Signal Specification

Specify desired dimensions, sample time, data type, numeric type, and other attributes of signal

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Libraries:
Simulink / Signal Attributes
HDL Coder / Signal Attributes

Description

The Signal Specification block allows you to specify the attributes of the signal connected to its input and output ports. If the specified attributes conflict with the attributes specified by the blocks connected to its ports, the software displays an error when it compiles the model. For example, at the beginning of a simulation, if no conflict exists, the software eliminates the Signal Specification block from the compiled model. In other words, the Signal Specification block is a virtual block. It exists only to specify the attributes of a signal and plays no role in the simulation of the model.

You can use the Signal Specification block to ensure that the actual attributes of a signal meet desired attributes. For example, suppose that you and a colleague are working on different parts of the same model. You use Signal Specification blocks to connect your part of the model with your colleague's. If your colleague changes the attributes of a signal without informing you, the attributes entering the corresponding Signal Specification block do not match. When you try to simulate the model, you get an error.

You can also use the Signal Specification block to ensure correct propagation of signal attributes throughout a model. However, if some blocks have unspecified attributes for the signals they accept or output, the model does not have enough information to propagate attributes correctly. In these cases, the Signal Specification block can provide the information the software needs. Using the Signal Specification block also helps speed up model compilation when blocks are missing signal attributes.

The Signal Specification block supports signal label propagation. For more information, see Signal Label Propagation.

Examples

Modeling Objects with Identical Dynamics Using For Each Subsystem

Model multiple objects with identical dynamics using the For Each subsystem. The number of objects is parameterized by the length of the input signal.

• Open Model

Ports

Input

Port_1 — Input signal

scalar | vector | matrix | N-D array

Input signal whose attributes to check, specified as a scalar, vector, matrix, or N-D array. The block checks the attributes of the input signal against the desired attributes you specify in the block dialog box. If the attributes do not match, the block generates an error.

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 | matrix | N-D array

Output signal is the input signal when all attributes of the signal match those specified in the dialog box. If the attributes do not match, the block generates an error.

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

Parameters

Minimum — Minimum value for range checking

[] (default) | scalar

Specify the minimum value for the block output as a finite real double scalar value.

The software uses this value to perform:

• Simulation range checking (see Specify Signal Ranges)

• Automatic scaling of fixed-point data types

Dependencies

The software ignores the value of this parameter when Data type specifies a Simulink.ValueType or Simulink.Bus object. The software uses the minimum values specified by the Simulink.ValueType object or the Simulink.BusElement objects in the Simulink.Bus object instead.

Programmatic Use

Block Parameter: OutMin

Type: character vector

Values: scalar

Default: '[ ]'

Maximum — Maximum value for range checking

[] (default) | scalar

Specify the maximum value for the block output as a finite real double scalar value.

The software uses this value to perform:

• Simulation range checking (see Specify Signal Ranges)

• Automatic scaling of fixed-point data types

Dependencies

The software ignores the value of this parameter when Data type specifies a Simulink.ValueType or Simulink.Bus object. The software uses the maximum values specified by the Simulink.ValueType object or the Simulink.BusElement objects in the Simulink.Bus object instead.

Programmatic Use

Block Parameter: OutMax

Type: character vector

Values: scalar

Default: '[ ]'

Data type — Output data type

Inherit: auto (default) | double | single | half | int8 | uint8 | int16 | uint16 | ...

Specify the desired output data type. If the data type of the input signal does not match the value you specify, the block generates an error or warning.

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.

You can specify any of these options:

• Inherited data type

• Built-in Simulink^® data type — For example, specify single or uint8. See Data Types Supported by Simulink.

• Fixed-point data type — Use the fixdt function. For example, specify fixdt(1,16,0).

• Enumerated data type — Use the name of the type preceded by Enum:. For example, specify Enum: myEnumType.

• Bus data type — Use the name of the Simulink.Bus object preceded by Bus:. For example, specify Bus: myBusObject.

• Simulink image data type — If you have Computer Vision Toolbox™, use the constructor for the Simulink.ImageType (Computer Vision Toolbox) object and specify the properties to describe the image. By default, the data type uses the Simulink.ImageType(480,640,3) expression that represents the rows, columns, and channels of the image respectively.

• Value type — Use the name of the Simulink.ValueType object preceded by ValueType:. For example, specify ValueType: windVelocity.

• Custom data type — Use a MATLAB^® expression that specifies the type. For example, you can specify a Simulink.NumericType object whose DataTypeMode property is set to a value other than 'Fixed-point: unspecified scaling'.

