DSP Constant (Obsolete)

Generate discrete- or continuous-time constant signal

Library

Sources

dspobslib

Description

    Note   The DSP Constant block is still supported but is likely to be obsoleted in a future release. We strongly recommend replacing this block with the Constant block.

The DSP Constant block generates a signal whose value remains constant throughout the simulation. The Constant value parameter specifies the constant to output, and can be any valid MATLAB® expression that evaluates to a scalar, vector, or matrix.

When Sample mode is set to Continuous, the output is a continuous-time signal. When Sample mode is set to Discrete, the Sample time parameter is visible, and the signal has the discrete output period specified by the Sample time parameter.

You can set the output signal to Frame-based, Sample-based, or Sample-based (interpret vectors as 1-D) with the Output parameter.

Dialog Box

The Main pane of the DSP Constant block dialog box appears as follows.

Constant value

Specify the constant to generate. This parameter is Tunable; values entered here can be tuned, but their dimensions must remain fixed.

When you specify any data type information in this field, it is overridden by the value of the Output data type parameter in the Data Types pane, unless you select Inherit from 'Constant value'.

Sample mode

Specify the sample mode of the output, Discrete for a discrete-time signal or Continuous for a continuous-time signal.

Output

Specify whether the output is Sample-based (interpret vectors as 1-D), Sample-based, or Frame-based. When you select Sample-based and the output is a vector, its dimension is constrained to match the Constant value dimension (row or column). When you select Sample-based (interpret vectors as 1-D), however, the output has no specified dimensionality.

Sample time

Specify the discrete sample period for sample-based outputs. When you select Frame-based for the Output parameter, this parameter is named Frame period, and is the discrete frame period for the frame-based output. This parameter is only visible when you select Discrete for the Sample mode parameter.

The Data Types pane of the DSP Constant block dialog box appears as follows.

Output data type

Specify the output data type in one of the following ways:

  • Choose one of the built-in data types from the list.

  • Choose Fixed-point to specify the output data type and scaling in the Signed, Word length, Set fraction length in output to, and Fraction length parameters.

  • Choose User-defined to specify the output data type and scaling in the User-defined data type, Set fraction length in output to, and Fraction length parameters.

  • Choose Inherit from 'Constant value' to set the output data type and scaling to match the values of the Constant value parameter in the Main pane.

  • Choose Inherit via back propagation to set the output data type and scaling to match the following block.

The value of this parameter overrides any data type information specified in the Constant value parameter in the Main pane, except when you select Inherit from 'Constant value'.

Signed

Select to output a signed fixed-point signal. Otherwise, the signal is unsigned. This parameter is only visible when you select Fixed-point for the Output data type parameter.

Word length

Specify the word length, in bits, of the fixed-point output data type. This parameter is only visible when you select Fixed-point for the Output data type parameter.

User-defined data type

Specify any built-in or fixed-point data type. You can specify fixed-point data types using the following Fixed-Point Designer™ functions: sfix, ufix, sint, uint, sfrac, and ufrac. This parameter is only visible when you select User-defined for the Output data type parameter.

Set fraction length in output to

Specify the scaling of the fixed-point output by either of the following two methods:

  • Choose Best precision to have the output scaling automatically set such that the output signal has the best possible precision.

  • Choose User-defined to specify the output scaling in the Fraction length parameter.

This parameter is only visible when you select Fixed-point for the Output data type parameter, or when you select User-defined and the specified output data type is a fixed-point data type.

Fraction length

For fixed-point output data types, specify the number of fractional bits, or bits to the right of the binary point. This parameter is only visible when you select Fixed-point or User-defined for the Output data type parameter and User-defined for the Set fraction length in output to parameter.

Supported Data Types

  • Double-precision floating point

  • Single-precision floating point

  • Fixed point

  • Boolean

  • 8-, 16-, and 32-bit signed integers

  • 8-, 16-, and 32-bit unsigned integers

See Also

ConstantSimulink
Signal From WorkspaceDSP System Toolbox

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