Constant - 2022.1 English

Vitis Model Composer User Guide (UG1483)

Document ID
Release Date
2022.1 English

Provides constant value as a source.




The Constant block generates a constant output of the value specified by the Constant value parameter. If you select Interpret vector parameters as 1-D parameter and specify the constant value as a scalar, row matrix, or column matrix, then the output is a 1-D array. Otherwise, the output is always two-dimensional. The Constant block supports real or complex constant values.

Data Type Support

By default, the Constant block outputs a signal with double data type and the same complexity as the Constant value parameter. However, you can specify the output to be any data type that Model Composer supports, including fixed-point and half data types by selecting the Output data type parameter.


Constant value

The Constant value parameter specifies the constant value output of the block.

You can enter any expression that MATLABĀ® evaluates as a scalar or matrix.

Table 1. Settings
Choices Description
1.0 Constant Value
Interpret vector parameters as 1-D
Specifies whether the constant value should be interpreted as a 1-D array.
Table 2. Settings
Choices Description
On If the specified constant value is a scalar, row matrix, or column matrix, then the output is a 1-D array. Otherwise, the output is a 2-D matrix.
Off The output is a 2-D scalar or matrix.
Sample time

Specifies block sample time as a numerical value. The sample time of a block indicates when, during simulation, the block generates outputs or updates its internal state.

The block allows you to specify a block sample time directly as a numerical value. For example, to generate output at every two seconds, you can directly set the discrete sample time by specifying the numerical value of 2 as the Sample time parameter.

Settings for Sample time are:

Table 3. Sample Time Parameter
Sample Time Type Sample Time Supported Description Supported?
Discrete Ts

Generates output at discrete samples Ts.

Discrete sample time is supported with the initial time offset value fixed to 0. The initial offset value is not configurable.

Continuous 0 Generate output continuously by dividing the sample hits into major time steps and minor time steps. The Simulink ODE solver you choose integrates all continuous states from the simulation start time to a given major or minor time step. No
Inherited -1

The sample time value is inherited from other sources. It is determined by applying a set of heuristics and based on the context of the block within the model by Simulink.

Allowing a design to inherit sample time maximizes its reuse potential. For example, a design might fix the data types and dimensions of all its input and output signals. But you could reuse the design with different sample times (for example, discrete at 0.1 or discrete at 0.2, triggered, and so on).

Constant inf Constant sample time. Same as inherited sample time for HLS blocks. Yes
Variable -2 Variable Sample time. No
Triggered -1 (implicit) Execute the block upon some implicit condition when it is inside a subsystem like triggered, function call, or iterator subsystem. Yes

For additional details for simulating sample time, see Types of Sample time in the Simulink documentation.

Output data type

This parameter specifies the data type of the output signal.

If the output data type is one of the integer types, then the Constant value is rounded off as explained below.

A value with the fractional part less than 0.5 is rounded towards zero, the fractional part more than 0.5 is rounded away from zero.

In case of a tie (fractional part is 0.5), the Constant value is rounded up, i.e. the negative Constant value, is rounded towards zero and the positive Constant value is rounded away from zero.


The following data types are supported:

Table 4. Output Data Type Parameter
Setting Description
double, single, and half Floating point data types.
int8, uint8, int16, uint16, int32, uint32 Signed and unsigned integer data types.
Logical Boolean data type.
Fixed point data type
  • Fixed-point arithmetic data type with configurable output data type attributes like signedness, word length, fractional length.
  • Constant value conversion attributes rounding and overflow for reading constant value parameter.
Data type Expression

A string that specifies the output data type. See "Working with Data Type Expression" in the Vitis Model Composer User Guide (UG1483).