ADS Connector (Beckhoff)

ADS Overview

The ADS connector enables communication with Beckhoff TwinCAT PLCs and systems using the ADS (Automation Device Specification) protocol. It supports automatic symbol discovery, bidirectional communication, and complex data types including arrays and structures.

ADS provides direct, high-performance access to TwinCAT variables. The AutoDiscovery feature can automatically find and expose all PLC symbols as MQTT topics.

The ADS connector is on beta testing. It is planned for a future release.

Basic Syntax

DEFINE CONNECTOR BeckhoffPLC WITH TYPE ADS
    ADD ADS_CONFIG
        WITH TARGET_NET_ID "192.168.1.100.1.1"
        WITH TARGET_IP "192.168.1.100"
        WITH TARGET_PORT 851
    ADD MAPPING ProcessData
        WITH EVERY 500 MILLISECONDS
        ADD TAG Temperature
            WITH ADDRESS "GVL_Process.rTemperature"
            WITH DATA_TYPE "REAL"
            WITH SOURCE_TOPIC "plc/temperature"

Set the PLC’s AMS Net ID, IP, and ADS port in ADS_CONFIG. The broker connects through the AMS router on the broker host, so create that route on the router or the PLC. See AMS route setup.

AMS Net ID Basics

ADS uses an AMS Net ID for the broker host and one for the PLC. Set the broker host’s id on the AMS router. An AMS Net ID is typically the IP address followed by .1.1.

Component	Format	Example
AMS Net ID	`x.x.x.x.y.y`	`192.168.1.100.1.1`
IP portion	First 4 octets	`192.168.1.100`
Node portion	Last 2 octets	`.1.1` (usually)

You can find your TwinCAT system’s AMS Net ID in TwinCAT XAE under SYSTEM → Connectors or by running adsInfo on the target.

Connection Configuration

ADS_CONFIG Parameters

string

Not required. Accepted and not used yet.

string

Not required. Accepted and not used yet.

string

Local host name (optional).

string

required

Target PLC’s AMS Net ID (format: x.x.x.x.x.x).

string

required

Target PLC’s IP address.

integer

ADS port. Typically 851 for TwinCAT 3, 801 for TwinCAT 2.

string

Not required. Accepted and not used yet.

string

Not required. Accepted and not used yet.

string

Not required. Accepted and not used yet.

The broker connects through the AMS router on the broker host. Create the AMS route on the router or the PLC yourself. LOCAL_NET_ID, LOCAL_ROUTE_TO_TARGET, TARGET_ROUTE_TO_LOCAL, TARGET_USER, and TARGET_PASSWORD do not create that route.

integer

Limit for each ADS request, in milliseconds. Default: 5000. A value of 0 or below falls back to 5000.

A SYMBOL read is 1 request by name. A SYMBOL write takes 3 round trips (create handle, write, release handle), so it can take up to 3 × TIMEOUT plus a margin of at least 1 s. INDEX reads and writes are 1 request. When an ADS error means the PLC is unreachable, such as a timeout or target not found, the route goes to Reconnecting instead of staying Connected with BAD tags. See Connection status.

Connection Example

ADD ADS_CONFIG
    WITH TARGET_NET_ID "192.168.1.100.1.1"
    WITH TARGET_IP "192.168.1.100"
    WITH TARGET_PORT 851
    WITH TIMEOUT 5000

AutoDiscovery

AutoDiscovery automatically finds all PLC symbols and exposes them as MQTT topics.

AutoDiscovery Parameters

boolean

Enable automatic symbol discovery. Default: false.

string

Base MQTT topic for discovered symbols. Default: ads/discovery.

integer

Default QoS for discovered symbols (0-2). Default: 0.

boolean

Default retain flag for discovered symbols. Default: false.

integer

Default trigger mode:

0 - OnStart (read once at connection)
1 - OnChange (publish on value change)
2 - Cyclic (poll at interval)

Default: 2.

integer

Default polling cycle in milliseconds. Default: 1000.

string

Include patterns (comma-separated, * wildcard). Default: * (all symbols).

string

Exclude patterns (comma-separated, * wildcard).

integer

Structure expansion depth. Default: 3.

boolean

Enable parallel reading for large projects. Default: false.

integer

Batch size for parallel reading. Default: 50.