When you specify a Simulink.ValueType or Simulink.Bus object as the data type, some parameters of the Signal Specification block are ignored. For example, the Min, Max, and Unit parameters of the Signal Specification block are ignored. The software uses the corresponding properties of the Simulink.ValueType object or the Simulink.BusElement objects in the Simulink.Bus object instead. For example, suppose a block sets Unit to ft/s. When the Data type of the block specifies a ValueType object that has m/s as its unit, the block uses m/s instead of ft/s.

Programmatic Use

Block Parameter: OutDataTypeStr

Type: character vector

Value: 'Inherit: auto' | 'double' | 'single' | 'half' | 'int8' | 'uint8' | 'int16' | 'uint16' | 'int32' | 'uint32' | 'int64' | 'uint64' | 'boolean' | 'fixdt(1,16,0)' | 'fixdt(1,16,2^0,0)' | 'string' | 'Enum: <class name>' | 'Bus: <object name>' | 'ValueType: <object name>' | <data type expression> | Simulink.ImageType(480,640,3)

Default: 'Inherit: auto'

Lock output data type setting against changes by the fixed-point tools — Option to prevent fixed-point tools from overriding data types

off (default) | on

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

Dependencies

The software ignores the value of this parameter when Data type specifies a Simulink.ValueType object.

Programmatic Use

Block Parameter: LockScale

Values: 'off' | 'on'

Default: 'off'

Require nonvirtual bus — Accept only nonvirtual bus signals

off (default) | on

If you specify a bus object as the data type, use this parameter to specify whether to accept only nonvirtual bus signals.

• off — Specifies that a signal must come from a virtual bus.

• on — Specifies that a signal must come from a nonvirtual bus.

Dependencies

To enable this parameter, the Data type block parameter must resolve to a Simulink.Bus object.

Programmatic Use

Block Parameter: BusOutputAsStruct

Type: character vector

Value: 'off' | 'on'

Default: 'off'

Unit (e.g., m, m/s^2, N*m) — Physical unit of the input signal to the block

inherit (default) | <Enter unit>

Specify the physical unit of the input signal to the block. To specify a unit, begin typing in the text box. As you type, the parameter displays potential matching units. For a list of supported units, use the showunitslist function.

To constrain the unit system, click the link to the right of the parameter:

• If a Unit System Configuration block exists in the component, its dialog box opens. Use that dialog box to specify allowed and disallowed unit systems for the component.

• If a Unit System Configuration block does not exist in the component, the model Configuration Parameters dialog box displays. Use that dialog box to specify allowed and disallowed unit systems for the model.

Dependencies

The software ignores the value of this parameter when Data type specifies a Simulink.ValueType or Simulink.Bus object. The software uses the units specified by the Simulink.ValueType object or the Simulink.BusElement objects in the Simulink.Bus object instead.

Programmatic Use

Block Parameter: Unit

Type: character vector

Values: 'inherit' | '<Enter unit>'

Default: 'inherit'

To specify the physical unit of the input signal to the block without propagation, use UnitNoProp.

Dimensions (-1 for inherited) — Dimensions of input and output signals

-1 (default) | n | [m n]

Specify the dimensions of the input and output signals.

• -1 — Specifies that signals inherit dimensions.

• n — Specifies a vector of width n.

• [m n] — Specifies a matrix with m rows and n columns.

Dependencies

The software ignores the value of this parameter when Data type specifies a Simulink.ValueType object. The software uses the dimensions specified by the Simulink.ValueType object instead.

Programmatic Use

Block Parameter: Dimensions

Type: character vector

Values: '-1' | n | [m n]

Default: '-1'

Variable-size signal — Allow signal to be variable-size, fixed-size, or both

Inherit (default) | No | Yes

Specify the signal to be of variable-size, fixed size, or both.

• Inherit — Allows variable-size and fixed-size signals.

• No — Does not allow variable-size signals.

• Yes — Allows only variable-size signals.

When the signal is a variable-size signal, the Dimensions parameter specifies the maximum dimensions of the signal.

Dependencies

• When Data type specifies a Simulink.Bus object, the simulation allows variable-size signals only with a disabled bus object.

• The software ignores the value of this parameter when Data type specifies a Simulink.ValueType object. The software uses the dimensions mode specified by the Simulink.ValueType object instead.

Programmatic Use

Block Parameter: VarSizeSig

Type: character vector

Values: 'Inherit' | 'No' | 'Yes'

Default: 'Inherit'

Sample time (-1 for inherited) — Time interval between samples

-1 (default) | scalar | vector

Specify the time interval between samples. To inherit the sample time, set this parameter to -1. See Specify Sample Time for more information.

Programmatic Use

Parameter: SampleTime

Type: character vector

Values: Any valid sample time

Default: '-1'

Signal type — Complexity of signal

auto (default) | real | complex

Specify the complexity of the input and output signals.

