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Write Tag (Clock-Driven Logic)

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Last Modified: June 25, 2019

Writes a data value to a tag, or to a tag proxy if it is configured to have write access.

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tag/proxy ref in

The reference to the tag endpoint, or tag proxy endpoint if configured to have write access, to which to write a data value.

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value

The data value that this node writes to the tag or tag proxy.

Data Type of value

tag/proxy ref in
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timestamp

The timestamp you want to associate with the data value that this node writes to the tag.

This input is available only if all of the following conditions are met:

  • When you create the tag, you enable the Has Timestamps? property.
  • You wire a reference to that tag to tag ref in.

If you do not wire this input and Has Timestamps? is enabled, this node automatically generates the current timestamp and associates it with the data value in 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 the tag 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 the performance of your application. Associate timestamps with tag data only when necessary.

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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/proxy ref out

The reference to the tag endpoint or tag proxy endpoint to which this node wrote a data value.

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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 is single-point, latest value data that you can access from multiple documents within a project. A tag can store a single value of any data type that represents the state of a process. Tags are similar to global variables in text-based programming languages.

You can create a tag either dynamically, using the Configure and Create Tag node on the diagram, or statically, in the shared resource collection file.

You can create a tag to access the same data from multiple VIs within a project.

What Is a Tag Proxy?

A tag proxy is a reference that is local to part of the application that mirrors the value of the actual tag to which it is linked in another location in the application. You use a tag proxy to access data that is in another location in the application. You can read from and optionally write to a tag proxy only after the tag proxy links to a tag.

Using a Tag Constant

Complete the following steps to statically 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: none

FPGA: All devices

Web Server: Not supported in VIs that run in a web application

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