AutoDiscovery Example

DEFINE CONNECTOR BeckhoffAutoDiscover WITH TYPE ADS
    ADD ADS_CONFIG
        WITH TARGET_NET_ID "192.168.1.100.1.1"
        WITH TARGET_IP "192.168.1.100"
        WITH TARGET_PORT 851
        WITH AUTO_DISCOVERY "true"
        WITH DISCOVERY_BASE_TOPIC "beckhoff/plc"
        WITH DISCOVERY_FILTER_INCLUDES "GVL_*"
        WITH DISCOVERY_FILTER_EXCLUDES "*_Internal*"
        WITH DISCOVERY_DEFAULT_CYCLE 500
        WITH DISCOVERY_MAX_DEPTH 3

TwinCAT Data Types

Data Type	TwinCAT Type	Size	Description
`BOOL`	BOOL	1 bit	Boolean value
`BYTE`	BYTE	8 bits	Unsigned 8-bit
`SINT`	SINT	8 bits	Signed 8-bit integer
`USINT`	USINT	8 bits	Unsigned 8-bit integer
`WORD`	WORD	16 bits	Unsigned 16-bit
`INT`	INT	16 bits	Signed 16-bit integer
`UINT`	UINT	16 bits	Unsigned 16-bit integer
`DWORD`	DWORD	32 bits	Unsigned 32-bit
`DINT`	DINT	32 bits	Signed 32-bit integer
`UDINT`	UDINT	32 bits	Unsigned 32-bit integer
`LWORD`	LWORD	64 bits	Unsigned 64-bit
`LINT`	LINT	64 bits	Signed 64-bit integer
`ULINT`	ULINT	64 bits	Unsigned 64-bit integer
`REAL` / `FLOAT`	REAL	32 bits	32-bit floating point
`LREAL` / `DOUBLE`	LREAL	64 bits	64-bit floating point
`CHAR`	CHAR	8 bits	Single character
`WCHAR`	WCHAR	16 bits	Wide character
`TIME`	TIME	32 bits	Time duration
`DATE`	DATE	16 bits	Date value
`TOD`	TOD	32 bits	Time of day
`STRING`	STRING	Variable	ASCII string; sized with `LENGTH`
`ARRAY`	ARRAY	Variable	Array of elements (requires `ARRAY_ELEMENT_TYPE`)
`STRUCT`	STRUCT	Variable	Structured data type

String sizing

For STRING tags, WITH LENGTH is the total size in bytes, including the ADS length byte. It defaults to 256 bytes for reads; writes use an 80-byte default when no size is supplied. STRING_SIZE is accepted as an alias for the same field. ARRAY_ELEMENT_LENGTH is a separate setting for ARRAY tags whose elements are STRING or STRUCT — it does not replace LENGTH on scalar string tags. Read a TwinCAT STRING symbol with an explicit read size (256 bytes here; writes default to 80 bytes when LENGTH is omitted):

DEFINE CONNECTOR TwinCATStrings WITH TYPE ADS
    ADD ADS_CONFIG
        WITH TARGET_NET_ID "192.168.1.100.1.1"
        WITH TARGET_IP "192.168.1.100"
        WITH TARGET_PORT 851
    ADD MAPPING Labels
        WITH EVERY 1 SECOND
        ADD TAG ProductLabel
            WITH ADDRESS "GVL_Process.sProductName"
            WITH ADDRESS_TYPE "SYMBOL"
            WITH DATA_TYPE "STRING"
            WITH LENGTH 256
            WITH SOURCE_TOPIC "production/label"

TAG Configuration

Symbol-Based Addressing

ADD TAG Temperature
    WITH ADDRESS "GVL_Process.rTemperature"
    WITH ADDRESS_TYPE "SYMBOL"
    WITH DATA_TYPE "REAL"
    WITH SOURCE_TOPIC "plc/temperature"

Index-Based Addressing

For direct memory access using index group and offset:

ADD TAG DirectValue
    WITH ADDRESS "16448.0"
    WITH ADDRESS_TYPE "INDEX"
    WITH DATA_TYPE "DINT"
    WITH SOURCE_TOPIC "plc/direct"

Array Handling

string

Array element type (required for ARRAY): BOOL, INT, REAL, STRING, STRUCT, etc.

integer

Number of elements in the array.

integer

Length of each element in bytes (for STRING/STRUCT arrays).

integer

Offset in bytes to skip before array data. Default: 0.

integer

Header bytes to skip per element. Default: 0.

