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
3.7.3.7. Invalid bitmap mode 1 (ECM/BMM/MCM=1/1/0)
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This mode also only displays a black screen, but the pixels can also be read out with the sprite collision trick.

The structure of the graphics is basically as in standard bitmap mode, but the bits 9 and 10 of the g-addresses are always zero due to the set ECM bit and so the graphics is - roughly said - made up of four "sections" that are each repeated four times.

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
unused

g-access

Adresses
13 12 11 10 9 8 7 6 5 4 3 2 1 0
CB13 VC9 VC8 0 0 VC5 VC4 VC3 VC2 VC1 VC0 RC2 RC1 RC0

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

"0": Black (background)
"1": Black (foreground)