siemens/tia-portal-ai-extensions/tags-and-tagtables

Tags and TagTables

Overview

Tags and TagTables provide the mechanism for defining and managing PLC variables in TIA Portal. A PlcSoftware contains a TagTableGroup which organizes PlcTagTable instances (e.g., default tag tables, HW tags). Each tag table holds a collection of PlcTag objects that represent individual variables accessible from blocks. Tags can be accessed by name, edited in-place, exported to XML for bulk modification, and re-imported.

Required Namespaces

using Siemens.Engineering;
using Siemens.Engineering.SW;
using Siemens.Engineering.SW.Tags;

Required Assemblies

• Siemens.Engineering.Base.dll
• Siemens.Engineering.Step7.dll

Common Patterns

Access TagTable and PlcTag from PlcSoftware

Description: Navigate from PlcSoftware to its tag tables and individual tags. The TagTableGroup exposes all tag tables associated with the PLC software. Tags are accessed via the Tags property of a specific tag table.

Example:

var myTagTable = plcSoftware.TagTableGroup.TagTables.FirstOrDefault(x => x.Name == "DemocaseAppTagTable");
var myTag = myTagTable.Tags.FirstOrDefault();

Key Types and Methods:

• PlcSoftware.TagTableGroup — the root container for all tag tables
• TagTableCollection — enumerable collection of tag tables
• PlcTagTable.Tags — collection of tags within a tag table

Edit Tag Name In-Place

Description: Modify the name of an existing PlcTag directly by setting its Name property. This is an in-place mutation on the engineering object.

Example:

if (myTag != null)
{
    myTag.Name = "NewTagName2";
}

Key Types and Methods:

• PlcTag.Name — settable property for the tag's symbolic name

Export TagTable to XML and Re-Import

Description: Export an entire tag table to XML, modify the XML using standard .NET XML APIs (e.g., XDocument), then re-import the modified XML back into the project. Useful for bulk tag transformations or migration scenarios.

Example:

myTagTable.Export(new FileInfo(tempPath), ExportOptions.WithDefaults);
// ... modify XML with XDocument ...
plcSoftware.TagTableGroup.TagTables.Import(new FileInfo(tempPath), ImportOptions.Override);

Key Types and Methods:

• PlcTagTable.Export(FileInfo, ExportOptions) — writes tag table to XML file
• TagTableCollection.Import(FileInfo, ImportOptions) — imports tag table from XML file

Find Tag by Name via Collection.Find

Description: Use the Find(string) method on a PlcTagCollection to locate a specific tag by its name. This is more efficient than iterating manually and handles name lookup internally.

Example:

var connectedTag = plcSoftware.TagTableGroup.TagTables
    .First(x => x.Name.ToLower().Contains("default")).Tags.Find("test");

Key Types and Methods:

• PlcTagCollection.Find(string) — returns the tag with the specified name or null

Create Tag Tables and Tags Idempotently

var table = group.TagTables.Find(tableName) ?? group.TagTables.Create(tableName);
table.Tags.Find("Speed")?.Delete();               // idempotent regeneration
var tag = table.Tags.Create("Speed", "Int", "%MW100");

Key points:

• PlcTagComposition.Create(name, dataTypeName, logicalAddress). The address format is %<area><byte>[.<bit>], for example %I187.0, %Q10.0, %MW100, %M50.3.
• Tag names are unique per PLC across all tag tables. Tags.Create throws "An attempt was made to create an object that already exists" on a clash in any table, so include the table name in diagnostics.
• To find a table anywhere below a PlcTagTableGroup, recurse through group.Groups. Search one scope only (PLC root or a SW-Unit's tag-table group), because SW-Units have isolated groups (see `sw-units`).
• Not every tag attribute applies to every tag. Wrap optional per-attribute SetAttribute calls in try/catch, log the failure and continue, rather than aborting a whole table.

Create and Manage User Constants

Description: User constants are named values stored in tag tables, usable in PLC code and array bounds. Use Find before Create to avoid duplicates.

Example:

// Find existing constant
var constant = table.UserConstants.Find("MAX_AXES");
 
// Create if not found
if (constant == null)
    constant = table.UserConstants.Create("MAX_AXES", "Int", "10");
 
// Update value of an existing constant
constant.Value = "12";

Key Types and Methods:

• PlcTagTable.UserConstants — collection of user constants in the tag table
• UserConstants.Find(name) — returns null if not found
• UserConstants.Create(name, dataType, value) — creates and returns the new constant
• PlcUserConstant.Value — settable property for the constant's current value

User constants are referenced in array bounds and PLC code as "CONST_NAME" (with quotes).

Quick Reference

Related Files

• `blocks` — blocks reference tags through their interface members
• `devices-and-hardware` — hardware tags are auto-generated from device configuration

Exception Handling

• EngineeringException may be thrown when exporting/importing tag tables if the file path is invalid or the XML is malformed
• Null checks should be performed after Find() calls since they return null when the tag is not found