Structure Handling

string

Structure field definitions in format: name:offset:type:size (comma-separated).

String sizing parameter

integer

Total string size in bytes, including the ADS length byte. Default: 256 for reads; 80 for writes when omitted. Alias: STRING_SIZE.

Event-Based Operations

For on-demand ADS operations (not polling), use the EVENT syntax. Publish a message to SOURCE_TOPIC to trigger the operation; the connector executes it and publishes the result to DESTINATION_TOPIC.

Supported Operations

Operation	Description	Query Parameters
`READ`	Read a symbol value on demand	`symbol`, `data_type`
`WRITE`	Write a value to a symbol	`symbol`, `data_type`, `value`

Query Parameters

Parameter	Description	Example
`operation`	Operation type: `READ` or `WRITE`	`READ`
`symbol`	TwinCAT symbol path	`GVL_Process.rTemperature`, `GVL_Control.rSP`
`data_type`	TwinCAT data type	`REAL`, `LREAL`, `DINT`, `BOOL`, `INT`
`value`	Value to write (WRITE only)	`75.0`, `42`, `true`

Read Example

Read a process variable on demand:

ADD EVENT ReadSymbol
    WITH SOURCE_TOPIC "ads/commands/read"
    WITH DESTINATION_TOPIC "ads/responses/read"
    WITH QUERY "{operation: READ, symbol: GVL_Process.rTemperature, data_type: REAL}"

Write Example

Write a setpoint on demand:

ADD EVENT WriteSetpoint
    WITH SOURCE_TOPIC "ads/commands/write"
    WITH DESTINATION_TOPIC "ads/responses/write"
    WITH QUERY "{operation: WRITE, symbol: GVL_Control.rSP, data_type: REAL, value: 75.0}"

Complete Examples

Read PLC variables using symbol names:

DEFINE CONNECTOR TwinCATBasic WITH TYPE ADS
    ADD ADS_CONFIG
        WITH TARGET_NET_ID "192.168.1.100.1.1"
        WITH TARGET_IP "192.168.1.100"
        WITH TARGET_PORT 851
    ADD MAPPING ProcessVariables
        WITH EVERY 500 MILLISECONDS
        ADD TAG Temperature
            WITH ADDRESS "GVL_Process.rTemperature"
            WITH ADDRESS_TYPE "SYMBOL"
            WITH DATA_TYPE "REAL"
            WITH SOURCE_TOPIC "plc/process/temperature"
            WITH UNIT "°C"
        ADD TAG Pressure
            WITH ADDRESS "GVL_Process.rPressure"
            WITH ADDRESS_TYPE "SYMBOL"
            WITH DATA_TYPE "REAL"
            WITH SOURCE_TOPIC "plc/process/pressure"
            WITH UNIT "bar"
        ADD TAG RunningState
            WITH ADDRESS "GVL_Process.bRunning"
            WITH ADDRESS_TYPE "SYMBOL"
            WITH DATA_TYPE "BOOL"
            WITH SOURCE_TOPIC "plc/process/running"

Automatically discover and expose all GVL variables:

DEFINE CONNECTOR TwinCATAutoDiscover WITH TYPE ADS
    ADD ADS_CONFIG
        WITH TARGET_NET_ID "192.168.1.100.1.1"
        WITH TARGET_IP "192.168.1.100"
        WITH TARGET_PORT 851
        WITH AUTO_DISCOVERY "true"
        WITH DISCOVERY_BASE_TOPIC "twincat"
        WITH DISCOVERY_FILTER_INCLUDES "GVL_Production.*,GVL_Process.*"
        WITH DISCOVERY_FILTER_EXCLUDES "*_Debug*,*_Test*"
        WITH DISCOVERY_DEFAULT_CYCLE 500
        WITH DISCOVERY_MAX_DEPTH 2
        WITH DISCOVERY_PARALLEL_READING "true"
        WITH DISCOVERY_BATCH_SIZE 100

Read process values and write setpoints:

