def data(self, c):
        """Send byte of data to display."""
        if self._spi is not None:
            # SPI write.
            self._gpio.set_high(self._dc)
            self._spi.write([c])
        else:
            # I2C write.
            control = 0x40   # Co = 0, DC = 0
            self._i2c.write8(control, c)