# RegisterDef

## pydantic model RegisterDef[source]

Bases: `BaseModel`

Definition of a Modbus register.

> **Note**
>
> - Swap options control byte ordering for multi-byte values:
>   - [`byte_swap`](https://dev.nominal.io/instro/ref/protocols/instro.modbus.types.RegisterDef.md#instro.modbus.types.RegisterDef.byte_swap "instro.modbus.types.RegisterDef.byte_swap"): swap bytes within each 16-bit word
>   - [`word_swap`](https://dev.nominal.io/instro/ref/protocols/instro.modbus.types.RegisterDef.md#instro.modbus.types.RegisterDef.word_swap "instro.modbus.types.RegisterDef.word_swap"): swap 16-bit words (for 32-bit and 64-bit types)
>   - [`long_swap`](https://dev.nominal.io/instro/ref/protocols/instro.modbus.types.RegisterDef.md#instro.modbus.types.RegisterDef.long_swap "instro.modbus.types.RegisterDef.long_swap"): swap 32-bit longs (for 64-bit types only)
> - All swap options default to False (big-endian / network byte order).
> - [`scale`](https://dev.nominal.io/instro/ref/protocols/instro.modbus.types.RegisterDef.md#instro.modbus.types.RegisterDef.scale "instro.modbus.types.RegisterDef.scale") is not allowed for coils and discrete inputs.

### field name: str [Required]

Unique name/alias for this register

### field description: str | None = None

### field starting_address: int [Required]

Constraints:
:   - **ge** = 0
    - **le** = 65535

### field register_type: RegisterType = 'holding'

### field data_type: DataType = 'uint16'

### field byte_swap: bool = False

### field word_swap: bool = False

### field long_swap: bool = False

### field scale: ScaleType | None = None

### field bitmap: list[BitDef] | None = None

### field poll: bool = True

### field write_min: float | int | None = None

### field write_max: float | int | None = None

### field write_value_map: dict[str, int | float] | None = None

### field read_group: str | None = None