DEFINE CONNECTOR TwinCATControl WITH TYPE ADS
    ADD ADS_CONFIG
        WITH TARGET_NET_ID "192.168.1.100.1.1"
        WITH TARGET_IP "192.168.1.100"
        WITH TARGET_PORT 851
    ADD MAPPING ControlLoop
        WITH EVERY 200 MILLISECONDS
        ADD TAG ProcessValue
            WITH ADDRESS "GVL_Control.rPV"
            WITH DATA_TYPE "REAL"
            WITH SOURCE_TOPIC "control/pv"
            WITH UNIT "°C"
        ADD TAG Setpoint
            WITH ADDRESS "GVL_Control.rSP"
            WITH DATA_TYPE "REAL"
            WITH SOURCE_TOPIC "control/sp"
            WITH WRITABLE "true"
            WITH DESTINATION_TOPIC "control/sp/write"
            WITH MIN_VALUE 0
            WITH MAX_VALUE 100
        ADD TAG Output
            WITH ADDRESS "GVL_Control.rOutput"
            WITH DATA_TYPE "REAL"
            WITH SOURCE_TOPIC "control/output"
            WITH UNIT "%"
        ADD TAG AutoMode
            WITH ADDRESS "GVL_Control.bAutoMode"
            WITH DATA_TYPE "BOOL"
            WITH SOURCE_TOPIC "control/auto"
            WITH WRITABLE "true"
            WITH DESTINATION_TOPIC "control/auto/write"

Read array values:

DEFINE CONNECTOR TwinCATArrays WITH TYPE ADS
    ADD ADS_CONFIG
        WITH TARGET_NET_ID "192.168.1.100.1.1"
        WITH TARGET_IP "192.168.1.100"
        WITH TARGET_PORT 851
    ADD MAPPING ArrayData
        WITH EVERY 1 SECOND
        ADD TAG TemperatureArray
            WITH ADDRESS "GVL_Data.arTemperatures"
            WITH DATA_TYPE "ARRAY"
            WITH ARRAY_ELEMENT_TYPE "REAL"
            WITH ARRAY_SIZE 10
            WITH SOURCE_TOPIC "plc/temperatures"
            WITH PUBLISH_MODE "JSON"
        ADD TAG StatusBits
            WITH ADDRESS "GVL_Data.arStatus"
            WITH DATA_TYPE "ARRAY"
            WITH ARRAY_ELEMENT_TYPE "BOOL"
            WITH ARRAY_SIZE 16
            WITH SOURCE_TOPIC "plc/status"

Read structured data:

DEFINE CONNECTOR TwinCATStruct WITH TYPE ADS
    ADD ADS_CONFIG
        WITH TARGET_NET_ID "192.168.1.100.1.1"
        WITH TARGET_IP "192.168.1.100"
        WITH TARGET_PORT 851
    ADD MAPPING StructData
        WITH EVERY 500 MILLISECONDS
        ADD TAG MachineData
            WITH ADDRESS "GVL_Machine.stMachineData"
            WITH DATA_TYPE "STRUCT"
            WITH STRUCT_FIELD_DEFINITIONS "Speed:0:REAL:4,Current:4:REAL:4,Status:8:INT:2,ErrorCode:10:WORD:2"
            WITH SOURCE_TOPIC "plc/machine"
            WITH PUBLISH_MODE "JSON"

Continuous monitoring with on-demand read and write events in the same connector:

DEFINE CONNECTOR FullADSSetup WITH TYPE ADS
    ADD ADS_CONFIG
        WITH TARGET_NET_ID "192.168.1.100.1.1"
        WITH TARGET_IP "192.168.1.100"
        WITH TARGET_PORT 851
    ADD MAPPING ProcessVariables
        WITH EVERY 500 MILLISECONDS
        ADD TAG Temperature
            WITH ADDRESS "GVL_Process.rTemperature"
            WITH ADDRESS_TYPE "SYMBOL"
            WITH DATA_TYPE "REAL"
            WITH SOURCE_TOPIC "plc/temperature"
            WITH UNIT "°C"
        ADD TAG Pressure
            WITH ADDRESS "GVL_Process.rPressure"
            WITH ADDRESS_TYPE "SYMBOL"
            WITH DATA_TYPE "REAL"
            WITH SOURCE_TOPIC "plc/pressure"
            WITH UNIT "bar"
    
    ADD EVENT ReadSymbol
        WITH SOURCE_TOPIC "ads/commands/read"
        WITH DESTINATION_TOPIC "ads/responses/read"
        WITH QUERY "{operation: READ, symbol: GVL_Process.rOutput, data_type: REAL}"
    
    ADD EVENT WriteSetpoint
        WITH SOURCE_TOPIC "ads/commands/write"
        WITH DESTINATION_TOPIC "ads/responses/write"
        WITH QUERY "{operation: WRITE, symbol: GVL_Control.rSP, data_type: REAL, value: 0}"

The MAPPING continuously reads temperature and pressure. To trigger an on-demand read of the output value, publish any message to ads/commands/read. To write a setpoint, publish to ads/commands/write.

