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Data Store Read

Read data from data store

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  • Data Store Read block

Libraries:
Simulink / Signal Routing

Description

The Data Store Read block copies data from the named data store or a selected portion thereof to its output. More than one Data Store Read block can read from the same data store.

The data store from which the data is read is determined by the location of the Data Store Memory block or signal object that defines the data store. For more information, see Data Stores and Data Store Memory.

Obtaining correct results from data stores requires ensuring that data store reads and writes occur in the expected order. See Order Data Store Access and Data Store Diagnostics for details.

You can select a Data Store Read, Data Store Write, or Data Store Memory block to highlight blocks related to it. To show a related block in an open diagram or new tab, pause on the ellipsis that appears after selection. Then, select Related Blocks from the action bar. When multiple blocks correspond to the selected block, a list of related blocks opens. You can filter the list of related blocks by entering a search term in the text box. After you select a related block from the list, window focus goes to the open diagram or new tab that shows the related block.

Element Selection tab is not supported when the Data Store Read block reads from a Data Store Memory block with the Dimensions parameter value set to Inf. In other words, the Data Store Read block reads unbounded variable-size signals from the data store.

Examples

Share Data Among Multiple Instances of a Reusable Algorithm

Share Data Among Multiple Instances of a Reusable Algorithm

Use a Data Store Memory block to share data among multiple instances of an algorithm in a model.

Initialize, Reset, and Terminate State of Simulink Block

Initialize, Reset, and Terminate State of Simulink Block

Use the Initialize Function, Reset Function, and Terminate Function blocks to respond to events in a Simulink model.

Ports

Input

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External port that specifies an index for the selection of the corresponding data store subelements.

Dependencies

To enable an external index port, on the Element Selection tab, select Enable indexing. Then, in the Nth row of the Index Option table, set Index Option to Index vector (port) or Starting index (port).

Data Types: int8 | int16 | int32 | uint8 | uint16

Output

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Values from the specified data store, provided at the output with the same data type and number of dimensions as in the data store. The block supports both real and complex signals. You can choose whether the block provides the entire data store or only selected elements.

You can use arrays of buses with a Data Store Read block. For details about defining and using an array of buses, see Group Nonvirtual Buses in Arrays of Buses.

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

Parameters

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Parameters

Specify the name of the data store from which this block reads data. The adjacent list provides the names of Data Store Memory blocks that exist at the same level in the model as the Data Store Read block or at higher levels. The list also includes all Simulink.Signal objects in the base and model workspaces. To change the name, select a name from the list or enter the name directly in the edit field.

When compiling a model containing this block, the software searches the model upwards from the level of the block for a Data Store Memory block having the specified data store name. If the software does not find such a block, it searches the model workspace and the MATLAB® workspace for a Simulink.Signal object that has the same name. If the software finds the signal object, it creates a hidden Data Store Memory block at the root level of the model with the properties specified by the Signal object and an initial value set to an array of zeros. The dimensions of that array are inherited from the Dimensions property of the Signal object.

If the software finds neither the Data Store Memory block nor the Signal object, it halts the compilation and issues an error. See Symbol Resolution for more information about the search path.

Programmatic Use

Block Parameter: DataStoreName
Type: string | character vector
Values: data store name
Default: 'A'

This parameter is read-only.

This field lists the Data Store Memory block that initialized the data store from which this block reads.

This parameter is read-only.

This field lists the path to all Data Store Write blocks with the same data store name as this block that are in the same subsystem or in any subsystem below it in the model hierarchy. Click any entry in this list to highlight the corresponding block in your model.

The sample time, which controls when the block reads from the data store. A value of -1 indicates that the sample time is inherited. See Specify Sample Time for more information.

Programmatic Use

Block Parameter: SampleTime
Type: string | character vector
Values: scalar | vector
Default: '-1'

Element Selection

List of elements in the associated data store. For data stores containing arrays, you can read the whole data store, or you can specify one or more elements of the data store. For data stores with a bus data type, you can expand the tree to view and select the bus elements. The list displays the maximum dimensions for each element in parentheses.

If Enable indexing is not selected, select an element and use one of the following approaches:

  • Click Select>> to display that element and all its subelements in the Selected element(s) list.

  • Use the Specify element(s) to select edit box to specify the subelements that you want to select for reading. Then click Select>>.

To select multiple elements, repeat the above procedure for each element.

Alternatively, you can select Enable indexing, then select a single element and specify the subelements dynamically using the Index Option parameter.

To refresh the display and reflect modifications to the array or bus used in the data store, click Refresh.

Dependencies

The prompt for this section (Elements in the array or Signals in the bus) depends on the type of data in the data store.

