>>What is the maximum dot clock ?
The LCD_DOTCLK is max 75MHz, see LCDIF_CLK_ROOT in Reference Manual, please!
>>what is the maximum RGB dots per HSYNC that can be supported ?
HSYNC is determined by dotclock, resolution & Frames per second.
>>Wanting to use 1280 pixel horizontal in RGB666
LCDIF on i.MXRT1050 supprts WXGA(1280x800), which is max resolution, you can calculate dot clock according to requirments, assume 60fps & 50fps & 30fps:
-- dot clock = 1280x800 * 60 * 130% =79.872MHz. > 75MHz
dot clock = 1280x800 * 50 * 130% =51.2MHz. < 75MHz
dot clock = 1280x800 * 30 * 130% =39.936MHz. < 75MHz
[ 30% is reserved for "blank" ]
Taking 30fps an example:
-- display data (Byte) = 1280x800 *3*30 = 92.16MB/s
If external SDRAM can work at 166MHz, the resolution should be OK.
So you can evaluate it according to your requirments.
Have a nice day!