PROFINET Connector

Overview

The PROFINET connector enables communication with PROFINET IO devices using slot/subslot/index addressing as defined by IEC 61158. It speaks the PROFINET DCE-RPC protocol over UDP, establishing an Application Relation (AR) with the target device and exchanging record-data reads and writes.

Connector Types:

• ProfinetReader - Polls record data from PROFINET IO devices
• ProfinetWriter - Writes record data to PROFINET IO devices

Features

• ✅ PROFINET IO record data read/write via slot/subslot/index addressing
• ✅ DCE-RPC over UDP transport
• ✅ Application Relation (AR) management with automatic reconnection
• ✅ Big-endian binary decoding for all primitive types
• ✅ Wide data type support: Bool, Int8/16/32, UInt8/16/32, Float32/64, OctetString
• ✅ Configurable polling rate and per-call timeout

Basic Configuration

PROFINET Reader

{
  "type": "ProfinetReader",
  "config": {
    "endpoint": "192.168.0.50:34964",
    "pollingRate": 1000,
    "timeout": 5000
  },
  "variables": [
    {
      "key": "temperature",
      "slot": 1,
      "subslot": 1,
      "index": 100,
      "dataType": "Float32",
      "length": 4
    },
    {
      "key": "running_state",
      "slot": 1,
      "subslot": 1,
      "index": 101,
      "dataType": "Bool",
      "length": 1
    }
  ]
}

PROFINET Writer

{
  "type": "ProfinetWriter",
  "config": {
    "endpoint": "192.168.0.50:34964",
    "timeout": 5000
  },
  "variables": [
    {
      "key": "setpoint",
      "slot": 1,
      "subslot": 1,
      "index": 200,
      "dataType": "Float32",
      "length": 4
    },
    {
      "key": "enable_output",
      "slot": 1,
      "subslot": 1,
      "index": 201,
      "dataType": "Bool",
      "length": 1
    }
  ]
}

Configuration Parameters

Endpoint

The IP address and PROFINET DCE-RPC port of the target device.

{ "endpoint": "192.168.0.50:34964" }

Format: host:port. The default PROFINET DCE-RPC port is 34964. Some devices listen on alternate ports — consult the device GSD file.

Polling Rate

Required for the reader. The interval in milliseconds between successive reads.

{ "pollingRate": 1000 }

Recommended values:

• Fast diagnostic data: 100-500ms
• Process variables: 500-2000ms
• Slow telemetry: 5000ms+

PROFINET IO devices are generally tolerant of high polling rates, but the LAN and the device’s response budget are real limits.

Timeout

Optional. Per-call RPC timeout in milliseconds. Default is implementation-defined.

{ "timeout": 5000 }

Recommended values:

• Local-LAN devices: 1000-3000ms
• Devices behind a NAT or relay: 5000-10000ms

Variables

Each variable describes one record address and its on-the-wire encoding.

Variable Structure

{
  "key": "temperature",
  "slot": 1,
  "subslot": 1,
  "index": 100,
  "dataType": "Float32",
  "length": 4
}

Field	Type	Required	Description
key	string	Yes	Meddle payload key
slot	uint16	Yes	PROFINET slot number
subslot	uint16	Yes	PROFINET subslot number
index	uint16	Yes	Record index
dataType	string	Yes	Encoding (see below)
length	uint16	Yes	Number of bytes to read/write

Slot / Subslot / Index Addressing

PROFINET IO devices model their I/O as a hierarchy:

• Slot: A logical “card” inside the device. Slot 0 is reserved for the device itself (DAP)
• Subslot: A submodule within the slot. Subslot 1 is typically the primary I/O
• Index: A specific record on that submodule, defined in the device’s GSDML file

Refer to the GSDML (General Station Description Markup Language) file shipped with the device for the addressing map.

Data Types

The connector decodes record bytes using big-endian byte order (PROFINET convention):

Boolean

{ "dataType": "Bool", "length": 1 }

1 byte; 0x00 → false, anything else → true.

