Switch

Combine multiple signals into single signal

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  • Library:

  • Simulink / Commonly Used Blocks

    Simulink / Signal Routing

    HDL Coder / Commonly Used Blocks

    HDL Coder / Signal Routing

  • Switch block

Description

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

Bus Support

The Switch block is a bus-capable block. The data inputs can be virtual or nonvirtual bus signals subject to the following restrictions:

  • All the buses must be equivalent (same hierarchy with identical names and attributes for all elements).

  • All signals in a nonvirtual bus input to a Switch block must have the same sample time. The requirement holds even if the elements of the associated bus object specify inherited sample times.

You can use a Rate Transition block to change the sample time of an individual signal, or of all signals in a bus. See Modify Sample Times for Nonvirtual Buses and Bus-Capable Blocks for more information.

You can use an array of buses as an input signal to a Switch block. For details about defining and using an array of buses, see Combine Buses into an Array of Buses. When using an array of buses, set the Threshold parameter to a scalar value.

Limitations

  • 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. See Connectivity Diagnostics Overview for more information.

Ports

Input

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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

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

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

Output

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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

Parameters

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Main

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'

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: 'off' | '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

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the data type attributes. For more information, see Specify Data Types Using Data Type Assistant.

Require all data inputs to have the same data type.

Programmatic Use

Block Parameter: InputSameDT
Type: character vector
Value:
Default: '0'

Lower value of the output range that Simulink® checks.

Simulink uses the minimum to perform:

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: '[ ]'

Upper value of the output range that Simulink checks.

Simulink uses the maximum value to perform:

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: '[ ]'

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 PortOutput Data Type
Has a larger positive range than the third input portInherited from the first input port
Has the same positive range as the third input portInherited from the third input port
Has a smaller positive range than the third input port
Inherit: Inherit via back propagation

Uses data type of the driving block.

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.

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' | '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> | 'string' | '<data type expression>'
Default: 'Inherit: Inherit via internal rule'

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'

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).

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'

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'

Model Examples

Switch Block with a Boolean Control Port Example

Switch Block with a Boolean Control Port Example

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

Open Script
Modeling a Fault-Tolerant Fuel Control System

Modeling 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

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

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

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

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

See Also

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Introduced before R2006a

Simulink Documentation

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