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 (Simulink) 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 (Simulink); 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 orContinuous
for a continuous-time signal.- Output
Specify whether the output is
Sample-based (interpret vectors as 1-D)
,Sample-based
, orFrame-based
. When you selectSample-based
and the output is a vector, its dimension is constrained to match the Constant value dimension (row or column). When you selectSample-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 selectDiscrete
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
fixdt
(Simulink) function. This parameter is only visible when you selectUser-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 selectUser-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
orUser-defined
for the Output data type parameter andUser-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
Constant (Simulink) | Simulink |
Signal From Workspace | DSP System Toolbox |
Version History
Introduced in R2008b