# Modbus RTU

A connection type for [`ModbusDevice`](https://dev.nominal.io/instro/library/protocols/modbus.md)

![Modbus RTU](https://dev.nominal.io/instro/_images/ModbusRTU.png)

Modbus RTU is a connection type for [`ModbusDevice`](https://dev.nominal.io/instro/library/protocols/modbus.md), not a separate driver class: set `"transport": "rtu"` in the config’s connection block, or pass a `ModbusRTUTransport` explicitly. The Python code is identical to Modbus TCP; only the connection block changes.

## Creating a [`ModbusDevice`](https://dev.nominal.io/instro/ref/protocols/instro.modbus.ModbusDevice.md#instro.modbus.ModbusDevice "instro.modbus.ModbusDevice") over RTU

```json
{
  "version": 1,
  "protocol": "modbus",
  "device": {
    "name": "field_sensor",
    "description": "RS-485 field temperature sensor"
  },
  "connection": {
    "transport": "rtu",
    "port": "/dev/ttyUSB0",
    "baudrate": 9600,
    "parity": "N",
    "stopbits": 1,
    "bytesize": 8,
    "timeout": 2.0,
    "unit_id": 1
  },
  "registers": [
    {
      "name": "temperature",
      "starting_address": 0,
      "register_type": "input",
      "data_type": "float32",
      "poll": true
    }
  ]
}
```

```python
from instro.modbus import ModbusDevice

device = ModbusDevice(config="field_sensor.json")
device.open()
```

Parameters and methods specific to [`ModbusDevice`](https://dev.nominal.io/instro/ref/protocols/instro.modbus.ModbusDevice.md#instro.modbus.ModbusDevice "instro.modbus.ModbusDevice") can be found in the [Reference](https://dev.nominal.io/instro/ref.md).