code: async def _send_sysex(self, sysex_command, sysex_data=None):
          
          if not sysex_data:
              sysex_data = []
  
          # convert the message command and data to characters
          sysex_message = chr(PrivateConstants.START_SYSEX)
          sysex_message += chr(sysex_command)
          if len(sysex_data):
              for d in sysex_data:
                  sysex_message += chr(d)
          sysex_message += chr(PrivateConstants.END_SYSEX)
  
          for data in sysex_message:
              await self.write(data)
docs: This is a private utility method.
          This method sends a sysex command to Firmata.
  
          :param sysex_command: sysex command
  
          :param sysex_data: data for command
  
          :returns : No return value.