AMS route setup

The broker connects through the AMS router on the broker host. It does not create the route. Add the AMS route on the router or the PLC yourself.

On the TwinCAT system

Open TwinCAT XAE
Go to SYSTEM → Connectors
Add a static route to the broker host:
- AMS Net ID: the broker host’s AMS Net ID
- Transport Type: TCP/IP
- Address: the broker host’s IP address

LOCAL_NET_ID, LOCAL_ROUTE_TO_TARGET, TARGET_ROUTE_TO_LOCAL, TARGET_USER, and TARGET_PASSWORD are not required and are not used yet.

Troubleshooting

Connection Failed

Verify the target AMS Net ID and the route on the router or the PLC
Ensure TARGET_PORT is correct (851 for TC3, 801 for TC2)
Verify the firewall allows the ADS port (typically 48898)

Symbol Not Found

Verify symbol path matches exactly (case-sensitive)
Check symbol exists in PLC project
Ensure PLC is in RUN mode
Use AutoDiscovery to find correct symbol names

AutoDiscovery Issues

Check DISCOVERY_FILTER_INCLUDES patterns
Verify DISCOVERY_MAX_DEPTH is sufficient
For large projects, enable DISCOVERY_PARALLEL_READING
Check PLC project is compiled and deployed

Write Operations Fail

Ensure WRITABLE is set to “true”
Verify PLC variable is not constant
Check value is within MIN_VALUE/MAX_VALUE
Verify PLC is in RUN mode

Timeout Errors

Increase TIMEOUT value
Check network connectivity
Verify TwinCAT runtime is running
Reduce DISCOVERY_BATCH_SIZE if using AutoDiscovery

Next Steps

Allen-Bradley

Connect to Rockwell Automation PLCs.

OPC UA Client

Cross-platform OPC UA communication.

Quick Start

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LoT Language

Coreflux HUB

VS Code - LoT Notebooks

Coreflux Portal

Using AI with Coreflux

Product Updates

ADS Overview

Basic Syntax

AMS Net ID Basics

Connection Configuration

ADS_CONFIG Parameters

Connection Example

AutoDiscovery

AutoDiscovery Parameters

AutoDiscovery Example

TwinCAT Data Types

String sizing

TAG Configuration

Symbol-Based Addressing

Index-Based Addressing

Array Handling

Structure Handling

String sizing parameter

Event-Based Operations

Supported Operations

Query Parameters

Read Example

Write Example

Complete Examples

AMS route setup

On the TwinCAT system

Troubleshooting

Next Steps

Allen-Bradley

OPC UA Client

​ADS Overview

​Basic Syntax

​AMS Net ID Basics

​Connection Configuration

​ADS_CONFIG Parameters

​Connection Example

​AutoDiscovery

​AutoDiscovery Parameters

​AutoDiscovery Example

​TwinCAT Data Types

​String sizing

​TAG Configuration

​Symbol-Based Addressing

​Index-Based Addressing

​Array Handling

​Structure Handling

​String sizing parameter

​Event-Based Operations

​Supported Operations

​Query Parameters

​Read Example

​Write Example

​Complete Examples

​AMS route setup

​On the TwinCAT system

​Troubleshooting

​Next Steps

Allen-Bradley

OPC UA Client

ADS Overview

Basic Syntax

AMS Net ID Basics

Connection Configuration

ADS_CONFIG Parameters

Connection Example

AutoDiscovery

AutoDiscovery Parameters

AutoDiscovery Example

TwinCAT Data Types

String sizing

TAG Configuration

Symbol-Based Addressing

Index-Based Addressing

Array Handling

Structure Handling

String sizing parameter

Event-Based Operations

Supported Operations

Query Parameters

Read Example

Write Example

Complete Examples

AMS route setup

On the TwinCAT system

Troubleshooting

Next Steps