At next I connected the Atmega 328p with the 1.8 Inch display to the userport of a real C64.
I built a 2-wire serial connection from the C64 to the AVR. In the AVR is the real C64-characterset. I reduced the character-resolution to 4x5 pixels to fit the 160x128 screen.
All screen-outputs, scrolling, clearscreen, insert, del... are transmitted to the AVR.
Now I have a TFT-C64 ;-)