Switch

Switch output between first input and third input based on value of second input

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Libraries:
Simulink / Commonly Used Blocks
Simulink / Signal Routing
HDL Coder / Commonly Used Blocks
HDL Coder / Signal Routing

Description

Types of Block Inputs

The Switch block passes through the first input or the third input based on the value of the second input. The first and third inputs are called data inputs. The second input is called the control input. Specify the condition under which the block passes the first input by using the Criteria for passing first input and Threshold parameters.

To immediately back propagate a known output data type to the first and third input ports, set the Output data type parameter to Inherit: Inherit via internal rule and select the Require all data port inputs to have the same data type check box.

Limitations on Data Inputs

The sizes of the two data inputs can be different if you select Allow different data input sizes. However, this block does not support variable-size input signals. Therefore, the size of each input cannot change during simulation.

If the data inputs to the Switch block are buses, the element names of both buses must be the same. Using the same element names ensures that the output bus has the same element names no matter which input bus the block selects. To ensure that your model meets this requirement, use a bus object to define the buses and set the Element name mismatch diagnostic to error. For more information, see Model Configuration Parameters: Connectivity Diagnostics.

Block Icon Appearance

The block icon helps you identify Criteria for passing first input and Threshold without having to open the block dialog box.

For information about port order for various block orientations, see Identify Port Location on Rotated or Flipped Block.

Block Behavior for Boolean Control Input

When the control input is a Boolean signal, use one of these combinations of criteria and threshold value:

• u2 >= Threshold, where the threshold value equals 1

• u2 > Threshold, where the threshold value equals 0

• u2 ~=0

Otherwise, the Switch block ignores the threshold and uses the Boolean input for signal routing. For a control input of 1, the block passes the first input, and for a control input of 0, the block passes the third input. In this case, the block icon changes after compile time and uses T and F to label the first and third inputs, respectively.

Data Type Support

The control input can be of any data type that Simulink^® supports, including fixed-point and enumerated types. The control input cannot be complex. If the control input is enumerated, the Threshold parameter must be a value of the same enumerated type.

The data inputs can be of any data type that Simulink supports. If either data input is of an enumerated type, the other must be of the same enumerated type.

When the output is of enumerated type, both data inputs should use the same enumerated type as the output.

For more information, see Data Types Supported by Simulink.

Examples

Switch Block with a Boolean Control Port Example

A Switch block with a Boolean input for the control port.

Open Script

Model a Fault-Tolerant Fuel Control System

Combine Stateflow® with Simulink® to efficiently model hybrid systems. This type of modeling is particularly useful for systems that have numerous possible operational modes based on discrete events. Traditional signal flow is handled in Simulink while changes in control configuration are implemented in Stateflow. The model described below represents a fuel control system for a gasoline engine. The system is highly robust in that individual sensor failures are detected and the control system is dynamically reconfigured for uninterrupted operation.

Open Model

Accurate Zero-Crossing Detection

How zero crossings work in Simulink®. In this model, three shifted sine waves are fed into an absolute value block and saturation block. At exactly t = 5, the output of the switch block changes from the absolute value to the saturation block. Zero crossings in Simulink will automatically detect exactly when the switch block changes its output, and the solver will step to the exact time that the event happens. This can be seen by examining the output in the scope.

Open Model

Ports

Input

Port_1 — First data input signal

scalar | vector

First of two data inputs. The block propagates either the first or second data input to the output. The block selects which input to pass based on the control input. Specify the condition for the control input to pass the first input using the Criteria for passing first input and Threshold parameters.

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

Port_2 — Control input signal

scalar | vector

Control signal the block uses to determine whether to pass the first or second data input to the output. If the control input meets the condition set in the Criteria for passing first input parameter, then the block passes the first data input. Otherwise, the block passes the second data input.

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

Port_3 — Second data input signal

scalar | vector

Second of two data inputs. The block propagates either the first or second data input to the output. The block selects which input to pass based on the control input. Specify the condition for the control input to pass the first or second input using the Criteria for passing first input and Threshold parameters.

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

Output

Port_1 — Output signal

scalar | vector

Output signal propagated from either the first or second input signal, based on the control signal value.

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

Parameters

Main

Criteria for passing first input — Selection criteria to pass first data input

u2 > Threshold (default) | u2 >= Threshold | u2 ~= 0

Select the condition under which the block passes the first data input. If the control input meets the condition set in the Criteria for passing first input parameter, the block passes the first input. Otherwise, the block passes the second data input signal from input Port_3.

u2 >= Threshold

Checks whether the control input is greater than or equal to the threshold value.

u2 > Threshold

Checks whether the control input is greater than the threshold value.

u2 ~= 0

Checks whether the control input is nonzero.

Note

The Switch block does not support u2 ~= 0 mode for enumerated data types.

