Data model configuration

The simulator data model represent the registers and parameters of the simulated devices. The data model is defined using SimData and SimDevice before starting the server and cannot be changed without restarting the server.

SimData defines a group of continuous identical registers. This is the basis of the model, multiple SimData are used to mirror the physical device.

SimDevice defines device parameters and a list of SimData. The list of SimData can be added as shared registers or as 4 separate blocks as defined in modbus. SimDevice are used to simulate a single device, while a list of SimDevice simulates a multipoint line (rs485 line) or a serial forwarder.

A server consist of communication parameters and a list of SimDevice

Usage examples

#!/usr/bin/env python3
"""Pymodbus server datamodel examples.

This file shows examples of how to configure the datamodel for the server/simulator.

There are different examples showing the flexibility of the datamodel.

**REMARK** This code is experimental and not integrated into production.

"""

from pymodbus.constants import DataType
from pymodbus.simulator import SimData, SimDevice


def define_datamodel():
    """Define register groups.

    Coils and discrete inputs are modeled as bits representing a relay in the device.
    There are no real difference between coils and discrete inputs, but historically
    they have been divided. Please be aware the coils and discrete inputs are addressed differently
    in shared vs non-shared models.
    - In a non-shared model the address is the bit directly.
      It can be thought of as if 1 register == 1 bit.
    - In a shared model the address is the register containing the bits.
      1 register == 16bit, so a single bit CANNOT be addressed directly.

    Holding registers and input registers are modeled as int/float/string representing a sensor in the device.
    There are no real difference between holding registers and input registers, but historically they have
    been divided.
    Please be aware that 1 sensor might be modeled as several register because it needs more than
    16 bit for accuracy (e.g. a INT32).
    """
    # SimData can be instantiated with positional or optional parameters:
    assert SimData(
            5, 10, 17, DataType.REGISTERS
        ) == SimData(
            address=5, values=17, count=10, datatype=DataType.REGISTERS
        )

    # Define a group of coils/discrete inputs non-shared (address=15..31 each 1 bit)
    #block1 = SimData(address=15, count=16, values=True, datatype=DataType.BITS)
    # Define a group of coils/discrete inputs shared (address=15..31 each 16 bit)
    #block2 = SimData(address=15, count=16, values=0xFFFF, datatype=DataType.BITS)

    # Define a group of holding/input registers (remark NO difference between shared and non-shared)
    #block3 = SimData(10, 1, 123.4, datatype=DataType.FLOAT32)
    #block4 = SimData(17, count=5, values=123, datatype=DataType.INT64)
    block5 = SimData(1027, 1, "Hello ", datatype=DataType.STRING)

    block_def = SimData(0, count=1000, datatype=DataType.REGISTERS)

    # SimDevice can be instantiated with positional or optional parameters:
    assert SimDevice(
            5,
            [block_def, block5],
        ) == SimDevice(
            id=5, type_check=False, simdata=[block_def, block5]
        )

    # SimDevice can define either a shared or a non-shared register model
    SimDevice(id=1, type_check=False, simdata=[block_def, block5])
    #SimDevice(2, False,
    #          block_coil=[block1],
    #          block_discrete=[block1],
    #          block_holding=[block2],
    #          block_input=[block3, block4])
    # Remark: it is legal to reuse SimData, the object is only used for configuration,
    # not for runtime.

    # id=0 in a SimDevice act as a "catch all". Requests to an unknown id is executed in this SimDevice.
    #SimDevice(0, block_shared=[block2])


def main():
    """Combine setup and run."""
    define_datamodel()

if __name__ == "__main__":
    main()

Class definitions

class pymodbus.constants.DataType(value)

Register types, used to define of a group of registers.

This is the types pymodbus recognizes, actually the modbus standard do NOT define e.g. INT32, but since nearly every device contain e.g. values of type INT32, it is available in pymodbus, with automatic conversions to/from registers.

INT16 = 1: 1 integer == 1 register

UINT16 = 2: 1 positive integer == 1 register

INT32 = 3: 1 integer == 2 registers

UINT32 = 4: 1 positive integer == 2 registers

INT64 = 5: 1 integer == 4 registers

UINT64 = 6: 1 positive integer == 4 register

FLOAT32 = 7: 1 float == 2 registers

FLOAT64 = 8: 1 float == 4 registers

STRING = 9: 1 string == (len(string) / 2) registers

BITS = 10: 16 bits == 1 register

REGISTERS = 11: Registers == 2 bytes (identical to UINT16)

INVALID = 12: 1 register

Bases: object

Configure a group of continuous identical values/registers.

Examples:

SimData(
    address=100,
    count=5,
    values=12345678
    datatype=DataType.INT32
)
SimData(
    address=100,
    values=[1, 2, 3, 4, 5]
    datatype=DataType.INT32
)

Each SimData defines 5 INT32 in total 10 registers (address 100-109)

SimData(
    address=0,
    count=1000,
    values=0x1234
    datatype=DataType.REGISTERS
)

Defines a range of registers (addresses) 0..999 each with the value 0x1234.

