Output Datasources

An output datasource writes data out to an external system — a PLC, broker, or control application. Unlike input datasources, outputs have no model or tag mapping: they accept a JSON payload and deliver it to the target.

Test-write today

Output datasources currently support on-demand test writes — each write is sent individually so you can verify connectivity and addressing. Scheduled, batched production write paths are a future enhancement.

Supported outputs

Protocol	Capability
OPC-UA	Write to a node (synchronous)
MQTT	Publish to a topic (configurable QoS / retain)
Modbus TCP	Write to holding registers or coils

Configure an output

1. Create the output

   Go to Datasources → Output, click + Create, and pick the protocol.

2. Fill the connection config

   Each protocol has its own fields. Secret fields are masked as *** after saving.

   OPC-UA

   {
     "endpoint": "opc.tcp://your-plc-host:4840",
     "securityPolicy": "None",
     "authentication": "Anonymous"
   }

   MQTT

   {
     "brokerUrl": "mqtt://your-broker-host:1883",
     "topic": "devices/plc/setpoint",
     "qos": 1,
     "retain": false,
     "username": "your-username",
     "password": "your-password"
   }

   Modbus TCP

   {
     "host": "your-plc-host",
     "port": 502,
     "slaveId": 1,
     "defaultCoilAddress": 1000,
     "defaultRegisterAddress": 40001
   }

   Addresses follow the Modicon convention (coils from 1, holding registers from 40001).

3. Save and enable

   Save the output, then enable it. An output must be enabled before it will accept a test write.

Send a test write

Open the output’s details, find the Test Write action, enter a JSON payload, and send it. The result shows success or the protocol error returned by the target.

OPC-UA

Write a single node:

{
  "nodeId": "ns=2;s=Temperature",
  "value": 42.5
}

MQTT

Publish a payload:

{
  "setpoint": 65.0,
  "mode": "heating"
}

Modbus

Write one or more registers:

{
  "addresses": [
    { "address": 1000, "value": 100 },
    { "address": 1002, "value": 250 }
  ]
}

A successful write returns a success result; a protocol error returns a message such as OPC UA: node not found or Modbus: address out of range.

If something goes wrong

Symptom	Likely cause
Connection timeout	Target unreachable — check network path, host, and port (MQTT 1883, Modbus 502).
Datasource disabled error	Enable the output before sending a test write.
Node not found (OPC-UA)	Check the NodeId format and that the node exists on the server.
Address out of range (Modbus)	Stay within Modicon ranges (coils 1+, holding registers 40001+).
Admin only (403)	Test writes require an admin account.

See the Troubleshooting runbook for more.

Next steps

Connect an input Stream sensor data in to drive inference.

Monitor the runtime Latency, throughput, and KPIs.