Multicolor character mode

Multicolor character mode is a feature of the MOS Technology VIC which allows more than two colors per character.

Characters are always eight pixels wide. In standard color mode, each character in Character ROM is made up one byte per line, with the bits set to determine if the background or foreground will be set for individual pixels. In multicolor character mode, each line is four two-pixel-wide blocks, with two bits used to set the color of each block:

• 0 (binary 00) = Background
• 1 (binary 01) = Border color
• 2 (binary 10) = Foreground
• 3 (binary 11) = Auxiliary color

The background, border, and auxiliary colors are set via VIC registers. All three have a single value and change screen-wide, while the foreground can be set for each character via the Color RAM. The background and border colors are always seen, while the auxiliary color is only used for multicolor characters. Notably, while the foreground and border colors are set via three-bit numbers and allow for an eight-color palette, the background and auxiliary colors used four-bit values, unlocking an extra eight colors not normally seen.

Multicolor character mode is enabled by setting bit 3 in the color values in Color RAM. As as result, it is individually enabled or disabled on a per-character basis.

External links

• www dot atarimagazines dot com/compute/issue36/037_Programming_Multicolor_Characters_On_The_VIC.php