SimData(
    address=0,
    count=1000,
    datatype=DataType.INVALID
)

Defines a range of registers (addresses) 0..999 each marked as invalid.

SimData(
    address=100,
    count=16,
    values=True
    datatype=DataType.BITS
)
SimData(
    address=100,
    values=[True] * 16
    datatype=DataType.BITS
)
SimData(
    address=100,
    values=0xffff,
    datatype=DataType.BITS
)
SimData(
    address=100,
    values=[0xffff],
    datatype=DataType.BITS
)

Each SimData defines 16 BITS (coils), with value True.

Value are stored in registers (16bit is 1 register), the address refers to the register, unless in non-shared mode where the address refers to the coil.

address: int: Address of first register, starting with 0 (identical to the requests)

count: int = 1

Count of datatype e.g.

count=3 datatype=DataType.REGISTERS is 3 registers.

count=3 datatype=DataType.INT32 is 6 registers.

count=1 datatype=DataType.STRING, values=”ABCD” is 2 registers

count=2 datatype=DataType.STRING, values=”ABCD” is 4 registers

if values= is a list, count will be applied to the whole list, e.g.

count=3 datatype=DataType.REGISTERS values=[3,2] is 6 registers.

count=3 datatype=DataType.INT32 values=[3,2] is 12 registers.

count=2 datatype=DataType.STRING, values=[“ABCD”, ‘EFGH’] is 8 registers

values: int | float | str | bytes | list[int | float | str | bytes | bool] = 0: Value/Values of datatype, will automatically be converted to registers, according to datatype.

datatype: DataType = 12: Used to check access and convert value to/from registers or mark as invalid.

readonly: bool = False: Mark register(s) as readonly.

build_registers(endian: tuple[bool, bool], string_encoding: str) → list[list[int]]: Convert values= to registers.

class pymodbus.simulator.SimDevice(id: int, simdata: SimData | list[SimData] | tuple[list[SimData], list[SimData], list[SimData], list[SimData]], type_check: bool = False, endian: tuple[bool, bool] = (True, True), string_encoding: str = 'utf-8', identity: ModbusDeviceIdentification | None = None, action: Callable[[int, int, list[int], list[int] | None], Awaitable[list[int] | None | ExceptionResponse]] | None = None)

Bases: object

Configure a device with parameters and registers.

Registers are defined as a list of SimData objects (block).

Some old devices uses 4 distinct blocks instead of a shared block, to support these devices, define the 4 blocks and add them as a set.

When using distinct blocks, coils and discrete inputs are addressed differently, each register represent 1 coil/relay

Device with shared registers:

SimDevice(
    id=1,
    simdata=[SimData(...)]
)

Device with non-shared registers:

SimDevice(
    id=1,
    simdata=([SimData(...)], [SimData(...)], [SimData(...)], [SimData(...)]),
)

A server can be configured with either a single SimDevice or a list of SimDevice to simulate a multipoint line.

id: int

Address/id of device

id=0 means all devices, except those specifically defined.

simdata: SimData | list[SimData] | tuple[list[SimData], list[SimData], list[SimData], list[SimData]]

List of register blocks (shared registers) or a tuple with 4 lists of register blocks (non-shared registers)

The tuple is defined as:

(<coils>, <discrete inputs>, <holding registers>, <input registers>)

<coils> / <discrete inputs> have addressing calculated differently:: address register = address / 16 to find the coil at address count is number of coils, so registers returned are count +15 / 16.

..tip:: addresses not defined are invalid and will produce an ExceptionResponse ..warning:: lists are sorted on starting address.

type_check: bool = False

Enforce type checking, if True access are controlled to be conform with datatypes.

Type violations like e.g. reading INT32 as INT16 are returned as ExceptionResponses, as well as being logged.

endian: tuple[bool, bool] = (True, True)

Change endianness.

Word order is not defined in the modbus standard and thus a device that uses little-endian is still within the modbus standard.

Byte order is defined in the modbus standard to be big-endian, however it is definable to test non-standard modbus devices

..tip:: Content (word_order, byte_order), True means big-endian.

string_encoding: str = 'utf-8': String encoding

identity: ModbusDeviceIdentification | None = None: Set device identity

action: Callable[[int, int, list[int], list[int] | None], Awaitable[list[int] | None | ExceptionResponse]] | None = None

Function to call when registers are being accessed.

Example function:

async def my_action(
    function_code: int,
    start_address: int,
    current_registers: list[int],
    new_registers: list[int] | None) -> list[int] | ExceptionResponse:

    return registers
     or
    return None

action, is called with current registers and if write request also the new registers. result updates registers and if read request returned to the client.

new_registers is None for read requests.

if return is None it indicates no change.

Tip

use functools.partial to add extra parameters if needed.

build_device() → tuple[int, list[int], list[int]] | dict[str, tuple[int, list[int], list[int]]]: Check simdata and built runtime structure.