HD44780 - squares on power on

(Moved from another thread)

When power is on, until initialization ends, HD44780 should shows squares (character FFh). That indicates that DDRAM (80x8 bits) is filled with 1.

However, I do not know how exacty RAM is filled on original HD44780, depending on how many lines LCD have.

For instance, on my 20x4 LCD with some clone, it shows 2 odd lines filled with squares (FFh), other with spaces (20h).

As per the datasheet, the entire DDRAM is filled with 20H after internal reset (power on).
But the display is Off, so it will not show data in DDRAM.

So at power On nothing is shown in the display.

Indeed. I have missed information in the datasheet that it perform auto-initialization during power on. Clones do nothing...