• auto — Accepts either real or complex as the numeric type.

• real — Specifies the numeric type as a real number.

• complex — Specifies the numeric type as a complex number.

Dependencies

The software ignores the value of this parameter when Data type specifies a Simulink.ValueType or Simulink.Bus object. The software uses the complexity specified by the Simulink.ValueType object or the Simulink.BusElement objects in the Simulink.Bus object instead.

Programmatic Use

Parameter: SignalType

Type: character vector

Values: 'auto' | 'real' | 'complex'

Default: 'auto'

Mode — Data type mode

Inherit (default) | Built in | Fixed point | Enumerated | Bus object | Value type | Expression

Select the category of data to specify. For more information, see Specify Data Types Using Data Type Assistant.

Inherit

Inheritance rules for data types. Selecting Inherit enables auto.

Built in

Built-in data types. Selecting Built in enables a list of possible values:

• double (default)

• single

• int8

• uint8

• int16

• uint16

• int32

• uint32

• int64

• uint64

• boolean

Fixed point

Fixed-point data types.

Enumerated

Enumerated data types. Selecting Enumerated enables a text box to the right, where you can enter a class name.

Bus object

Bus object. Selecting Bus object enables a text box to the right, where you enter the name of a bus object that you want to use to define the structure of the bus. To create or change a bus object, click Edit to the right of the text box.

Value type

Value type. Selecting Value type enables a text box to the right, where you enter the name of a value type that you want to use to define the properties of the signal. To create or change a value type, click Edit to the right of the text box.

Expression

Expressions that evaluate to data types. Selecting Expression enables a text box to the right, where you can enter the expression.

Do not specify a bus object as the expression.

Dependencies

To enable this parameter, click the Show data type assistant button .

Signedness — Signed or unsigned

Signed

Specify whether the fixed-point data is signed or unsigned. Signed data can represent positive and negative values, but unsigned data represents positive values only.

• Signed, specifies the fixed-point data as signed.

• Unsigned, specifies the fixed-point data as unsigned.

For more information, see Specify Data Types Using Data Type Assistant.

Dependencies

To enable this parameter, set Mode to Fixed point.

Data type override — Specify data type override mode for this signal

Inherit | Off

Select the data type override mode for this signal.

• When you select Inherit, Simulink inherits the data type override setting from its context, that is, from the block, Simulink.Signal object or Stateflow^® chart in Simulink that is using the signal.

• When you select Off, Simulink ignores the data type override setting of its context and uses the fixed-point data type specified for the signal.

For more information, see Specify Data Types Using Data Type Assistant in the Simulink documentation.

Dependencies

To enable this parameter, set Mode to Built in or Fixed point.

Tips

The ability to turn off data type override for an individual data type provides greater control over the data types in your model when you apply data type override. For example, you can use this option to ensure that data types meet the requirements of downstream blocks regardless of the data type override setting.

Word length — Bit size of the word that holds the quantized integer

16 (default) | integer from 0 to 32

Specify the bit size of the word that holds the quantized integer. For more information, see Specifying a Fixed-Point Data Type.

Dependencies

To enable this parameter, set Mode to Fixed point.

Scaling — Method for scaling fixed-point data

Best precision (default) | Binary point | Slope and bias

Specify the method for scaling your fixed-point data to avoid overflow conditions and minimize quantization errors. For more information, see Specifying a Fixed-Point Data Type.

Dependencies

To enable this parameter, set Mode to Fixed point.

Fraction length — Specify fraction length for fixed-point data type

0 (default) | scalar integer

Specify fraction length for fixed-point data type as a positive or negative integer. For more information, see Specifying a Fixed-Point Data Type.

Dependencies

To enable this parameter, set Scaling to Binary point.

Slope — Specify slope for the fixed-point data type

2^0 (default) | positive, real-valued scalar

Specify slope for the fixed-point data type. For more information, see Specifying a Fixed-Point Data Type.

Dependencies

To enable this parameter, set Scaling to Slope and bias.

Bias — Specify bias for the fixed-point data type

0 (default) | real-valued scalar

Specify bias for the fixed-point data type as any real number. For more information, see Specifying a Fixed-Point Data Type.

Dependencies

To enable this parameter, set Scaling to Slope and bias.

Block Characteristics

Data Types	Boolean | bus | double | enumerated | fixed point | half | integer | single | string
Direct Feedthrough	no
Multidimensional Signals	yes
Variable-Size Signals	yes
Zero-Crossing Detection	no

Extended Capabilities

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

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 a pass-through implementation.

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.

Simulink.ValueType Object Support

This block supports code generation for Simulink.ValueType object. For more information about value types, see Specify Common Set of Signal Properties as Value Type.

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

Version History

Introduced before R2006a