Programmatic Use

Block Parameter: DataStoreElements
Type: string | character vector
Values: pound-delimited list of elements (See Specification using the command line.)
Default: ''

Enter a MATLAB expression to define a specific element that you want to read, then click Select>> to add the element to the Selected elements(s) table. Repeat to select additional elements.

For example, for a data store named DSM that has maximum dimensions of [3,5], you could enter expressions such as DSM(2,4) or DSM([1 3],2) in the edit box. See Accessing Specific Bus and Matrix Elements.

To apply the element selection, click OK or Apply.

Dependencies

The Specify element(s) to select edit box appears only if Enable indexing is not selected.

Programmatic Use

Block Parameter: DataStoreElements
Type: string | character vector
Values: pound-delimited list of elements (See Specification using the command line.)
Default: ''

Elements that you select from the data store. The Data Store Read block icon displays an output port for each element that you specify.

To change the order of bus or matrix elements in the list, select the element in the list and click Up or Down. Changing the order of the elements in the list changes the order of the ports. To remove an element, click Remove.

Dependencies

The Selected element(s) table appears only if Enable indexing is not selected.

Programmatic Use

Block Parameter: DataStoreElements
Type: string | character vector
Values: pound-delimited list of elements (See Specification using the command line.)
Default: ''

Select this parameter to enable indexing similar to that used by the Selector block, whereby you can dynamically specify indices of subelements to read by using one or more index input ports, as well as specifying indices by using the block dialog. A Data Store Read block can read from only a single element of a data store (that is, a single signal in a bus) when this parameter is selected. To read from multiple elements of a data store using dynamic indexing, use multiple Data Store Read blocks.

Clear this parameter to disable Selector block-style indexing. You can select multiple data store elements to read, but you can specify which subelements to read only by using the block dialog.

Note

Do not select Enable indexing if the associated data store contains only a single, scalar element.

Programmatic Use

Block Parameter: EnableIndexing
Type: string | character vector
Values: "off" | "on"
Default: "off"

Number of dimensions of selected data store element. You must explicitly indicate this number.

Dependencies

This parameter is enabled only if Enable indexing is selected.

Programmatic Use

Block Parameter: NumberOfDimensions
Type: string | character vector
Values: positive integer
Default: '1'

Select the indexing mode. If One-based is selected, an index of 1 specifies the first element of the input vector. If Zero-based is selected, an index of 0 specifies the first element of the input vector.

Dependencies

To enable this parameter, select Enable indexing.

Programmatic Use

Parameter: IndexMode
Type: string | character vector
Values: "Zero-based" | "One-based"
Default: 'One-based'

Define, by dimension, how the subelements of the selected data store element are to be indexed. From the list, select:

Menu ItemAction
Select all

All subelements are read.

Index vector (dialog)

Enables the Index column. Enter a vector containing the indices of subelements to be read.

Index vector (port)

The relevant index port defines the indices of subelements to be read.

Starting index (dialog)

Enables the Index and Output Size columns. Enter the starting index and size of the range of subelements to be read.

Starting index (port)

Enables the Output Size column. The relevant index port defines the starting index of the range of elements to be read. Enter the size of the range.

The Index and Output Size columns are displayed as relevant.

Dependencies

To enable this parameter, select Enable indexing.

Programmatic Use

Parameter: IndexOptionArray
Type: string | character vector
Values: "Select all" | "Index vector (dialog)" | "Index vector (port)" | "Starting index (dialog)" | "Starting index (port)"
Default: 'Index vector (dialog)'

If the Index Option is Index vector (dialog), enter a vector containing the indices of each subelement to read.

If the Index Option is Starting index (dialog), enter the starting index of the range of subelements to read.

Dependencies

To enable this parameter, select Enable indexing and set Index Option for the dimension to Index vector (dialog) or Starting index (dialog).

Programmatic Use

Parameter: IndexParamArray
Type: character vector
Values: cell array
Default: '{ }'

If the Index Option is Starting index (dialog) or Starting index (port), enter the size of the range of subelements to read.

Dependencies

To enable this parameter, select Enable indexing and set Index Option for the dimension to Starting index (dialog) or Starting index (port).

Programmatic Use

Block Parameter: OutputSizeArray
Type: character vector
Values: cell array
Default: '{ }'

Block Characteristics

Data Types

Boolean | bus | double | enumerated | fixed point | half | integer | single | string

Direct Feedthrough

no

Multidimensional Signals

yes

Variable-Size Signals

no

Zero-Crossing Detection

no

Extended Capabilities

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

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

Version History

Introduced before R2006a

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See Also

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