Byte Unpack

Unpack 8-, 16-, or 32-bit input vector to multiple output vectors

  • Library:
  • Simulink Support Package for Arduino Hardware/Utilities

    Embedded Coder Support Package for STMicroelectronics Discovery Boards/Utilities

    Simulink Coder Support Package for STMicroelectronics Nucleo Boards/Utilities

    Embedded Coder Support Package for Texas Instruments C2000 Processors/Target Communication

Description

The Byte Unpack block converts a vector of uint8, uint16, or uint32 data type to one or more signals of user-selectable data types. This block is the inverse of the Byte Pack block. The input of this block connects to an output port of a receive block, such as SPI Receive, SCI Receive, or UDP Receive. The Receive block then transmits signals across various communication networks, such as SPI, SCI, UDP, or I2C.

Ports

Input

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Receives a vector of packed data.

Data Types: uint8 | uint16 | uint32

Output

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The block can have from 1 to N output ports, as specified by elements of the cell array in the parameter Output port data types (cell array).

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

Parameters

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Output port dimensions specified as a cell array of vectors.

Specify the same dimensions that you set for the corresponding Byte Pack block in the model.

Data types of the output ports (unpacked) specified for different output signals as a cell array. The number of elements in the cell array determines the number of output ports shown by this block instance.

Specify the same data types that you set in the Input port data types (cell array) parameter for the corresponding Byte Pack block in the model.

Each element in the input signals list starts at a multiple of the byte alignment value, specified from the start of the vector. If the byte alignment value is larger than the size of the data type in bytes, the output values are padded with zeros to fill the space allotted.

For example, if the byte alignment value is 4, a uint32 receives no padding, a uint16 receives 2 bytes of padding, and a uint8 receives 3 bytes of padding.

Choose the same byte alignment value that you set in the Byte alignment parameter for the corresponding Byte Pack block in the model.

Example

Suppose that you are unpacking a vector of data type uint8 or uint16, and the unpacked signals have these attributes.

DimensionSizeType
Vector3int8
Vector2int16
Scalar1uint8
Scalar1uint32

To unpack the signals:

  1. Set Output port dimensions (cell array) to:

    {'3’, ‘2’, ‘1’, ‘1’}

  2. Set Output port data types (cell array) to:

    {'int8’, ‘int16’, ‘uint8’, ‘uint32’}

    The block creates four output ports that match the order of the signal data types specified in the cell array.

  3. Set the required byte alignment value. The byte alignment value specifies the number of bytes after which a new byte starts from the previous boundary.

    The size of the output is based on the packed vector size, the byte alignment value, and the smallest memory cell size of the processor. Depending on the byte alignment value, output values padded with zeros are discarded before the next signal is unpacked. The smallest addressable memory cell indicates the number of bits occupied by char or uint8 data type for a processor, and determines the structure of packets.

  4. Connect incoming signals to the input port of the Byte Unpack block.

For processors with a smallest addressable memory cell of 8 bits per char, consider the packed input vector data type uint8.

Red zeros represent padded empty memory cells.

For a packed input vector of data type uint8 and byte alignment value 2, the int8 data value (23 04 FD) occupies three memory cells, with each cell occupying 8 bits. The next input signal of int16 data value (00DA FFF4) occupies the next four cells (fifth through eighth), and the fourth cell is empty (padded). The Byte Unpack block considers the alignment and padding of cells while unpacking.

The packed input vector of data type uint16 is:

The unpacked output signals are:

Unpacked Signals
DimensionSizeData TypeDec ValueHex Value
Vector3int83523
404
–3FD
Vector2int1621800DA
–12FFF4
Scalar1uint811270
Scalar1uint32500000001388

For processors such as Texas Instruments™ C2000™, with a smallest addressable memory cell of 16 bits per char, consider a packed input vector data type uint8. The output packet occupies 16 bits although the data value that the packet represents is 8 bits. The byte alignment values are calculated with respect to the 16-bit addressable memory.

For a packed input vector of data type uint8 and byte alignment value 2, the int8 data value (0023 0004 00FD) occupies three memory cells, with each cell occupying 16 bits. The next signal of data type int16 (00DA 0000 00F4 00FF) occupies the next four cells (fifth through eighth), and the fourth cell is empty (padded). The Byte Unpack block considers the alignment and padding of cells while unpacking.

For the packed input vector of data type uint16, the output packet occupies 16 bits, and the data value the packet represents is also 16 bits. For a packet size of 16 and larger, the byte alignment is calculated with respect to the number of bytes the data values have to be packed. Therefore, in this case, 1-byte alignment is not allowed.

For a packed input of data type uint16 and byte alignment value 2, the three int8 data values (0423 FD) occupy the first two memory cells. The fourth byte in the second memory cell is empty and padded with zero. The int16 data value (00DA FFF4) occupies the next two memory cells (third and fourth). The Byte Unpack block considers the alignment and padding of cells while unpacking.

The table lists the unpacked output signals. The int8 and uint8 data values occupy 16 bits, as indicated by the hex value.

Unpacked Signals
DimensionSizeData TypeDec ValueHex Value
Vector3int8350023
40004
–3FFFD
Vector2int1621800DA
–12FFF4
Scalar1uint81120070
Scalar1uint32500000001388

Introduced in R2016b