Atmega328P UART Levels

[GolamMostafa]

@MarkT

The V_IH is 0.6 Vcc, ie 3.0V for a 5.0V supply, just compatible with 3.3V logic

Is "VIH = 0.6xVcc" to make compatible with 3.3V logic or to take care of "Electrical Road Noise"?