I will put a more detailed spec about programming CGA here.
The video memory for the CGA framebuffer is supposed to be placed at real-mode segment 0xB800. 1 bit per pixel means that every byte packs 8 pixels, one for each bit respectively. The most significant bit controls the left-most pixel.
The video memory layout in my [[Poqet pc|poqet]] for 640x200x1bpp is a bit weird. Firstly, the screen is partitioned into odd and even scanlines, and odd (if you start numbering them at 1) lines comes first in video memory, and even lines comes last:
0: (0,0) ... (639,0)
80: (0,2) ... (639,2)
...
7920: (0,198) ... (639,198)
8000: Pixels 0 - 639 of the indicator-bar (which is 4 pixels high, but only addressable per column)
Here are 72 bytes that does I dont know what.
8152: (0,1) ... (639,1)
8232: (0,3) ... (639,3)
...
I dont know what those "missing" 72 bytes are yet. I also dont know how CGA is normally arranged in memory.
