Кибернетика, автоматика, протоколы

https://github.com/DreamSourceLab/DSView/blob/master/libsigrokdecode4DSL/decoders/modbus/pd.py

def parse_write_multiple(self):
        '''Function 15 and 16 are almost the same, so we can parse them both
        using one function.'''
        self.mimumum_length = 8
        function = self.data[1].data
        if function == 15:
            data_unit = 'Coils'
            max_outputs = 0x07B0
            long_address_offset = 10001
        elif function == 16:
            data_unit = 'Registers'
            max_outputs = 0x007B
            long_address_offset = 30001
        self.puti(1, 'function',
            'Function {}: Write Multiple {}'.format(function, data_unit))
        starting_address = self.half_word(2)
        # Some instruction manuals use a long form name for addresses, this is
        # listed here for convienience.
        address_name = long_address_offset + starting_address
        self.puti(3, 'address',
            'Start at address 0x{:X} / {:d}'.format(starting_address,
                                                    address_name))
        quantity_of_outputs = self.half_word(4)
        if quantity_of_outputs <= max_outputs:
            self.puti(5, 'data',
                'Write {} {}'.format(quantity_of_outputs, data_unit))
        else:
            self.puti(5, 'error',
                'Bad value: {} {}. Max is {}'.format(quantity_of_outputs,
                                                     data_unit, max_outputs))
        self.check_crc(7)

CRC для этой команды они считают не глядя на размеры пакета. В других местах логика бывает погибче " self.check_crc(bytecount + 4)"