The MOS 6567/6569 video controller (VIC-II)
and its application in the Commodore 64
Contents
3. Description of the VIC
3.7. Text/bitmap display
3.7.3. Graphics modes
3.7.3.2. Multicolor text mode (ECM/BMM/MCM=0/0/1)
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This mode allows for displaying four-colored characters at the cost of horizontal resolution. If bit 11 of the c-data is zero, the character is displayed as in standard text mode with only the colors 0-7 available for the foreground. If bit 11 is set, each two adjacent bits of the dot matrix form one pixel. By this means, the resolution of a character of reduced to 4×8 (the pixels are twice as wide, so the total width of the characters doesn't change).

It is interesting that not only the bit combination "00" but also "01" is regarded as "background" for the sprite priority and collision detection.

c-access

Adresses
13 12 11 10 9 8 7 6 5 4 3 2 1 0
VM13 VM12 VM11 VM10 VC9 VC8 VC7 VC6 VC5 VC4 VC3 VC2 VC1 VC0

Data
11 10 9 8 7 6 5 4 3 2 1 0
MC
flag
Color of
"11" pixels
D7 D6 D5 D4 D3 D2 D1 D0

g-access

Adresses
13 12 11 10 9 8 7 6 5 4 3 2 1 0
CB13 CB12 CB11 D7 D6 D5 D4 D3 D2 D1 D0 RC2 RC1 RC0

Data
7 6 5 4 3 2 1 0
MC flag=0
8 pixels (1 bit/pixel)

"0": Background color 0 ($d021)
"1": Color from bits 8-10 of c-data
MC flag=1
4 pixels (2 bits/pixel)

"00": Background color 0 ($d021)
"01": Background color 1 ($d022)
"10": Background color 2 ($d023)
"11": Color from bits 8-10 of c-data