uModbus 0.3.1

Implementation of the Modbus protocol in pure Python.

uModbus

uModbus or (μModbus) is a pure Python implementation of the Modbus protcol as described in the MODBUS Application Protocol Specification V1.1b3. The “u” or “μ” in the name comes from the the SI prefix “micro-”. uModbus is very small and lightweight. The source can be found on GitHub. Documentation is available at Read the Docs.

Quickstart

Routing Modbus requests is easy:

#!/usr/bin/env python
# scripts/examples/simple_data_store.py
import logging
from collections import defaultdict

from umodbus import get_server, conf
from umodbus.utils import log_to_stream

# Add stream handler to logger 'uModbus'.
log_to_stream(level=logging.DEBUG)

# A very simple data store which maps addresss against their values.
data_store = defaultdict(int)

# Enable values to be signed (default is False).
conf.SIGNED_VALUES = True

app = get_server('localhost', 502)


@app.route(slave_ids=[1], function_codes=[3, 4], addresses=list(range(0, 10)))
def read_data_store(slave_id, address):
    """" Return value of address. """
    return data_store[address]


@app.route(slave_ids=[1], function_codes=[6, 16], addresses=list(range(0, 10)))
def write_data_store(slave_id, address, value):
    """" Set value for address. """
    data_store[address] = value

if __name__ == '__main__':
    try:
        app.serve_forever()
    finally:
        app.shutdown()
        app.server_close()

Features

The following Modbus functions have been implemented:

• 01: Read Coils

• 02: Read Discrete Inputs

• 03: Read Holding Registers

• 04: Read Input Registers

• 05: Write Single Coil

• 06: Write Single Register

• 15: Write Multiple Coils

• 16: Write Multiple Registers

Other featues:

• Support for signed and unsigned register values.

Roadmap

uModbus is far from complete. The next, unordered list shows what is going to be implemented in the future:

• Support for all Modbus functions

• Modbus RTU

• Use asyncio for handling of requests

• Other Modbus ‘flavours’, so uModbus is able to handle 32 bit values.

License

uModbus software is licensed under Mozilla Public License. © 2015 Advanced Climate Systems.