Integer 8/16/32

{ "dataType": "Int8",   "length": 1 }
{ "dataType": "UInt8",  "length": 1 }
{ "dataType": "Int16",  "length": 2 }
{ "dataType": "UInt16", "length": 2 }
{ "dataType": "Int32",  "length": 4 }
{ "dataType": "UInt32", "length": 4 }

All multi-byte integers are big-endian.

Float

{ "dataType": "Float32", "length": 4 }
{ "dataType": "Float64", "length": 8 }

IEEE 754 floating point, big-endian.

OctetString

{ "dataType": "OctetString", "length": 32 }

Raw bytes interpreted as a UTF-8 string. The length controls the maximum bytes read; the device’s actual response length governs how many are returned.

Supported types:

Type	Bytes	Go output type
Bool	1	bool
Int8	1	int8
UInt8	1	uint8
Int16	2	int16
UInt16	2	uint16
Int32	4	int32
UInt32	4	uint32
Float32	4	float32
Float64	8	float64
OctetString	variable	string

Data Flow

Reader Data Flow

PROFINET Device → ProfinetReader (RPC ReadRecord) → decoded values → Meddle Payload

Example:

Reader configuration:

{
  "variables": [
    { "key": "temperature", "slot": 1, "subslot": 1, "index": 100, "dataType": "Float32", "length": 4 },
    { "key": "running",     "slot": 1, "subslot": 1, "index": 101, "dataType": "Bool",    "length": 1 }
  ]
}

Output payload:

{
  "temperature": 24.7,
  "running": true
}

Writer Data Flow

Meddle Payload → ProfinetWriter (encode + RPC WriteRecord) → PROFINET Device

Example:

Input payload:

{
  "setpoint": 75.0,
  "enable_output": true
}

Each key matching a configured variable.key is encoded according to its dataType and written via WriteRecord. Keys not in the variables list are ignored.

Common Use Cases

1. Reading Diagnostic Data from a PROFINET IO Module

{
  "type": "ProfinetReader",
  "config": {
    "endpoint": "192.168.0.50:34964",
    "pollingRate": 2000,
    "timeout": 5000
  },
  "variables": [
    { "key": "module_status",   "slot": 1, "subslot": 1, "index": 1000, "dataType": "UInt16", "length": 2 },
    { "key": "temperature_c",   "slot": 1, "subslot": 1, "index": 1001, "dataType": "Float32", "length": 4 },
    { "key": "uptime_seconds",  "slot": 0, "subslot": 1, "index": 2000, "dataType": "UInt32", "length": 4 },
    { "key": "device_name",     "slot": 0, "subslot": 1, "index": 3000, "dataType": "OctetString", "length": 64 }
  ]
}

2. Sending Setpoints to a Drive

{
  "type": "ProfinetWriter",
  "config": {
    "endpoint": "192.168.0.60:34964",
    "timeout": 3000
  },
  "variables": [
    { "key": "speed_rpm",    "slot": 1, "subslot": 1, "index": 100, "dataType": "Int32",   "length": 4 },
    { "key": "torque_limit", "slot": 1, "subslot": 1, "index": 101, "dataType": "Float32", "length": 4 },
    { "key": "enable",       "slot": 1, "subslot": 1, "index": 102, "dataType": "Bool",    "length": 1 }
  ]
}

3. Reading from Multiple Submodules

{
  "type": "ProfinetReader",
  "config": {
    "endpoint": "192.168.0.50:34964",
    "pollingRate": 1000,
    "timeout": 5000
  },
  "variables": [
    { "key": "input_card_1_value", "slot": 1, "subslot": 1, "index": 100, "dataType": "Int16",   "length": 2 },
    { "key": "input_card_2_value", "slot": 2, "subslot": 1, "index": 100, "dataType": "Int16",   "length": 2 },
    { "key": "input_card_3_value", "slot": 3, "subslot": 1, "index": 100, "dataType": "Int16",   "length": 2 },
    { "key": "device_temp",        "slot": 0, "subslot": 1, "index": 200, "dataType": "Float32", "length": 4 }
  ]
}

Troubleshooting

ErrProfinetConnect at Startup

Problem: Cannot establish an Application Relation (AR) with the device

Solutions:

