Table Of Contents

Read Tag (G Dataflow)

Last Modified: March 15, 2017

Returns the data value stored in a tag.

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tag ref in

The reference to the tag from which you want to read the data value.

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data type

The data type of the tag you want to read from.

The data type of this input automatically changes to match the data type of the tag you want to read from. If this node cannot determine the data type of the tag at run time, this node may return an error if you do not wire a value to this input.

Default: 0

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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tag ref out

The reference to the tag that this node read the data value from.

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value

The data value stored in the tag.

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timestamp

The timestamp associated with the data value.

This output is available only if you enable the Has Timestamps? property of the tag.

Associating Timestamps with Tag Data

Complete the following steps to associate a timestamp with the data value stored in a tag.

  1. Navigate to the shared resource collection document where you created the tag and select the tag you want to modify.
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    Note  

    Shared resource collection documents have the .grsc file extension.

  2. On the Item tab, enable the Has Timestamps? checkbox.

If the tag contains an initial value, the tag now associates that value with the timestamp when it was created.

You can also associate a custom timestamp to the data value that you write to a tag. If you wire a timestamp to the Write Tag node when writing a new data value to a tag, the node then associates that timestamp with the new data value.

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Note  

Associating a timestamp with tag data may slow down the performance of your application. Only associate timestamps with tag data when necessary.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

What is a Tag?

A tag can store a single value of any data type. Tags are similar to global variables in text-based programming languages. You can create a tag to access the same data from multiple VIs within a project.

Creating and Configuring a Tag

Complete the following steps to create and configure a tag.

  1. Create or open a shared resource collection document.
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    Note  

    Shared resource collection documents have the .grsc file extension.

  2. Expand the Tag section and click Create New.
  3. Configure the data type, initial value, and other properties of the tag in the Item tab.

Where This Node Can Run:

Desktop OS: Windows

FPGA: This product does not support FPGA devices


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