Create a Modbus device

Add a Modbus device and start reading its registers, step by step.

This guide adds a Modbus device; other protocols follow the same flow with their own connection fields.

1. Add the device

In the project’s Tags view, click New, choose Device, then pick Modbus.

Fill in the connection:

• Name — how the device appears in the project (plus an optional custom name).
• Host — the device’s hostname or IP address.
• Port — the Modbus TCP port (default 502).
• Timeout — seconds to wait for a response (default 3).
• Unit ID — the device’s address behind a gateway, 0–255.

Leave Enabled on so THMI connects to the device, and save.

2. Add tags on the device

Open the device and click New → Tag. For each value, set:

• Function — Coils, Discrete inputs, Holding registers, or Input registers.
• Start address — where the value begins.
• Data type and, for multi-register values, the swap mode (byte/word order).
• Polling interval — how often it’s read.

Turn on Writable for coils or holding registers you want operators to be able to change.

3. Check it’s working

Back in the Tags list, the new tags show their live values as data arrives. If a multi-register number looks wrong, revisit the swap mode — see Data type and byte order.