If Action Subsystem

Subsystem whose execution is enabled by If block

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Library:
Simulink / Ports & Subsystems

Description

TheIf Action Subsystemblock is aSubsystemblock preconfigured as a starting point for creating a subsystem whose execution is controlled by anIfblock. TheIfblock evaluates a logical expression and then, depending on the result of the evaluation, outputs an action signal. Execution of the subsystem is controlled by anAction Portblock placed inside the subsystem.

金宝app^®ignores a priority set on anIf Action Subsystemblock. Instead, set the priority on theIfblock that initiates execution of the subsystem.

Merge signals fromIf Action Subsystemblocks

This example shows how to merge signals controlled by anIfblock. TheIfblock selects the execution of anIf Action Subsystemblock from a set of subsystems. Regardless of which subsystem the If block selects, you can create a single signal with aMergeblock. To open the model, seeex_if_block.

All blocks in anIf Action Subsystemblock must execute at the same rate as the drivingIfblock. You can satisfy this requirement by setting the sample time parameter for each block to either inherited (-1) or the same value as theIfblock sample time.

Support for Fixed-Point Data Type

TheIfblock does not directly support fixed-point data types. However, you can use theCompare To Constantblock to work around this limitation.

Consider the following floating-point model without fixed-point data types. To open model, seeex_if_block_floating_point.

In this model, theIf Action Subsystemblocks use their default configurations. The simulation parameters are set to their default values except for the parameters listed in the following table.

Configuration Parameter Pane	Parameter	Setting
Solver	Start time	`0.0`
	停止时间	`1.0`
	Type	`Fixed-step`
	Solver	`discrete (no continuous states)`
	Fixed-step size	`0.1`

The block parameters are set to their default values except for the parameters listed in the following table.

Block	Parameter	Setting
Repeating Sequence Stair	Vector of output values	`[2 1 1 2]”。`
Repeating Sequence Stair1	Vector of output values	`[0 0 0 0 1 1 1 1].'`
If	Number of inputs	`2`
	If expression	`(u1 > 0) \| (u2 > 0.5)`
	Show else condition	Selected
Constant	Constant value	`-4`
Constant1	Constant value	`4`
Scope	Number of axes	`3`
	Time range	`1`

For this model, when inputu1is greater than0or inputu2is greater than0.5, the output is4. Otherwise, the output is-4. TheScopeblock displays the output from theMergeblock with inputsu1, andu2.

You can implement this block diagram as a model with fixed-point data types. To open model, seeex_if_block_fixed_point.

TheRepeating Sequence Stairblocks output fixed-point data types.

TheCompare To Constantblocks implement two parts of theIf expressionthat is used in theIfblock in the floating-point version of the model,(u1 > 0)and(u2 > 0.5). TheORoperation,(u1|u2), can still be implemented inside theIfblock. For a fixed-point model, the expression must be partially implemented outside of theIf块,我s in this model.

The block and simulation parameters for the fixed-point model are the same as for the floating-point model with the following exceptions and additions:

Block	Parameter	Setting
Compare To Constant	Operator	`>`
	Constant value	`0`
	出put data type mode	`Boolean`
	Enable zero-crossing detection	off
Compare To Constant1	Operator	`>`
	Constant value	`0.5`
	出put data type mode	`Boolean`
	Enable zero-crossing detection	off
If	Number of inputs	`2`
	If expression	`u1\|u2`

Ports

Input

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`In`— Signal input to a subsystem block
scalar | vector | matrix

Placing anInportblock in a subsystem block adds an external input port to the block. The port label matches the name of theInportblock.

UseInportblocks to get signals from the local environment.

`Action`— Control signal input to a subsystem block
scalar | vector | matrix

Placing anAction Portblock in a subsystem block adds an external input port to the block and changes the block to anIf Action Subsystem.

Dot-dash lines from aSwitch Caseblock to anSwitch Case Action Subsystemblock representactionsignals. An action signal is a control signal connected to the action port of a Switch Case Action Subsystem block. A message on the action signal initiates execution of the subsystem.

Data Types:action

出put

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`出`— Signal output from a subsystem
scalar | vector | matrix

Placing an出portblock in a subsystem block adds an output port from the block. The port label on the subsystem block is the name of the出portblock.

Use出portblocks to send signals to the local environment.

Model Examples

Simulink Subsystem Semantics

This set of examples shows different types of Simulink® Subsystems and what semantics are used when simulating these Subsystems. Each example provides a description of the model and the subtleties governing how it will be executed.

Open Model

If-Then-Else Blocks

The effect of feeding a sine wave into If Action Subsystem blocks. It is designed to illustrate the similarity between the If Action Subsystem block and the Enabled Subsystem block.

Open Model

Modeling Clutch Lock-Up Using If Blocks

Use If/Else subsystems to build a clutch model. An 'If' subsystem models the clutch dynamics in the locked position while an 'Else' subsystem models the unlocked position. One or the other is enabled using the 'If' block. The dot-dashed lines from the 'If' block denote control signals, which are used to enable If/Else (or other conditional) subsystems. Checking any of the boxes on the GUI produces a plot of any of the selected variables (versus time).

Open Model

Block Characteristics

Data Types	`Boolean^[a]`\|`bus^[a]`\|`double^[a]`\|`enumerated^[a]`\|`fixed point^[a]`\|`一半^[a]`\|`integer^[a]`\|`single^[a]`\|`string^[a]`
Direct Feedthrough	`no`
Multidimensional Signals	`limited^[a]`
Variable-Size Signals	`limited^[a]`
Zero-Crossing Detection	`no`
^[a]Actual data type or capability support depends on block implementation.

Extended Capabilities

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

Actual data type or capability support depends on block implementation.

If Action Subsystem

Description