MateoC's code:

Code:


Questions:
1. Under label "Display_Org" why is the specific number $1038 loaded into HL?
2. Under label "Display_Window" why does reg A start at $50?
3. Under label "Write_Display_Control" why is reg A output to port $10 twice?

Sorry if the answers seem obvious, this LCD is really throwing me for a loop.

Hi GregAStar, it might be worth looking at the LCD datasheet which can be found here: http://www.displayfuture.com/Display/datasheet/controller/ILI9335.pdf

Or for some community information here: http://wikiti.brandonw.net/index.php?title=84PCSE:LCD_Controller

Write_Display_Control is a routine that writes a value in HL to the LCD REGISTER in A via the LCD control/data ports ($10 & $11). You use this to change settings for the LCD.

With regards to your questions the $1038 is the default LCD ENTRY MODE value. ENTRY MODE allows you to set various settings for the LCD like RGB/BGR, vert/horz increment, colour mode etc: http://wikiti.brandonw.net/index.php?title=84PCSE:LCD_Controller#03:_Entry_Mode

A starts at $50 because that is the WINDOW HORIZONTAL ADDRESS START. You will see that A is increased after each write, that is because $50,$51,$52,$53 are the LCD WINDOW address registers; this is how you set the 'window' that you want to write data to in the LCD. In this case the routine is drawing FULL SCREEN, so you will see the values 0,239,0,319 since it is a 320x240 LCD. Note that the LCD is actually portrait, as in, it is on its side - which is why your HORIZONTAL values are 0-239 ... even though that's the height.

And as far as writing A twice, the write to the control port takes a 16-bit value however only 8-bits are considered by the LCD. Initially we used to write a 0 and A however the 'writing A twice' optimisation was found and has been standard ever since.

I recommend have a read over the WikiTI page and if you have any more questions please let me know.