Editing MOS Technology VIC-II (section)

===Programming===
[[Image:Supratechnic Demo.gif|frame|right|''Supratechnic'', a [[type-in program]] published by ''[[COMPUTE!'s Gazette]]'' in November 1988, showcases the careful use of [[raster interrupt]]s to display information outside of the standard screen borders (here: the upper and lower border).]]

The VIC-II is programmed by manipulating its 47 control registers (up from 16 in the VIC), memory mapped to the range {{mono|$D000}}&ndash;{{mono|$D02E}} in the C64 address space. Of all these registers, 34 deal exclusively with [[sprite (computer graphics)|sprite]] control (sprites being called MOBs, from "Movable Object Blocks", in the VIC-II documentation). Like its predecessor, the VIC-II handles [[light pen]] input, and with help from the C64's standard character ROM, provided the original [[PETSCII]] character set from 1977 on a similarly dimensioned display as the 40-column [[Commodore PET|PET]] series.

By reloading the VIC-II's control registers via machine code hooked into the [[raster interrupt]] routine (the scanline interrupt), one can program the chip to generate significantly more than 8 concurrent sprites (a process known as [[sprite multiplexing]]), and generally give every program-defined slice of the screen different scrolling, resolution and color properties. The hardware limitation of 8 sprites per scanline can be increased further by letting the sprites flicker rapidly on and off. Mastery of the raster interrupt is essential in order to unleash the VIC-II's capabilities. Many [[Demo (computer programming)|demo]]s and some later games would establish a fixed "lock-step" between the CPU and the VIC-II so that the VIC registers could be manipulated at exactly the right moment, but the reliance on raster interrupts to ensure proper synchronization could be reduced and their overhead minimized.