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
3.7.3.6. Invalid text mode (ECM/BMM/MCM=1/0/1)
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Setting the ECM and MCM bits simultaneously doesn't select one of the "official" graphics modes of the VIC but creates only black pixels. Nevertheless, the graphics data sequencer internally generates valid graphics data that can trigger sprite collisions even in this mode. By using sprite collisions, you can also read out the generated data (but you cannot see anything, the screen is black). You can, however, only distinguish foreground and background pixels as you cannot get color information from sprite collisions.

The generated graphics is similar to that of the multicolor text mode, but the character set is limited to 64 characters as in ECM mode.

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
unused 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 0 0 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": Black (background)
"1": Black (foreground)
MC flag=1
4 pixels (2 bits/pixel)

"00": Black (background)
"01": Black (background)
"10": Black (foreground)
"11": Black (foreground)