Beckhoff TwinCAT Nodes

Read and write Beckhoff TwinCAT 2/3 PLCs directly from pipelines over the ADS protocol. Each function type authored on a TwinCAT connection is available as a matching node in the Pipeline Designer.

For connection setup, AMS routing, the symbolic addressing model, data types, and per-function configuration fields, see the Beckhoff TwinCAT connection guide.

For the event-driven trigger (ADS device notifications), see the TwinCAT Trigger node.

Configuration Quick Reference

Field	What you choose	Details
Parameters	Connection, Function, Function Parameters, Timeout Override	Select the TwinCAT connection profile, pick a function, bind parameters with expression support, and optionally override the timeout.
Settings	Description, Timeout (seconds), Retry on Timeout, Retry on Fail, On Error	Node description, maximum execution time, retry behaviour on timeout or failure, and error strategy. All execution settings default to pipeline-level values.

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TwinCAT Read Nodes

Read PLC variables by symbol path. There are three read node types, one per read function:

Supported Function Types:

Node	Function	Purpose	Common Use Cases
TwinCAT Read Symbol	twincat.read.symbol	Read one typed value by symbol path (or a 1-D scalar array as a list)	Setpoint readback, status/alarm flag, single process value
TwinCAT Read Block	twincat.read.block	Read many named symbols in one ADS sum-up request	Dashboard snapshots, historian logging, mixed-type process blocks
TwinCAT Read Struct	twincat.read.struct	Read a whole struct, decoded field-by-field into a nested object	Machine-status structs, recipe structs

Node Configuration

Parameter	Type	Required	Description
Connection	Selection	Yes	TwinCAT connection profile to use
Function	Selection	Yes	A read function of the matching type from the selected connection
Function Parameters	Dynamic	Varies	Auto-populated from the function schema (symbol/dataType for Read Symbol and Read Struct, or the dataPoints array for Read Block). See the TwinCAT connection functions for field-level details.
Timeout Override	Number (seconds)	No	Override the default function timeout

All function parameters support expression syntax ({{ expression }}) for dynamic values from the pipeline context, and ((paramName)) template placeholders where the function defines them.

Input

The node receives the output of the previous node as input. Input data can be referenced in function parameter expressions using $input.

Output Structure

Read Symbol — a single decoded value:

{
  "result": {
    "symbol": "MAIN.fbMotor.Speed",
    "dataType": "LREAL",
    "value": 72.5
  },
  "_metadata": { "success": true, "functionId": "<function-id>", "durationMs": 9, "timestamp": "2026-06-05T08:30:00Z" }
}

Field	Type	Description
result.symbol	string	Echoes the resolved symbol path (a raw path, or the path a tag alias resolved to)
result.dataType	string	Data type used to decode the value
result.value	any	The decoded value — BOOL → boolean, integer types → number, REAL/LREAL → number, STRING/WSTRING → string, a 1-D scalar array → list

Read Block — a map of decoded values keyed by datapoint name:

{
  "result": {
    "values": {
      "speed": 72.5,
      "running": true,
      "count": 100000,
      "estop": false
    }
  },
  "_metadata": { "success": true, "functionId": "<function-id>", "durationMs": 12, "timestamp": "2026-06-05T08:30:00Z" }
}

Field	Type	Description
result.values	object	Map keyed by datapoint name — every point that decoded successfully appears here.
result.errors	object	(present only if some points failed) Map keyed by datapoint name → error message. Successful points still appear under values.

Read Struct — a nested object keyed by member name:

{
  "result": {
    "symbol": "MAIN.stStatus",
    "dataType": "ST_Status",
    "value": {
      "running": true,
      "speed": 72.5,
      "mode": 2,
      "fault": { "code": 0, "active": false }
    }
  },
  "_metadata": { "success": true, "functionId": "<function-id>", "durationMs": 14, "timestamp": "2026-06-05T08:30:00Z" }
}

Access pattern in downstream nodes:

{{ $node["TwinCAT Read Symbol"].result.value }}
{{ $node["TwinCAT Read Block"].result.values.speed }}
{{ $node["TwinCAT Read Struct"].result.value.fault.code }}

Sum-up batching

A Read Block reads all of its data points in a single ADS sum-up request, regardless of how many points it carries — one round-trip instead of one per tag. A point that fails to resolve or decode is reported under result.errors and does not fail the rest of the batch.

