Simulink®

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

Library

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, Simulink software displays an error when it compiles the model, for example, at the beginning of a simulation. If no conflict exists, Simulink 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 and you use Signal Specification blocks to connect your part of the model with your colleague's. Now, if your colleague changes the attributes of a signal without informing you, the attributes entering the corresponding Signal Specification block do not match and Simulink software reports an appropriate error.

The Signal Specification block can also be used to ensure correct propagation of signal attributes throughout a model. The capability of allowing many attributes to be propagated from block to block in Simulink software is very powerful. However, because blocks may not specify some or all of the attributes of the signals they accept or output, it is possible to create models that don't have enough information to correctly propagate attributes around the model. For these cases, the Signal Specification block is a good way of providing the information Simulink software needs. Using the Signal Specification block also helps speed up model compilation when blocks are missing signal attributes.

Data Type Support

The Signal Specification block accepts real or complex signals of any data type supported by Simulink software, including fixed-point and enumerated data types. The input data type must match the data type specified by the Data type parameter.

For a discussion on the data types supported by Simulink software, see Data Types Supported by Simulink in the Simulink documentation.

Parameters and Dialog Box

Dimensions

Specify the dimension's of the block's input and output signals. Valid values are

• -1 — Inherited from the block to which it is connected

• n — Vector signal of width n

• [m n] — Matrix signal having m rows and n columns

Sample Time

Specify the sample time at which the block is updated. Valid values are

• -1 — Inherited from the block to which it is connected

• period >= 0

• [period, offset]

• [0, -1]

• [-1, -1]

where period is the sample rate and offset is the offset of the sample period from time zero. See Specifying Sample Time in the online documentation for more information.

Minimum

Specify the minimum value that the block should output. The default value, [], is equivalent to -Inf. Simulink software uses this value to perform:

• Simulation range checking (see Checking Signal Ranges)

• Automatic scaling of fixed-point data types

Maximum

Specify the maximum value that the block should output. The default value, [], is equivalent to Inf. Simulink software uses this value to perform:

• Simulation range checking (see Checking Signal Ranges)

• Automatic scaling of fixed-point data types

Data type

Specify the output data type. You can set it to:

• A rule that inherits a data type, for example, Inherit: auto

• The name of a built-in data type, for example, single

• The name of a data type object, for example, a Simulink.NumericType object

• An expression that evaluates to a data type, for example, float('single')

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the Data type parameter.

See Specifying Block Output Data Types for more information.

Lock output scaling against changes by the autoscaling tool

Select to lock scaling of outputs. This parameter is visible only if you enter an expression for the Data type parameter.

Signal type

Specify the numeric type (real or complex) of the input and output signal. To let Simulink software determine the numeric type, set this parameter to auto.

Sampling mode

Specify the sampling mode (sample-based or frame-based) of this block. To let Simulink software determine the sampling mode, set this parameter to auto.

Characteristics

Signal Generator

Sine, Cosine