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Bit Reading Request/Response messages
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from pymodbus.pdu import ModbusRequest
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from pymodbus.pdu import ModbusResponse
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from pymodbus.pdu import ModbusExceptions as merror
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from pymodbus.utilities import pack_bitstring, unpack_bitstring
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class ReadBitsRequestBase(ModbusRequest):
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''' Base class for Messages Requesting bit values '''
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def __init__(self, address, count, **kwargs):
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''' Initializes the read request data
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:param address: The start address to read from
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:param count: The number of bits after 'address' to read
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ModbusRequest.__init__(self, **kwargs)
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self.address = address
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''' Encodes a request pdu
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:returns: The encoded pdu
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return struct.pack('>HH', self.address, self.count)
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def decode(self, data):
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''' Decodes a request pdu
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:param data: The packet data to decode
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self.address, self.count = struct.unpack('>HH', data)
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''' Returns a string representation of the instance
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:returns: A string representation of the instance
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return "ReadBitRequest(%d,%d)" % (self.address, self.count)
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class ReadBitsResponseBase(ModbusResponse):
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''' Base class for Messages responding to bit-reading values '''
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_rtu_byte_count_pos = 2
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def __init__(self, values, **kwargs):
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''' Initializes a new instance
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:param values: The requested values to be returned
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ModbusResponse.__init__(self, **kwargs)
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self.bits = values or []
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''' Encodes response pdu
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:returns: The encoded packet message
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result = pack_bitstring(self.bits)
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packet = struct.pack(">B", len(result)) + result
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def decode(self, data):
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''' Decodes response pdu
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:param data: The packet data to decode
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self.byte_count = struct.unpack(">B", data[0])[0]
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self.bits = unpack_bitstring(data[1:])
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def setBit(self, address, value=1):
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''' Helper function to set the specified bit
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:param address: The bit to set
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:param value: The value to set the bit to
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self.bits[address] = (value != 0)
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def resetBit(self, address):
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''' Helper function to set the specified bit to 0
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:param address: The bit to reset
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self.setBit(address, 0)
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def getBit(self, address):
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''' Helper function to get the specified bit's value
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:param address: The bit to query
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:returns: The value of the requested bit
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return self.bits[address]
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''' Returns a string representation of the instance
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:returns: A string representation of the instance
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return "ReadBitResponse(%d)" % len(self.bits)
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class ReadCoilsRequest(ReadBitsRequestBase):
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This function code is used to read from 1 to 2000(0x7d0) contiguous status
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of coils in a remote device. The Request PDU specifies the starting
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address, ie the address of the first coil specified, and the number of
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coils. In the PDU Coils are addressed starting at zero. Therefore coils
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numbered 1-16 are addressed as 0-15.
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def __init__(self, address=None, count=None, **kwargs):
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''' Initializes a new instance
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:param address: The address to start reading from
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:param count: The number of bits to read
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ReadBitsRequestBase.__init__(self, address, count, **kwargs)
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def execute(self, context):
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''' Run a read coils request against a datastore
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Before running the request, we make sure that the request is in
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the max valid range (0x001-0x7d0). Next we make sure that the
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request is valid against the current datastore.
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:param context: The datastore to request from
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:returns: The initializes response message, exception message otherwise
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if not (1 <= self.count <= 0x7d0):
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return self.doException(merror.IllegalValue)
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if not context.validate(self.function_code, self.address, self.count):
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return self.doException(merror.IllegalAddress)
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values = context.getValues(self.function_code, self.address, self.count)
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return ReadCoilsResponse(values)
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class ReadCoilsResponse(ReadBitsResponseBase):
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The coils in the response message are packed as one coil per bit of
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the data field. Status is indicated as 1= ON and 0= OFF. The LSB of the
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first data byte contains the output addressed in the query. The other
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coils follow toward the high order end of this byte, and from low order
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to high order in subsequent bytes.
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If the returned output quantity is not a multiple of eight, the
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remaining bits in the final data byte will be padded with zeros
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(toward the high order end of the byte). The Byte Count field specifies
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the quantity of complete bytes of data.
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def __init__(self, values=None, **kwargs):
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''' Intializes a new instance
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:param values: The request values to respond with
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ReadBitsResponseBase.__init__(self, values, **kwargs)
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class ReadDiscreteInputsRequest(ReadBitsRequestBase):
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This function code is used to read from 1 to 2000(0x7d0) contiguous status
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of discrete inputs in a remote device. The Request PDU specifies the
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starting address, ie the address of the first input specified, and the
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number of inputs. In the PDU Discrete Inputs are addressed starting at
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zero. Therefore Discrete inputs numbered 1-16 are addressed as 0-15.
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def __init__(self, address=None, count=None, **kwargs):
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''' Intializes a new instance
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:param address: The address to start reading from
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:param count: The number of bits to read
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ReadBitsRequestBase.__init__(self, address, count, **kwargs)
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def execute(self, context):
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''' Run a read discrete input request against a datastore
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Before running the request, we make sure that the request is in
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the max valid range (0x001-0x7d0). Next we make sure that the
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request is valid against the current datastore.
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:param context: The datastore to request from
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:returns: The initializes response message, exception message otherwise
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if not (1 <= self.count <= 0x7d0):
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return self.doException(merror.IllegalValue)
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if not context.validate(self.function_code, self.address, self.count):
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return self.doException(merror.IllegalAddress)
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values = context.getValues(self.function_code, self.address, self.count)
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return ReadDiscreteInputsResponse(values)
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class ReadDiscreteInputsResponse(ReadBitsResponseBase):
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The discrete inputs in the response message are packed as one input per
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bit of the data field. Status is indicated as 1= ON; 0= OFF. The LSB of
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the first data byte contains the input addressed in the query. The other
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inputs follow toward the high order end of this byte, and from low order
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to high order in subsequent bytes.
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If the returned input quantity is not a multiple of eight, the
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remaining bits in the final data byte will be padded with zeros
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(toward the high order end of the byte). The Byte Count field specifies
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the quantity of complete bytes of data.
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def __init__(self, values=None, **kwargs):
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''' Intializes a new instance
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:param values: The request values to respond with
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ReadBitsResponseBase.__init__(self, values, **kwargs)
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#---------------------------------------------------------------------------#
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#---------------------------------------------------------------------------#
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"ReadCoilsRequest", "ReadCoilsResponse",
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"ReadDiscreteInputsRequest", "ReadDiscreteInputsResponse",
added
removed
pymodbus/bit_read_message.py
