Hi David,
The GC9A01 driver datasheet provided with the product can be downloaded at https://www.buydisplay.com/download/ic/GC9A01A.pdf
I have developed a ST7789 driver before and the LCD initialization command codes are at least documented in the ST7789 datasheet.
The CG9A01 datasheet (linked to above) is missing a multitude of command codes that are used in the demo code, attached in the original first post.
Like I say in the original post, I am sure if I compiled and ran the demo it would work, but to not be able to document what most of the GC9A01 LCD initialization code is actually doing is a annoying, due to the command codes not being documented in the datasheet.
Thanks for responding
Mark