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Byte Packing

Construct data frames

  • Byte Packing block

Simulink Real-Time / Utilities


The Byte Packing block converts one or more signals of user-selectable data types to a single vector of varying data types. The output of this block typically connects to an input port of a Send block.

The Byte Packing block and the Byte Unpacking block support the Simulink® Real-Time™ STF code generation targets and generate code that runs on Speedgoat target machines. Due to considerations such as endianness and addressable word size, these blocks can generate incorrect results for other code generation targets or target computers.

For example, suppose that you are packing three signals into a vector of uint8. The signals have the following attributes:

  1. Set the packed output port data type to uint8.

  2. Set the input port data type to a cell array encoding the data types:

    {'single', ['uint8'], ['uint8']}

    Use square brackets to represent vectors.

  3. Set the byte alignment value to 1.

  4. Connect the signals to the Byte Packing block.



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The block has from 1 to N input ports. Specify the number of input ports and their types by entering them as a cell array in the parameter Input port (unpacked) data types (cell array).

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean


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The block displays one output port that transmits a vector of packed data. You determine the data type of the packed data by setting Output port (packed) data type.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean


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From the list, select a data type for the output port.

Programmatic Use

Block Parameter: MaskPackedDataType

Specify as a cell array the data types of the input ports (unpacked) for the different input signals. The number of elements in the cell array determines the number of input ports shown by this block instance. To represent vector elements, use square brackets in the cell array.

Programmatic Use

Block Parameter: MaskUnpackedDataTypes

Each element in the input signals list starts at a multiple of the alignment value, specified from the start of the vector. If the alignment value is larger than the size of the data type in bytes, the block fills the space with pad bytes of value 0.

For example, if the alignment value is 4:

  • uint32 receives no padding

  • uint16 receives 2 bytes of padding

  • uint8 receives 3 bytes of padding

If the model accesses the data items frequently, consider selecting an alignment value equal to the largest data type that you want to access. If the model transfers data items frequently as a group, consider an alignment value of 1, which packs the data into as small a space as possible.

Programmatic Use

Block Parameter: MaskAlignment

Extended Capabilities

Version History

Introduced in R2006a