Tip

When the control input is a Boolean signal, use one of these combinations of condition and threshold value:

• u2 >= Threshold, where the threshold value equals 1

• u2 > Threshold, where the threshold value equals 0

• u2 ~= 0

Otherwise, the Switch block ignores threshold values and uses the Boolean value for signal routing. For a value of 1, the block passes the first input, and for a value of 0, the block passes the third input. A warning message that describes this behavior also appears in the MATLAB^® Command Window.

Programmatic Use

Block Parameter: Criteria

Type: character vector

Value: 'u2 >= Threshold' | 'u2 > Threshold' | 'u2 ~= 0'

Default: 'u2 > Threshold'

Threshold — Threshold used in criteria

0 (default) | scalar

Assign the threshold used in the Criteria for passing first input that determines which input the block passes to the output. Threshold must be greater than Output minimum and less than Output maximum.

To specify a nonscalar threshold, use brackets. For example, the following entries are valid:

• [1 4 8 12]

• [MyColors.Red, MyColors.Blue]

Dependencies

Setting Criteria for passing first input to u2 ~= 0 disables this parameter.

Programmatic Use

Block Parameter: Threshold

Type: character vector

Value: scalar

Default: '0'

Enable zero-crossing detection — 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 | string

Values: 'off' | 'on'

Default: 'on'

Signal Attributes

The Data Type Assistant helps you set data attributes. To use the Data Type Assistant, click . For more information, see Specify Data Types Using Data Type Assistant.

Require all data port inputs to have the same data type — Require data ports to have the same data type

off (default) | on

Require all data inputs to have the same data type.

Programmatic Use

Block Parameter: InputSameDT

Type: character vector

Value: 'off' | 'on'

Default: 'off'

Output minimum — Minimum output value for range checking

[] (default) | scalar

Lower value of the output range that Simulink checks.

Simulink uses the minimum to perform:

• Parameter range checking (see Specify Minimum and Maximum Values for Block Parameters) for some blocks.

• Simulation range checking (see Specify Signal Ranges and Enable Simulation Range Checking).

• Automatic scaling of fixed-point data types.

• Optimization of the code that you generate from the model. This optimization can remove algorithmic code and affect the results of some simulation modes such as SIL or external mode. For more information, see Optimize using the specified minimum and maximum values (Embedded Coder).

Note

Output minimum does not saturate or clip the actual output signal. Use the Saturation block instead.

Programmatic Use

Block Parameter: OutMin

Type: character vector

Values: '[ ]'| scalar

Default: '[ ]'

Output maximum — Maximum output value for range checking

[] (default) | scalar

Upper value of the output range that Simulink checks.

Simulink uses the maximum value to perform:

• Parameter range checking (see Specify Minimum and Maximum Values for Block Parameters) for some blocks.

• Simulation range checking (see Specify Signal Ranges and Enable Simulation Range Checking).

• Automatic scaling of fixed-point data types.

• Optimization of the code that you generate from the model. This optimization can remove algorithmic code and affect the results of some simulation modes such as SIL or external mode. For more information, see Optimize using the specified minimum and maximum values (Embedded Coder).

Note

Output maximum does not saturate or clip the actual output signal. Use the Saturation block instead.

Programmatic Use

Block Parameter: OutMax

Type: character vector

Values: '[ ]'| scalar

Default: '[ ]'

Output data type — Output data type

Inherit: Inherit via internal rule (default) | Inherit: Inherit via back propagation | Inherit: Same as first input | double | single | half | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | fixdt(1,16) | fixdt(1,16,0) | fixdt(1,16,2^0,0) | string | Enum: <class name> | <data type expression> | Simulink.ImageType(480,640,3)

Specify the output data type.

Inherit: Inherit via internal rule

Uses the following rules to determine the output data type.

Data Type of First Input Port	Output Data Type
Has a larger positive range than the third input port	Inherited from the first input port
Has the same positive range as the third input port	Inherited from the third input port
Has a smaller positive range than the third input port
Is a Boolean value and third input port is uint8
Is uint8 and third input port is a Boolean value
Is a Boolean value and other is int8	Set to a Boolean value
Is uint8 and other is a Boolean value

Data Types of Two Input Ports	Output Data Type
Has one input type as a Boolean value and another as uint8	Set to data type of the third data port
Has one input as a Boolean value and another as int8	Set to a Boolean value

Inherit: Inherit via back propagation

Uses data type of the driving block.

Inherit: Inherit same as first input

Uses data type of the first data input port.

double

Specifies output data type is double.

single

Specifies output data type is single.

half

Specifies output data type is half.

int8

Specifies output data type is int8.

uint8

Specifies output data type is uint8.

int16

Specifies output data type is int16.

uint16

Specifies output data type is uint16.

int32

Specifies output data type is int32.

uint32

Specifies output data type is uint32.

int64

Specifies output data type is int64.

uint64

Specifies output data type is uint64.

fixdt(1,16,0)

Specifies output data type is fixed point fixdt(1,16,0).

fixdt(1,16,2^0,0)

Specifies output data type is fixed point fixdt(1,16,2^0,0).