1. Verify the device IP and port: ping 192.168.0.50 and nc -zv -u 192.168.0.50 34964
2. Confirm the device’s PROFINET stack is running and not in fault state
3. Check that the device is not already in an AR with another controller (PROFINET devices typically allow a limited number of concurrent ARs)
4. Use a tool like Wireshark with the PROFINET dissector to inspect the connect handshake

ErrProfinetReadFailed on a Specific Variable

Problem: One variable returns an error while others succeed

Solutions:

1. Verify the slot/subslot/index against the device’s GSDML file
2. Check the configured length matches the actual record size on the device
3. Some indexes are write-only or protected — consult the device documentation

insufficient data for <type>

Problem: Device returned fewer bytes than the data type requires

Solutions:

1. Increase length for the variable to match the device’s response size
2. For OctetString, length is a maximum; for fixed-width types it must equal the type’s byte count
3. Some devices pad responses — ensure length is at least the minimum required (e.g. 4 for Float32)

Connection Lost Mid-Read

Problem: ErrProfinetDisconnected errors appear after a period of normal operation

Solutions:

1. The connector automatically reconnects on the next poll cycle — expect a brief gap and resume
2. If disconnections are frequent, check the PROFINET network for cable issues, switch overload, or duplicate IP addresses
3. Increase timeout for high-latency networks

Wrong Values for Multi-Byte Types

Problem: Int32/Float values are obviously wrong (huge magnitudes, NaN, wrong sign)

Solutions:

1. PROFINET wire format is always big-endian. There is no byte-order toggle. If your device documentation claims little-endian, check whether it’s a vendor-specific record (vendor records may use other encodings — decode externally with a Transform)
2. Confirm the data type matches the GSDML declaration

Best Practices

1. Always Consult the GSDML

Slot, subslot, and index assignments are device-specific. The GSDML is the canonical source — don’t infer addressing.

2. Use Slot 0 / Subslot 1 for Device-Level Records

Conventionally:

• Slot 0 = DAP (Device Access Point) — device identity, diagnostics, system records
• Slot N, Subslot 1 = primary I/O of the Nth I/O submodule

3. Be Conservative with Polling Rates

PROFINET IO devices process record data via the application layer, not the cyclic I/O channel — so polling too aggressively can starve the cyclic path. 500-2000ms is typical for record polling.

4. Handle Reconnects Gracefully Downstream

Use a Filter or Validation connector after the reader to gate further processing during reconnection windows.

5. Encode Writes Defensively

When publishing setpoints, pre-clamp values upstream with a Transform or Reshape so out-of-range data never reaches the writer. PROFINET devices may reject (or worse, accept) extreme values inconsistently.

Example Workflows

PROFINET Drive Monitoring Pipeline

ProfinetReader → Validation → Reshape → Predictive → InfluxDb2Writer
                                              └→ Isa182 → Alert

1. ProfinetReader: Reads temperature, current, vibration from a drive at 1Hz
2. Validation: Ensures all signals are present and numeric
3. Reshape: Tags with asset_id, line, area
4. Predictive: Computes trends and RUL for temperature and vibration
5. InfluxDb2Writer: Long-term storage
6. Isa182: Triggers alarm on degrading health score
7. Alert: Notifies maintenance

Closed-Loop PROFINET Setpoint Control

ScriptReader (control logic) → ProfinetWriter
ProfinetReader → ScriptReader (feedback loop)

A Script connector reads PROFINET inputs, computes a control output, and writes it back via the PROFINET writer — a classic supervisory loop.

Related Connectors

• Modbus - Alternative industrial fieldbus
• Siemens S7 - Direct S7 protocol for Siemens PLCs
• OPC UA - Modern abstraction over PROFINET/S7 data
• Validation - Gate downstream during reconnects
• Predictive - Predictive analytics on PROFINET signals

Additional Resources

• PROFINET Specification (PI)
• IEC 61158 - PROFINET protocol standard
• GSDML Specification - General Station Description Markup Language
• Wireshark PROFINET Dissector