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

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

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 toInherit: Inherit via internal rule and select theRequire all data port inputs to have the same data type check box.

Tip

For back propagation Inherit: Inherit via internal rule, theRequire all data port inputs to have the same data type parameter must be selected. Otherwise, the block does not automatically back propagate the output data type to the first and third output ports.

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 toerror. 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, theThreshold 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

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 | image

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

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

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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 | image

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 theCriteria 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 supportu2 ~= 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

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 thanOutput 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

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

Programmatic Use

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 inputs to have the same data type.

Programmatic Use

Specify the output data type.

Inherit: Inherit via internal rule

Uses the following rules to determine the output data type.

Inherit: Inherit via back propagation

Adopts the data type from the output block.

Inherit: Inherit same as first input

Uses data type of the first data input port.

double

Specifies output data type isdouble.

single

Specifies output data type issingle.

half

Specifies output data type ishalf.

int8

Specifies output data type isint8.

uint8

Specifies output data type isuint8.

int16

Specifies output data type isint16.

uint16

Specifies output data type isuint16.

int32

Specifies output data type isint32.

uint32

Specifies output data type isuint32.

int64

Specifies output data type isint64.

uint64

Specifies output data type isuint64.

fixdt(1,16,0)

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

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

Specifies output data type is fixed pointfixdt(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

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

Choose one of these rounding modes.

Ceiling

Rounds both positive and negative numbers toward positive infinity. Equivalent to the MATLABceil 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 MATLABfloor function.

Nearest

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

Programmatic Use

See Also

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

Specify whether overflows saturate or wrap.

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

For example, the maximum value that the signed 8-bit integer int8 can represent is 127. Any block operation result greater than this maximum value causes overflow of the 8-bit integer.

• With this parameter selected, the block output saturates at 127. Similarly, the block output saturates at a minimum output value of -128.
• With this parameter cleared, the software interprets the overflow-causing value as int8, which can produce an unintended result. For example, a block result of 130 (binary 1000 0010) expressed asint8 is -126.

Tips

• Consider selecting this parameter when your model has a possible overflow and you want explicit saturation protection in the generated code.
• Consider clearing this parameter when you want to optimize efficiency of your generated code. Clearing this parameter 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 parameter, 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

To set the block parameter value programmatically, use the set_param function.

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 Characteristics

Extended Capabilities

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

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

Complex Data Support

This block supports code generation for complex signals.

Version History

Introduced before R2006a