The video controller (Eng. Video Display Controller , VDC ) is a specialized microcircuit , which is the main component of the video image generation circuit in computers and game consoles . Some video controllers also have additional features, for example, a sound generator. Video controller microcircuits were mainly used in home computers and gaming systems of the 1980s.
Before the appearance of video controller microcircuits, the image formation circuits were completely built on discrete logic. By the mid-1970s, CRT displays had become a popular information output device for microcomputers, and the development of microcircuit production technology made it possible to implement the bulk of the image-forming circuit as a separate microcircuit. This simplified the development of such schemes, reduced the dimensions of printed circuit boards and energy consumption, and reduced the cost of end devices. Further development of video controllers led to the emergence of more complex and multifunctional devices - video processors .
The main component of the imaging circuit is always a video controller, as well as a graphics processor , but additional microcircuits can also be used - RAM for storing images, ROM for storing character graphics, and additional discrete logic (for example, shift registers) to build a complete circuit. In any case, the video controller is responsible for generating the necessary clock signals, such as vertical and horizontal synchronization signals, the backward beam signal.
Types of video
Chips of video controllers can be divided into four groups according to the principle of their work.
Video shift register is the simplest type of video controller. It generates clock signals and converts the received bytes of the video data (from the processor or DAP controller) into a sequence of bits, which together with the clock signals forms the output video signal. This type of video controller typically only supports very low-resolution raster video modes. The only example of such a general purpose video controller used in home computers is the RCA CDP1861 chip. In other home systems that also use video controllers of this type, custom chips were used - for example, the Television Interface Adapter (TIA) in the Atari 2600 game console, the BMC of the Sinclair ZX81 computer.
CRTCs ( Cathode Ray Tube Controller , CRT controller) generate clocks and read RAM used as video memory. The read data is used to form the address in the character generator ROM (for text video modes) or directly (for high-resolution graphic modes). Video controllers of this type require a large number of external components that perform video signal generation, which allows them to have a wide range of capabilities, from simple text modes to high-resolution color graphics. Such video controllers usually do not have hardware sprite support. Among the most famous video controllers of this type are Intel 8275 and Motorola 6845 chips.
Video interface controller is the next step in the development of video controllers . Almost all components of the video signal generation circuit are integrated into a single chip. Of the external elements, only analog video signal conditioning circuits are required. This category includes the Signetics 2636 chip and the chips used in Commodore's 8-bit computers (the most famous chip is MOS Technology VIC-II , used in Commodore 64 ).
Video co-processor - more complex devices that use a separate RAM as video memory and are able to not only display, but also independently process data in it. Examples of this type of video controller include the ANTIC chip used in Atari 8-bit systems, and Texas Instruments TMS9918 , Yamaha V9938, and V9958 chips used in MSX computers . This category also includes video controllers of 8-bit and 16-bit game consoles.
See also
- GPU