I2C for graphics displays, in my honest opnion, is just plain too slow. Even the high speed version at 400 KHz will take more than 10 times the time to transfer one byte to the graphics controller memory. The serial interface (SPI type) graphics I have used can support serial data clocking up to about 4 MHz. In addition the I2C transfers will normally impose extra bytes in the transfer protocol that may not be required in the serial clocking that the SPI type transfer may require.

Even on the Cygnal processors I have used to bit bang a LCD graphics serial inteface where the processor can be running fast at say 22.1184 MHz using 1X bus cycle timing it is possible to update a 128x64 display in about 7 msec. On an I2C display of similar size the display update could be expected to take upwards of 100 msec. This is, in my opinion, too slow for a good user inteface reaction.

Michael Karas