Enum: <class name>

Uses an enumerated data type, for example, Enum: BasicColors.

Simulink.ImageType(480,640,3)

Uses a Simulink.ImageType (Computer Vision Toolbox) object if you have Computer Vision Toolbox™.

string

Specifies output data type is string.

<data type expression>

Uses a data type object, for example, Simulink.NumericType.

Tip

When the output is of enumerated type, both data inputs should use the same enumerated type as the output.

Programmatic Use

Block Parameter: OutDataTypeStr

Type: character vector

Values: 'Inherit: Inherit via internal rule | 'Inherit: Inherit via back propagation' | 'Inherit: Same as first input' | 'double' | 'single' | 'half' | 'int8' | 'uint8' | 'int16' | 'uint16', 'int32' | 'uint32' | 'int64' | 'uint64' | 'fixdt(1,16)' | 'fixdt(1,16,0)' | 'fixdt(1,16,2^0,0)' | Enum: <class name> | Simulink.ImageType(480,640,3) | 'string' | '<data type expression>'

Default: 'Inherit: Inherit via internal rule'

Lock data type settings against changes by the fixed-point tools — Prevent fixed-point tools from overriding data types

off (default) | on

Select this parameter to prevent the fixed-point tools from overriding the data types you specify on this block. For more information, see Lock the Output Data Type Setting (Fixed-Point Designer).

Programmatic Use

Block Parameter: LockScale

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Integer rounding mode — Specify the rounding mode for fixed-point operations

Floor (default) | Ceiling | Convergent | Nearest | Round | Simplest | Zero

Choose one of these rounding modes.

Ceiling

Rounds both positive and negative numbers toward positive infinity. Equivalent to the MATLAB ceil function.

Convergent

Rounds number to the nearest representable value. If a tie occurs, rounds to the nearest even integer. Equivalent to the Fixed-Point Designer™ convergent function.

Floor

Rounds both positive and negative numbers toward negative infinity. Equivalent to the MATLAB floor function.

Nearest

Rounds number to the nearest representable value. If a tie occurs, rounds toward positive infinity. Equivalent to the Fixed-Point Designer nearest function.

Round

Rounds number to the nearest representable value. If a tie occurs, rounds positive numbers toward positive infinity and rounds negative numbers toward negative infinity. Equivalent to the Fixed-Point Designer round function.

Simplest

Automatically chooses between round toward floor and round toward zero to generate rounding code that is as efficient as possible.

Zero

Rounds number toward zero. Equivalent to the MATLAB fix function.

Programmatic Use

Block Parameter: RndMeth

Type: character vector

Values: 'Ceiling' | 'Convergent' | 'Floor' | 'Nearest' | 'Round' | 'Simplest' | 'Zero'

Default: 'Floor'

See Also

For more information, see Rounding (Fixed-Point Designer).

Saturate on integer overflow — Method of overflow action

off (default) | on

Specify whether overflows saturate or wrap.

• off — Overflows wrap to the appropriate value that the data type can represent.

  For example, the number 130 does not fit in a signed 8-bit integer and wraps to -126.

• on — Overflows saturate to either the minimum or maximum value that the data type can represent.

  For example, an overflow associated with a signed 8-bit integer can saturate to -128 or 127.

Tip

• Consider selecting this check box when your model has a possible overflow and you want explicit saturation protection in the generated code.

• Consider clearing this check box when you want to optimize efficiency of your generated code.

  Clearing this check box also helps you to avoid overspecifying how a block handles out-of-range signals. For more information, see Troubleshoot Signal Range Errors.

• When you select this check box, saturation applies to every internal operation on the block, not just the output or result.

• In general, the code generation process can detect when overflow is not possible. In this case, the code generator does not produce saturation code.

Programmatic Use

Block Parameter: SaturateOnIntegerOverflow

Type: character vector

Values: 'off' | 'on'

Default: 'off'

Allow different data input sizes — Allow different data input sizes

off (default) | on

Select this check box to allow input signals with different sizes. The block propagates the input signal size to the output signal. If the two data inputs are variable-size signals, the maximum size of the signals can be equal or different.

Programmatic Use

Block Parameter: AllowDiffInputSizes

Type: character vector

Value: 'on' | 'off'

Default: 'off'

Block Characteristics

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

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

Generated code relies on memcpy or memset functions (string.h) under certain conditions.

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

ConstrainedOutputPipeline	Number of registers to place at the outputs by moving existing delays within your design. Distributed pipelining does not redistribute these registers. The default 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 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 is 0. For more details, see OutputPipeline (HDL Coder).

Complex Data Support

This block supports code generation for complex signals.

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