#Stream from a PLC over Modbus

Read a PLC, power meter or controller over Modbus TCP or RTU. Each register you map becomes a channel.

#Before you start

• For TCP, the device's address and port (usually 502). For RTU, its serial port (/dev/ttyUSB0, COM3) and line settings.
• Its unit ID — usually 1.
• Its register map, from the device manual.

#Steps

1. Open Connectors, search for modbus, and press Install.

2. Open Inputs, press Add input, and choose modbus.

3. Fill the fields:

   Field	Example
   Device name	plc1 — channels read /modbus/plc1/…
   Connection (host:port or serial device)	192.168.1.60:502 or /dev/ttyUSB0
   Transport	tcp (default) or rtu
   Unit ID	1
   Poll rate (Hz)	10

   For rtu, also set Serial baud rate (RTU), Serial parity (RTU), Serial stop bits (RTU) and Serial data bits (RTU). Defaults are 9600 8N1.

4. Paste your device's map into Register map (JSON), one entry per value:

   Copy[{"alias": "temp", "address": 0, "kind": "input", "dtype": "i16",
     "scale": {"gain": 0.1, "offset": 0}, "unit": "degC"},
    {"alias": "pump_speed_sp", "address": 10, "kind": "holding",
     "dtype": "u16", "unit": "rpm", "writable": true}]

   Key	Value
   alias	the channel's last path segment
   address	zero-based — a manual's 40001 is 0
   kind	input · holding · coil · discrete
   dtype	u16 · i16 · u32 · i32 · f32; bool for coil and discrete
   scale	gain and offset into engineering units
   writable	true to accept setpoints

5. Press Test connection. It reads the first mapped register. A pass means the device answered.

6. Press Add & start.

7. In Channels, type a name and unit for each, such as temp → bearing temperature, degC.

#Check it worked

On Inputs, the row counts samples at about your poll rate. On Live, each value shows as /modbus/plc1/<alias>.

Updated November 6, 2026