Direct Connect vs Discovery

Most protocols in Nodlyn work in two ways: direct connect (you type host, topic, or address in the node Inspector) and optional Discovery (scan the network, register devices, pre-fill settings). Discovery never blocks execution — nodes read their settings at run time.

When to use direct connect

• You already know the IP, serial port, MQTT topic, or CAN interface.
• The device is on a fixed address (PLC, broker, gateway).
• You want the smallest workflow with no device registry step.

When Discovery helps

• You are onboarding many devices and want a picker in the Inspector.
• You want Device Health monitoring after registration.
• You want scan results to pre-fill node settings or add blocks to a workflow.

Examples

Modbus TCP (direct)

1. Add Modbus TCP Read Holding Registers from the palette.
2. In the Inspector set IP Address / Host (e.g. 192.168.1.10), Port 502, Unit ID, and register addresses.
3. Run Dry Run or Activate — no Discovery required.

Optional: Studio → Discovery → Industrial & building automation → Modbus TCP scan to find open port 502 hosts and accept them for pre-fill.

MQTT (direct)

1. Add MQTT Publish or MQTT Message Received.
2. Set Broker host (e.g. 192.168.1.5), port 1883, and topic (e.g. sensors/temperature).
3. Credentials go in node settings or environment variables — Discovery is only needed if you want to browse brokers on the LAN.

CAN Bus (direct)

1. Add CAN Send or CAN Receive.
2. Set Interface to your adapter (e.g. can0, vcan0 on Linux) and the frame ID.
3. Discovery can passive-listen on the bus to suggest IDs — you can always type them manually.

BACnet/IP (direct)

1. Add a BACnet read or write node from the palette.
2. In the Inspector set Device IP (e.g. 192.168.1.20), UDP port 47808, and the BACnet object type / instance or property.
3. Run Dry Run or Activate — no Discovery required.

Optional: Studio → Discovery → Industrial & building automation → BACnet Who-Is scan to find devices on the LAN and pre-fill addresses.

Printer (direct OS name)

On the Print node, enter the printer name exactly as the OS sees it (Windows share name or CUPS queue). Discovery can list printers, but it is optional.

ZigBee / Matter

Coordinator setup may still be required for ZigBee. Device address or endpoint IP can be entered manually in the Inspector; Discovery pre-fills the dropdown when devices are registered.

Summary

Approach	Best for
Direct connect	Known addresses, scripts, edge runtimes, minimal setup
Discovery	Onboarding, health tracking, Inspector pickers

See also

• Device Discovery
• Modbus TCP Request
• MQTT Publish
• Device Health