docs: def write_port(self, port, value):
          """ Use a whole port as a bus and write a byte to it.
  
          :param port: Name of the port ('A' or 'B')
          :param value: Value to write (0-255)
          """
          if port == 'A':
              self.GPIOA = value
          elif port == 'B':
              self.GPIOB = value
          else:
              raise AttributeError('Port {} does not exist, use A or B'.format(port))
          self.sync()