Write the specified byte value to the IODIR registor.  If no value
        specified the current buffered value will be written.

def _write_iodir(self, iodir=None):
        """Write the specified byte value to the IODIR registor.  If no value
        specified the current buffered value will be written.
        """
        if iodir is not None:
            self.iodir = iodir
        self.i2c.write_list(self.IODIR, self.iodir)