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TwinCAT Write Nodes

Write PLC variables by symbol path. There are two write node types:

Supported Function Types:

Node	Function	Purpose	Common Use Cases
TwinCAT Write Symbol	twincat.write.symbol	Write one typed value to a writable variable	Setpoints, command/start flags, mode changes
TwinCAT Write Struct	twincat.write.struct	Write selected struct members in one atomic write, with optional field-merge	Recipe/config updates, partial struct download

Node Configuration

Parameter	Type	Required	Description
Connection	Selection	Yes	TwinCAT connection profile to use
Function	Selection	Yes	A twincat.write.symbol or twincat.write.struct function from the selected connection
Function Parameters	Dynamic	Varies	Auto-populated from the function schema (symbol, value, dataType for Write Symbol; symbol, fields, autoFill for Write Struct). The value and fields parameters support ((paramName)) templates — see the TwinCAT connection functions.
Timeout Override	Number (seconds)	No	Override the default function timeout

All function parameters support expression syntax ({{ expression }}) and template placeholders (((paramName))). Use expressions like {{ $input[0].result.value }} (an upstream Read Symbol) to feed dynamic values into the value parameter.

Input

The node receives the output of the previous node as input.

Output Structure

Write Symbol — on success:

{
  "result": {
    "symbol": "MAIN.fSetpoint",
    "dataType": "LREAL",
    "value": "42.5"
  },
  "_metadata": { "success": true, "functionId": "<function-id>", "durationMs": 11, "timestamp": "2026-06-05T08:30:00Z" }
}

Field	Type	Description
result.symbol	string	The resolved symbol path that was written
result.dataType	string	Data type used to encode the value
result.value	any	Echo of the value that was written (after parameter substitution)

Write Struct — on success:

{
  "result": {
    "symbol": "MAIN.stConfig",
    "written": ["setpoint", "enabled", "mode"],
    "autoFill": true
  },
  "_metadata": { "success": true, "functionId": "<function-id>", "durationMs": 16, "timestamp": "2026-06-05T08:30:00Z" }
}

Field	Type	Description
result.symbol	string	The struct that was written
result.written	array	The struct members that were written
result.autoFill	boolean	Whether unspecified members were preserved (true) or zeroed (false)

A write to a read-only variable, or a Write Symbol against a struct, returns success: false with a descriptive error and the value is not changed on the PLC.

Safety First

Always validate values in a Condition node before writing to industrial equipment. A setpoint or command flag can move a motor, valve, or actuator immediately. With Write Struct, remember that autoFill = false zeroes every member you didn't list — keep it on (the default) unless you intend to reset the whole struct.

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Settings Tab

All TwinCAT node types share the same Settings tab:

Setting	Type	Default	Description
Description	Text	—	Optional description displayed on the node
Timeout (seconds)	Number	Pipeline default	Maximum time the node may run before timing out
Retry on Timeout	Toggle	Pipeline default	Automatically retry the node if it times out
Retry on Fail	Toggle	Pipeline default	Automatically retry the node if it fails
On Error	Selection	Pipeline default	Error strategy: Pipeline Default (the pipeline's Error Handling setting), Stop Pipeline or Continue Execution

When left at their defaults, these settings inherit from the pipeline-level execution configuration.

Test before wiring

Use the Test Function button in the function form (on the connection page) to validate every TwinCAT read/write/struct function against the live PLC before wiring it into a pipeline. It is the fastest way to catch a wrong symbol path, wrong data type, or a read-only target — and the Symbol Browser confirms exact paths and types.