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Extract Bits

Output selection of contiguous bits from input signal

  • Library:
  • Simulink / Logic and Bit Operations

    HDL Coder / Logic and Bit Operations

Description

The Extract Bits block allows you to output a contiguous selection of bits from the stored integer value of the input signal. Use the Bits to extract parameter to define the method for selecting the output bits.

  • Select Upper half to output the half of the input bits that contain the most significant bit. If there is an odd number of bits in the input signal, the number of output bits is given by the equation

    number of output bits = ceil(number of input bits/2)
  • Select Lower half to output the half of the input bits that contain the least significant bit. If there is an odd number of bits in the input signal, the number of output bits is given by the equation

    number of output bits = ceil(number of input bits/2)
  • Select Range starting with most significant bit to output a certain number of the most significant bits of the input signal. Specify the number of most significant bits to output in the Number of bits parameter.

  • Select Range ending with least significant bit to output a certain number of the least significant bits of the input signal. Specify the number of least significant bits to output in the Number of bits parameter.

  • Select Range of bits to indicate a series of contiguous bits of the input to output in the Bit indices parameter. You indicate the range in [start end] format, and the indices of the input bits are labeled contiguously starting at 0 for the least significant bit.

This block does not report wrap on overflow warnings during simulation. To report these warnings, see the Simulink.restoreDiagnostic reference page. The block does report errors due to wrap on overflow.

Ports

Input

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Input signal, specified as a scalar, vector, matrix, or N-D array. Floating-point inputs are passed through the block unchanged. boolean inputs are treated as uint8 signals.

Note

Performing bit operations on a signed integer is difficult. You can avoid difficulty by converting the data type of your input signals to unsigned integer types.

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

Output

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Contiguous selection of extracted bits, specified as a scalar, vector, matrix, or N-D array. Floating-point inputs are passed through the block unchanged.

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

Parameters

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Select the method for extracting bits from the input signal.

Consider an input signal that is represented in binary by 110111001:

  • If you select Upper half for the Bits to extract parameter, the output is 11011 in binary.

  • If you select Lower half for the Bits to extract parameter, the output is 11001 in binary.

  • If you select Range starting with most significant bit for the Bits to extract parameter, and specify 3 for the Number of bits parameter, the output is 110 in binary.

  • If you select Range ending with least significant bit for the Bits to extract parameter, and specify 8 for the Number of bits parameter, the output is 10111001 in binary.

  • If you select Range of bits for the Bits to extract parameter, and specify [4 7] for the Bit indices parameter, the output is 1011 in binary.

Programmatic Use

Block Parameter: bitsToExtract
Type: character vector
Values: 'Upper half' | 'Lower half' | 'Range starting with most significant bit' | 'Range ending with least significant bit' | 'Range of bits'
Default: 'Upper half'

Select the number of bits to output from the input signal. Signed integer data types must have at least two bits. Unsigned data integer types can be as short as a single bit.

Dependencies

To enable this parameter, set Bits to extract to Range starting with most significant bit or Range ending with least significant bit.

Programmatic Use

Block Parameter: numBits
Type: character vector
Values: positive integer
Default: '8'

Specify a contiguous range of bits of the input signal to output. Specify the range in [start end] format. The indices are assigned to the input bits starting with 0 at the least significant bit.

Dependencies

To enable this parameter, set Bits to extract to Range of bits.

Programmatic Use

Block Parameter: bitIdxRange
Type: character vector
Values: contiguous range
Default: '[0 7]'

Select the scaling mode to use on the output bit selection:

  • When you select Preserve fixed-point scaling, the fixed-point scaling of the input is used to determine the output scaling during the data type conversion.

  • When you select Treat bit field as an integer, the fixed-point scaling of the input is ignored, and only the stored integer is used to compute the output data type.

Programmatic Use

Block Parameter: outScalingMode
Type: character vector
Values: 'Preserve fixed-point scaling' | 'Treat bit field as an integer'
Default: 'Preserve fixed-point scaling'

Block Characteristics

Data Types

Boolean | double | fixed point | integer | single

Direct Feedthrough

no

Multidimensional Signals

no

Variable-Size Signals

no

Zero-Crossing Detection

no

Extended Capabilities

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

PLC Code Generation
Generate Structured Text code using Simulink® PLC Coder™.

Fixed-Point Conversion
Convert floating-point algorithms to fixed point using Fixed-Point Designer™.

Introduced before R2006a