Custom Message ExampleΒΆ

#!/usr/bin/env python
"""
Pymodbus Synchronous Client Examples
--------------------------------------------------------------------------

The following is an example of how to use the synchronous modbus client
implementation from pymodbus.

It should be noted that the client can also be used with
the guard construct that is available in python 2.5 and up::

    with ModbusClient('127.0.0.1') as client:
        result = client.read_coils(1,10)
        print result
"""
import struct
# --------------------------------------------------------------------------- #
# import the various server implementations
# --------------------------------------------------------------------------- #
from pymodbus.pdu import ModbusRequest, ModbusResponse, ModbusExceptions
from pymodbus.client.sync import ModbusTcpClient as ModbusClient
from pymodbus.bit_read_message import ReadCoilsRequest
# --------------------------------------------------------------------------- #
# configure the client logging
# --------------------------------------------------------------------------- #
import logging
logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)

# --------------------------------------------------------------------------- #
# create your custom message
# --------------------------------------------------------------------------- #
# The following is simply a read coil request that always reads 16 coils.
# Since the function code is already registered with the decoder factory,
# this will be decoded as a read coil response. If you implement a new 
# method that is not currently implemented, you must register the request
# and response with a ClientDecoder factory.
# --------------------------------------------------------------------------- #


class CustomModbusResponse(ModbusResponse):
    pass


class CustomModbusRequest(ModbusRequest):

    function_code = 1

    def __init__(self, address):
        ModbusRequest.__init__(self)
        self.address = address
        self.count = 16

    def encode(self):
        return struct.pack('>HH', self.address, self.count)

    def decode(self, data):
        self.address, self.count = struct.unpack('>HH', data)

    def execute(self, context):
        if not (1 <= self.count <= 0x7d0):
            return self.doException(ModbusExceptions.IllegalValue)
        if not context.validate(self.function_code, self.address, self.count):
            return self.doException(ModbusExceptions.IllegalAddress)
        values = context.getValues(self.function_code, self.address,
                                   self.count)
        return CustomModbusResponse(values)

# --------------------------------------------------------------------------- #
# This could also have been defined as
# --------------------------------------------------------------------------- #


class Read16CoilsRequest(ReadCoilsRequest):

    def __init__(self, address):
        """ Initializes a new instance

        :param address: The address to start reading from
        """
        ReadCoilsRequest.__init__(self, address, 16)

# --------------------------------------------------------------------------- #
# execute the request with your client
# --------------------------------------------------------------------------- #
# using the with context, the client will automatically be connected
# and closed when it leaves the current scope.
# --------------------------------------------------------------------------- #


if __name__ == "__main__":
    with ModbusClient('127.0.0.1') as client:
        request = CustomModbusRequest(0)
        result = client.execute(request)
        print(result)