The MOS 6567/6569 video controller (VIC-II) and its application in the Commodore 64
Contents 3. Description of the VIC
3.1. Block diagram |
The following block diagram gives an overview over the internal structure of the VIC and the independently working function units: The lightpen unit is not shown. As you can see, the "Raster counter X/Y" plays a central role. This is no surprise as the complete screen display and all bus accesses are synchronized by it. It is important to note that the units for display and for the needed memory accesses are separate from each other for the sprites as well as for the graphics. There is a data buffer between the two units that holds the read graphics data and buffers it for the display circuits. In the normal operation of the VIC, the functions of the two units are so closely tied to each other that they appear like a single function block. By appropriate programming, however, you can decouple the circuits and e.g. display graphics without previously having read data (in this case, the data which are still in the buffer are displayed).