CharPad 2.7 User Manual - Subchrist Software, 2020.
High-resolution character images.
High-resolution character images are 8x8 pixels in size and use a bit-depth of 1 bit-per-pixel.
They can therefore use two colours...
• Background colour (0-15), defined in the VIC colour register at memory address $d021 (53281). Pixel = "0".
• Foreground colour (0-15), screen-position dependent, defined in the colour-RAM matrix from $d800 (55296). Pixel = "1".
Notes...
In high-resolution character-mode (without using raster tricks), the Commodore 64 can display up to 256 different character images on-screen.
The background colour is the same for all displayed character images.
The colour-RAM matrix (a 40x25 byte array, only the low nybbles are usable) is available from memory address $d800 (55296).
The following formula can be used to determine the memory address for a particular colour-RAM cell...
55296 + (y * 40) + x