Compare To Constant

R2026b

Determine how signal compares to specified constant

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Compare To Constant block

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Libraries:
Simulink / Logic and Bit Operations
HDL Coder / Logic and Bit Operations

Description

The Compare To Constant block compares an input signal to a constant. Specify the constant in the Constant value parameter. Specify how the input is compared to the constant value with the Operator parameter.

Examples

Exploring Law of Large Numbers Using MATLAB System Block

Use MATLAB System blocks to illustrate the law of large numbers in Simulink.

• Open Model

Ports

Input

Port_1 — Input signal

scalar | vector | matrix

Input signal, specified as a scalar, vector, or matrix, is compared with constant. The block first converts its Constant value parameter to the input data type, and then performs the specified operation.

Data Types: half | single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | enumerated | bus

Output

Port_1 — Output signal

0 | 1 | vector | matrix

The output is 0 if the comparison is false, and 1 if it is true.

Data Types: uint8 | Boolean

Parameters

Operator — Logical operator

<= (default) | == | ~= | < | >= | >

This parameter can have these values:

• == — Determine whether the input is equal to the specified constant.

• ~= — Determine whether the input is not equal to the specified constant.

• < — Determine whether the input is less than the specified constant.

• <= — Determine whether the input is less than or equal to the specified constant.

• > — Determine whether the input is greater than the specified constant.

• >= — Determine whether the input is greater than or equal to the specified constant.

Programmatic Use

Block Parameter: relop

Type: character vector

Values: '==' | '~='| '<' |'<='| '>='| '>'

Default: '<='

Constant value — Constant to compare with

constant

Specify the constant value to which the input is compared.

Programmatic Use

Block Parameter: const

Type: character vector

Value: scalar | vector | matrix | N-D array

Default: '3.0'

Output data type — Data type of the output

boolean (default) | uint8

Specify the data type of the output, boolean or uint8.

Programmatic Use

Block Parameter: OutDataTypeStr

Type: character vector

Values:'boolean' | 'uint8'

Default: 'boolean'

Enable zero-crossing detection — Select to enable zero-crossing detection

'on' (default) | 'off'

Select to enable zero-crossing detection. For more information, see Zero-Crossing Detection.

Programmatic Use

Block Parameter: ZeroCross

Type: character vector

Values: 'off' | 'on'

Default: 'on'

Block Characteristics

Data Types	Boolean | double | enumerated | fixed point | half | integer | single
Direct Feedthrough	yes
Multidimensional Signals	yes
Variable-Size Signals	yes
Zero-Crossing Detection	yes

More About

Model Coverage

If you have a Simulink^® Coverage™ license, the Compare To Constant block receives condition coverage.

Condition coverage measures:

• The number of times that the comparison between the input and the specified constant is true

• The number of times that the comparison between the input and the specified constant is false

If you select the Relational boundary (Simulink Coverage) coverage metric, the Compare To Constant block receives relational boundary coverage. For more information, see Relational Boundary Coverage (Simulink Coverage).

Extended Capabilities

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

HDL Code Generation

Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.

HDL Coder™ provides additional configuration options that affect HDL implementation and synthesized logic.

HDL Architecture

This block has one default HDL architecture.

HDL Block Properties

General

HDL Property	Description
ConstrainedOutputPipeline	Number of registers to place at the outputs by moving existing delays in the design. Distributed pipelining does not redistribute these registers. The default value is 0. For more details, see ConstrainedOutputPipeline (HDL Coder).
InputPipeline	Number of input pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default value is 0. For more details, see InputPipeline (HDL Coder).
OutputPipeline	Number of output pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default value is 0. For more details, see OutputPipeline (HDL Coder).
SynthesisAttributes	Specifies the synthesis attributes for the blocks and block output signals in the model. The generated HDL code contains these attributes. For more information, see SynthesisAttributes (HDL Coder).

Data Type Support

This table lists the data types that the input port supports for HDL code generation:

Input Port	Dimensions	Fixed-Point Values	Floating-Point Values	Built-in Integers	Bus Signals	Boolean Values	Complex Values
Port_1	Scalar Vector Matrices up to two dimensions	Yes	Half Single Double	Yes	No	No	Yes

The output port outputs data type uint8 or boolean, depending on the value of the Output data type parameter.

To generate HDL code when using native floating-point input data types, open the HDL Code Generation > Floating-Point pane in the Configuration Parameters dialog box and select the Use floating-point parameter. For more information, see Generate Target-Independent HDL Code with Native Floating-Point (HDL Coder).

Native Floating-Point Latency

When you use half, single, or double data types as inputs to the block, you can use the Latency Strategy (HDL Coder) model configuration parameter to specify whether the blocks latency maps to minimum or maximum latency values when using native floating-point libraries. The block supports these native floating-point latency values:

Floating-Point Data Type	Latency Strategy Setting	Latency Cycles	Custom Latency Support
double	MIN	1	No
	MAX	3
single	MIN	1	No
	MAX	3
half	MIN	1	No
	MAX	2

The block uses multicycle implementations to introduce additional latency in the generated code. To see the added latency, view the generated model or validation model. See Generated Model and Validation Model (HDL Coder).

Optimizations

You can use these HDL Coder optimizations to optimize the speed, area, and I/Os.

Area Optimization

Optimization	Description
Resource Sharing (HDL Coder)	Resource sharing is an area optimization in which HDL Coder identifies multiple functionally equivalent resources and replaces them with a single resource.
Streaming (HDL Coder)	Streaming is an area optimization in which HDL Coder transforms a vector data path to a scalar data path or to several smaller-sized vector data paths.

Speed Optimization

Optimization	Description
Specify Distributed Pipelining Settings (HDL Coder)	Distributed pipelining, or register retiming, is a speed optimization that moves existing delays in a design to reduce the critical path while preserving functional behavior.
Clock-Rate Pipelining (HDL Coder)	Clock-rate pipelining is an optimization framework that allows other speed and area optimizations to introduce latency at the clock rate.
Specify Adaptive Pipelining Settings (HDL Coder)	Adaptive pipelining optimization creates patterns or combination of blocks with registers that can improve the achievable clock frequency and reduce the area usage on the FPGA boards by inserting pipeline registers to the blocks in your design.
Critical Path Estimation (HDL Coder)	To quickly identify the most likely critical path in your design, use critical path estimation. Critical path estimation speeds up the iterative process of finding the critical path. To know blocks that are characterized in critical path estimation, see Characterized Blocks (HDL Coder).

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

Fixed-Point Conversion
Design and simulate fixed-point systems using Fixed-Point Designer™.

Version History

Introduced before R2006a

R2026b: Generate HDL code when using native floating-point and optimizations

You can now generate synthesizable HDL code for the Compare To Constant block when using native floating-point data types, including half, single, or double.

You can also use various HDL optimizations, such as distributed pipelining, hierarchy flattening, or delay balancing to generate optimized HDL code for the block.

R2026a: Specify synthesis attributes for blocks and block output signals

Use the SynthesisAttributes HDL block property to specify the synthesis attributes for the block and its output signals. HDL Coder includes these attributes in the generated HDL code.