scietex.hal.serial

scietex.hal.serial is a comprehensive serial communication library designed to provide a high-level interface for managing serial ports and facilitating communication with serial devices. The package is structured into six main modules, each serving a distinct purpose:

• config: Simplifies the creation, storage, and serialization of serial port configurations.
• virtual: Enables the generation and management of virtual serial networks, ideal for testing environments and overcoming hardware limitations.
• server: Implements a Modbus server to streamline communication between various devices and applications.
• client: Provides a Modbus client that can be customized to interact with a wide range of the equipment.
• gateway: Bridges a serial RS485 bus to TCP/IP, routing Modbus/TCP requests by device id and supporting non-Modbus vendor protocols through translator plugins.
• utilities: Checksums, numeric helpers, Modbus helpers, and serial-port discovery.

Documentation

Full documentation is available at scietex-hal-serial.readthedocs.io, covering the user guide, API reference, architecture, and design notes.

See CHANGELOG.md for release history.

System Requirements

• Python: 3.10 or higher.
• Operating Systems: Compatible with Linux and macOS. The virtual serial layer uses pty.openpty and multiprocessing, so it does not run on Windows.

Installation

To install the package, execute the following command in your terminal:

pip install scietex.hal.serial

Usage

Serial Connection Configuration

Configuring a serial connection is straightforward. Here's how you can set it up:

from scietex.hal.serial import SerialConnectionConfig

ser_conf = SerialConnectionConfig(port="/dev/ttyS01")
ser_conf.baudrate = 9600

For serialization purposes, you can convert the configuration to a dictionary:

from scietex.hal.serial import SerialConnectionConfig, ModbusSerialConnectionConfig

ser_conf = SerialConnectionConfig(port="/dev/ttyS01")
ser_conf.baudrate = 9600
ser_conf.timeout = 1.0
print(ser_conf)

modbus_conf = ModbusSerialConnectionConfig(**ser_conf.to_dict())
print(modbus_conf)

Virtual Serial Network

Creating a virtual serial network is simple. Here's an example of creating a virtual serial pair:

from scietex.hal.serial import VirtualSerialPair

if __name__ == "__main__":
    vsp = VirtualSerialPair()
    vsp.start()
    # Now your virtual serial pair is ready
    print(vsp.serial_ports)

    vsp.stop()

For more complex topologies, you can use the VirtualSerialNetwork class to connect multiple virtual ports or even integrate with external physical ports:

from scietex.hal.serial import VirtualSerialNetwork, SerialConnectionConfig

if __name__ == "__main__":
    vsn1 = VirtualSerialNetwork(virtual_ports_num=3)
    vsn1.start()
    print(f"VSN 1 ports: {vsn1.serial_ports}")

    vsn2 = VirtualSerialNetwork(virtual_ports_num=2)
    vsn2.start()

    vsn2.add([SerialConnectionConfig(vsn1.serial_ports[0])])

    # Create two more virtual ports
    vsn1.create(2)

    print(f"VSN 1 ports: {vsn1.serial_ports}")
    print(f"VSN 2 ports: {vsn2.serial_ports}")

    vsn1.stop()
    vsn2.stop()

Modbus Server

To start a Modbus server, follow these steps:

import asyncio
from scietex.hal.serial import RS485Server, ModbusSerialConnectionConfig


async def main():
    config = ModbusSerialConnectionConfig("/dev/ttyS001")
    server = RS485Server(config)
    await server.start()

    await server.stop()


if __name__ == "__main__":
    asyncio.run(main())

The server supports multiple slaves, which can be added, updated, or removed dynamically.

Modbus Client

The Modbus client requires a connection configuration and a slave address. Optionally, you can provide a label for enhanced logging readability:

import asyncio
from scietex.hal.serial import (
    VirtualSerialPair,
    RS485Server,
    RS485Client,
    ModbusSerialConnectionConfig,
)


async def main():
    vsp = VirtualSerialPair()
    vsp.start()

    server_config = ModbusSerialConnectionConfig(vsp.serial_ports[0])
    client_config = ModbusSerialConnectionConfig(vsp.serial_ports[1])

    server = RS485Server(server_config)
    await server.start()

    async with RS485Client(client_config, address=1, label="My RS485 Device") as client:
        data = await client.read_registers(0, count=10)
        print(f"Registers payload: {data}")

        await client.write_register_float(register=0, value=3.14159, factor=100)
        data = await client.read_registers(0, count=10)
        print(f"Registers payload: {data}")

        value = await client.read_register_float(register=0, factor=100)
        print(f"Read value: {value}")

    await server.stop()
    vsp.stop()


if __name__ == "__main__":
    asyncio.run(main())

Modbus Gateway

The gateway bridges a serial RS485 bus to TCP/IP. It owns one serial port, accepts standard Modbus/TCP clients, and routes each request to the right device on the bus by device id. Non-Modbus vendor devices are supported through a translator plugin.

import asyncio

from scietex.hal.serial import (
    GatewayConfig,
    GatewayDeviceConfig,
    ModbusGateway,
    ModbusSerialConnectionConfig,
)


async def main():
    config = GatewayConfig(
        serial=ModbusSerialConnectionConfig("/dev/ttyUSB0", baudrate=9600),
        host="0.0.0.0",
        port=502,
        default_framer="RTU",
        devices={
            1: GatewayDeviceConfig(device_id=1, framer="RTU"),
            2: GatewayDeviceConfig(device_id=2, framer="ASCII"),
        },
    )

    gateway = ModbusGateway(config)
    await gateway.start()

    # ... serve until shutdown ...

    await gateway.stop()


if __name__ == "__main__":
    asyncio.run(main())

A TCP client then connects to host:port and issues normal Modbus/TCP requests with the target device id as the unit id. See the Gateway guide for configuration details and the non-standard protocol path.

Upgrading to 2.0

Version 2.0 makes the error contract strict by default. Read, write, and execute operations now raise ModbusOperationError on failure instead of returning None.

from scietex.hal.serial import ModbusOperationError

try:
    value = await client.read_register(0)
except ModbusOperationError as exc:
    print(f"Read failed: {exc}")

• Opt out per call. Pass raise_on_error=False to restore the 1.x behavior of returning None on failure. The parameter exists on every read/write wrapper and RS485Client method, so you can migrate incrementally.
• None is no longer a failure sentinel. Stop using if result is None to detect failure; catch ModbusOperationError instead. None now only means "no response was expected" (no_response_expected=True).
• Write→read fallback is opt-in. In 1.x, a write whose response was falsy silently fell back to a read-back. That fallback now runs only when you pass raise_on_error=False. Devices that do not echo write responses must use raise_on_error=False; under that mode a None result means "unverifiable", not necessarily "failed".
• no_response_expected=True is unchanged. It still returns None and never raises.
• Subclass authors. Overrides of read_data/process_message that call read_* methods will now propagate ModbusOperationError unless each inner call passes raise_on_error=False.

Contribution

We welcome contributions to the project! Whether it's bug fixes, feature enhancements, or documentation improvements, your input is valuable. Please feel free to submit pull requests or open issues to discuss potential changes.

License

This project is licensed under the MIT License. For more details, please refer to the LICENSE file included in the repository.