Continuing with the protocol, once the LCD is initialized it is ready to draw.  Drawing works by first defining a region to draw and then streaming pixel data to fill that region.  It is confusing at first, but if done properly is more efficient than pixel-by-pixel drawing.  A region is simply a rectangular area on the screen.  We'll say it begins at point (X1,Y1) and ends at point (X2, Y2).  Once defined, the LCD controller will fill in pixels from left to right starting at (X1, Y1).  When it reaches the edge of the region, it will jump to the next line [in my example, (X1, Y1+1) ].  It does this until it reaches (X2, Y2) at which it stops accepting data.  If you only want to draw one pixel, you simply set (X1, Y1) and (X2, Y2) to the pixel you want to draw.  This defines the region as a single pixel.  Any data sent after the first pixel's worth of data is discarded.

To define a region, you must send these commands in the following order:

PASET (Hex 0x2B) - Page Address Set
Data Y1 - The starting Y position
Data Y2 - The ending Y position

CASET (Hex 0x2A) - Column Address Set
Data X1 - The starting X position
Data X2 - The ending X position

RAMWR (Hex 0x2C) - RAM Write - Start sending pixel data after this command

<Pixel Data> - Formatting described below

After the screen is ready to accept pixel data, you must send color data for each pixel in order.  In the default color mode (0x03, 12 bits per pixel) color data uses 12 bits.  This means that you can send 2 pixels worth of data for every 3 bytes.  If you are only sending one pixel, you only need to send 2 bytes.  The 2-pixels-per-3-bytes format is shown below:

RRRR GGGG | BBBB RRRR | GGGG BBBB

If only sending one pixel, you may use this format instead:

XXXX RRRR | GGGG BBBB (X means "don't care", can be either 0 or 1, these bits are discarded)

In C, you may use this code to output 2-pixels-per-3-bytes format, color1 and color2 are 16-bit values (ints in AVR GCC)

(color_lcd_send_data(char dat) is a function that outputs a data byte to the LCD)

color_lcd_send_data(color1 >> 4);
color_lcd_send_data(((color1&0x0F)<<4)|(color2>>8));
color_lcd_send_data(color2);

This code is simplified for 1-pixel-2-bytes format for single-pixel writes:

color_lcd_send_data(color >> 4);
color_lcd_send_data(color<<4);