Packs the command into *bytes*

        :param seq: sequence number
        :rtype: bytes

def _pack(self, seq='SEQUNSET'):
        '''
        Packs the command into *bytes*

        :param seq: sequence number
        :rtype: bytes
        '''

        return 'AT*{clsname}={seq}{argl_wc}\r'.format(
            clsname=type(self).__name__,
            seq=seq,
            argl_wc=b''.join(self._iter_packed_with_comma()).decode()
        ).encode()