with these values.

Signal NameMultiplex TypeMultiplex Value
Signal-AStandardNot applicable
Signal-BMultiplexed1
Signal-CMultiplexed0
Signal-DMultiplexorNot applicable

In this example:

  • The block unpacks Signal-A (Standard signal) and Signal-D (Multiplexor signal) in every time step.

  • If the value of Signal-D is 1 at a particular time step, then the block unpacks Signal-B along with Signal-A and Signal-D in that time step.

  • If the value of Signal-D is 0 at a particular time step, then the block unpacks Signal-C along with Signal-A and Signal-D in that time step.

  • If the value of Signal-D is not 1 or 0, the block does not unpack either of the Multiplexed signals in that time step.

Multiplex value

This option is available only if you have selected the Multiplex type to be Multiplexed. The value you provide must match the Multiplexor signal value at run time for the block to unpack the Multiplexed signal. The Multiplex value must be a positive integer or zero.

Factor

Specify the Factor value applied to convert the unpacked raw value to the physical value (signal value). For more information, see the Data input as parameter conversion formula.

Offset

Specify the Offset value applied to convert the physical value (signal value) to the unpacked raw value. For more information, see the Data input as parameter conversion formula.

Min, Max

Define a range of raw signal values. The default settings are -Inf (negative infinity) and Inf, respectively. For CANdb specified signals, these settings are read from the CAN database. For manually specified signals, you can specify the minimum and maximum physical value of the signal. By default, these settings do not clip signal values that exceed them.

Programmatic Use

Block Parameter: SignalInfo
Type: string | character vector

Select this option to output a CAN message identifier. The data type of this port is uint32.

Programmatic Use

Block Parameter: IDPort
Type: string | character vector
Values: 'off' | 'on'
Default: 'off'

Select this option to output the message timestamp. This value indicates when the message was received, measured as the number of seconds elapsed since the model simulation began. This option adds a new output port to the block. The data type of this port is double.

Programmatic Use

Block Parameter: TimestampPort
Type: string | character vector
Values: 'off' | 'on'
Default: 'off'

Select this option to output the message error status. This option adds a new output port to the block. An output value of 1 on this port indicates that the incoming message is an error frame. If the output value is 0, there is no error. The data type of this port is uint8.

Programmatic Use

Block Parameter: ErrorPort
Type: string | character vector
Values: 'off' | 'on'
Default: 'off'

Select this option to output the message remote frame status. This option adds a new output port to the block. The data type of this port is uint8.

Programmatic Use

Block Parameter: RemotePort
Type: string | character vector
Values: 'off' | 'on'
Default: 'off'

Select this option to output the length of the message in bytes. This option adds a new output port to the block. The data type of this port is uint8.

Programmatic Use

Block Parameter: LengthPort
Type: string | character vector
Values: 'off' | 'on'
Default: 'off'

Select this option to output the message received status. The status is 1 if the block receives a new message and 0 if it does not. This option adds a new output port to the block. The data type of this port is uint8.

Programmatic Use

Block Parameter: StatusPort
Type: string | character vector
Values: 'off' | 'on'
Default: 'off'

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2009a

See Also

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