Switch
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 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 equals1
u2 > Threshold
, where the threshold value equals0
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.
Model Fault-Tolerant Fuel Control System
Combine Stateflow® and Simulink® capabilities to 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 in this example represents a fuel control system for a gasoline engine. The system is robust in that it detects individual sensor failures, and the control system is dynamically reconfigured for uninterrupted operation.
Accurate Zero-Crossing Detection
How zero-crossing detection works in Simulink®. Simulink uses zero-crossing detection to accurately simulate an abrupt model change or discontinuity without decreasing the solver time steps. For more information, see Zero-Crossing Detection.
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 1u2 > Threshold
, where the threshold value equals 0u2 ~= 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 the software checks.
The software 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).
Tips
Output minimum does not saturate or clip the actual output signal. Use the Saturation block instead.
Programmatic Use
To set the block parameter value programmatically, use
the set_param
function.
Parameter: | OutMin |
Values: | '[]' (default) | scalar in quotes |
Output maximum — Maximum output value for range checking
[]
(default) | scalar
Upper value of the output range that the software checks.
The software 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).
Tips
Output maximum does not saturate or clip the actual output signal. Use the Saturation block instead.
Programmatic Use
To set the block parameter value programmatically, use
the set_param
function.
Parameter: | OutMax |
Values: | '[]' (default) | scalar in quotes |
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 valueIs a Boolean value and other is int8
Set to a Boolean value Is uint8
and other is a Boolean valueData 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 Modes (Fixed-Point Designer).
Saturate on integer overflow — Method of overflow action
off
(default) | on
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.
Parameter: | SaturateOnIntegerOverflow |
Values: | 'off' (default) | 'on' |
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 |
|
Direct Feedthrough |
|
Multidimensional Signals |
|
Variable-Size Signals |
|
Zero-Crossing Detection |
|
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.
This block has one default HDL architecture.
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
|
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
|
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
|
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
See Also
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