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Modbus Payload Builders
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------------------------
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A collection of utilities for building and decoding
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modbus messages payloads.
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from struct import pack, unpack
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from pymodbus.constants import Endian
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class PayloadBuilder(object):
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A utility that helps build payload messages to be
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written with the various modbus messages. It really is just
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a simple wrapper around the struct module, however it saves
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time looking up the format strings. What follows is a simple
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builder = PayloadBuilder(endian=Endian.Little)
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builder.add_8bit_uint(1)
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builder.add_16bit_uint(2)
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payload = builder.tostring()
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def __init__(self, payload=None, endian=Endian.Little):
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''' Initialize a new instance of the payload builder
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:param payload: Raw payload data to initialize with
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:param endian: The endianess of the payload
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self._payload = payload or []
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''' Reset the payload buffer
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''' Return the payload buffer as a string
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:returns: The payload buffer as a string
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return ''.join(self._payload)
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''' Return the payload buffer as a list
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:returns: The payload buffer as a list
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def add_8bit_uint(self, value):
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''' Adds a 8 bit unsigned int to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 'B'
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self._payload.append(pack(fstring, value))
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def add_16bit_uint(self, value):
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''' Adds a 16 bit unsigned int to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 'H'
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self._payload.append(pack(fstring, value))
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def add_32bit_uint(self, value):
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''' Adds a 32 bit unsigned int to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 'I'
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self._payload.append(pack(fstring, value))
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def add_64bit_uint(self, value):
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''' Adds a 64 bit unsigned int to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 'Q'
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self._payload.append(pack(fstring, value))
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def add_8bit_int(self, value):
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''' Adds a 8 bit signed int to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 'b'
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self._payload.append(pack(fstring, value))
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def add_16bit_int(self, value):
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''' Adds a 16 bit signed int to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 'h'
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self._payload.append(pack(fstring, value))
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def add_32bit_int(self, value):
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''' Adds a 32 bit signed int to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 'i'
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self._payload.append(pack(fstring, value))
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def add_64bit_int(self, value):
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''' Adds a 64 bit signed int to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 'q'
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self._payload.append(pack(fstring, value))
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def add_32bit_float(self, value):
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''' Adds a 32 bit float to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 'f'
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self._payload.append(pack(fstring, value))
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def add_64bit_float(self, value):
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''' Adds a 64 bit float(double) to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 'd'
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self._payload.append(pack(fstring, value))
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def add_string(self, value):
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''' Adds a string to the buffer
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:param value: The value to add to the buffer
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fstring = self._endian + 's'
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self._payload.append(pack(fstring, c))
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class PayloadDecoder(object):
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A utility that helps decode payload messages from a modbus
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reponse message. It really is just a simple wrapper around
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the struct module, however it saves time looking up the format
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strings. What follows is a simple example::
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decoder = PayloadDecoder(self.little_endian_payload)
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first = decoder.decode_8bit_uint()
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second = decoder.decode_16bit_uint()
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def __init__(self, payload, endian=Endian.Little):
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''' Initialize a new payload decoder
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:param payload: The payload to decode with
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:param endian: The endianess of the payload
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self._payload = payload
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self._endian = endian
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''' Reset the decoder pointer back to the start
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def decode_8bit_uint(self):
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''' Decodes a 8 bit unsigned int from the buffer
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fstring = self._endian + 'B'
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handle = self._payload[self._pointer - 1:self._pointer]
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return unpack('B', handle)[0]
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def decode_16bit_uint(self):
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''' Decodes a 16 bit unsigned int from the buffer
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fstring = self._endian + 'H'
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handle = self._payload[self._pointer - 2:self._pointer]
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return unpack(fstring, handle)[0]
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def decode_32bit_uint(self):
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''' Decodes a 32 bit unsigned int from the buffer
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fstring = self._endian + 'I'
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handle = self._payload[self._pointer - 4:self._pointer]
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return unpack(fstring, handle)[0]
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def decode_64bit_uint(self):
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''' Decodes a 64 bit unsigned int from the buffer
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fstring = self._endian + 'Q'
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handle = self._payload[self._pointer - 8:self._pointer]
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return unpack(fstring, handle)[0]
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def decode_8bit_int(self):
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''' Decodes a 8 bit signed int from the buffer
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fstring = self._endian + 'b'
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handle = self._payload[self._pointer - 1:self._pointer]
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return unpack(fstring, handle)[0]
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def decode_16bit_int(self):
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''' Decodes a 16 bit signed int from the buffer
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fstring = self._endian + 'h'
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handle = self._payload[self._pointer - 2:self._pointer]
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return unpack(fstring, handle)[0]
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def decode_32bit_int(self):
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''' Decodes a 32 bit signed int from the buffer
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fstring = self._endian + 'i'
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handle = self._payload[self._pointer - 4:self._pointer]
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return unpack(fstring, handle)[0]
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def decode_64bit_int(self):
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''' Decodes a 64 bit signed int from the buffer
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fstring = self._endian + 'q'
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handle = self._payload[self._pointer - 8:self._pointer]
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return unpack(fstring, handle)[0]
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def decode_32bit_float(self):
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''' Decodes a 32 bit float from the buffer
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fstring = self._endian + 'f'
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handle = self._payload[self._pointer - 4:self._pointer]
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return unpack(fstring, handle)[0]
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def decode_64bit_float(self):
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''' Decodes a 64 bit float(double) from the buffer
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fstring = self._endian + 'd'
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handle = self._payload[self._pointer - 8:self._pointer]
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return unpack(fstring, handle)[0]
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def decode_string(self, size=1):
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''' Decodes a string from the buffer
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:param size: The size of the string to decode
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self._pointer += size
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return self._payload[self._pointer - size:self._pointer]
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#---------------------------------------------------------------------------#
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# Exported Identifiers
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#---------------------------------------------------------------------------#
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__all__ = ["PayloadBuilder", "PayloadDecoder"]
added
removed
pymodbus/payload.py
