The MOS 6567/6569 video controller (VIC-II) and its application in the Commodore 64
Contents 3. Description of the VIC
3.10. Display Enable |
The DEN bit (Display Enable, register $d011, bit 4) serves for switching on and off the text/bitmap graphics. It is normally set. The bit affects two functions of the VIC: The Bad Lines and the vertical border unit. A Bad Line Condition can only occur if the DEN bit has been set for at least one cycle somewhere in raster line $30 (see section 3.5.). If the DEN bit is cleared, the reset input of the vertical border flip flop is deactivated (see section 3.9.). Then the upper/lower border is not turned off. So clearing the DEN bit will normally prevent Bad Lines (and thus c- and g-accesses) from occuring and make the whole screen display the border color.