Selecting the correct ILI9341 Drive Mode for STM32F407 using FSMC
Look at the table on page 26. The difference is in the pin allocations on the 18-bit data bus. In 8, 9 and 16 bit interface mode, there are more data bus pins than required, and the two modes select which pins are left unused. In 8080-I mode, the data is aligned to the least significant bit of the bus and the most significant bits are left unused, while in 8080-II mode the data is aligned to the most significant bit, and the least significant bits are unused.