Video Display Controller
Encyclopedia
A Video Display Controller or VDC is an integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

 which is the main component in a video signal generator
Video signal generator
A video signal generator is a type of signal generator which outputs predetermined video and/or television oscillation waveforms, and other signals used in the synchronization of television devices and to stimulate faults in, or aid in parametric measurements of, television and video systems. There...

, a device responsible for the production of a TV
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

 video signal
Composite video
Composite video is the format of an analog television signal before it is combined with a sound signal and modulated onto an RF carrier. In contrast to component video it contains all required video information, including colors in a single line-level signal...

 in a computing or game system. Some VDCs also generate an Audio signal
Audio signal
An audio signal is an analog representation of sound, typically as an electrical voltage. Audio signals may be synthesized directly, or may originate at a transducer such as a microphone, musical instrument pickup, phonograph cartridge, or tape head. Loudspeakers or headphones convert an electrical...

, but in that case it's not their main function.

VDCs were most often used in the old home-computers
Home computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...

 of the 80s, but also in some early video game systems.

The VDC is always the main component of the video signal generator logic, but sometimes there are also other supporting chips used, such as RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...

 to hold the pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....

 data
Bitmap
In computer graphics, a bitmap or pixmap is a type of memory organization or image file format used to store digital images. The term bitmap comes from the computer programming terminology, meaning just a map of bits, a spatially mapped array of bits. Now, along with pixmap, it commonly refers to...

, ROM
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...

 to hold character fonts
Computer font
A computer font is an electronic data file containing a set of glyphs, characters, or symbols such as dingbats. Although the term font first referred to a set of metal type sorts in one style and size, since the 1990s it is generally used to refer to a scalable set of digital shapes that may be...

, or perhaps some discrete logic such as shift register
Shift register
In digital circuits, a shift register is a cascade of flip flops, sharing the same clock, which has the output of any one but the last flip-flop connected to the "data" input of the next one in the chain, resulting in a circuit that shifts by one position the one-dimensional "bit array" stored in...

s were necessary to build a complete system. In any case, it's the VDC's responsibility to generate the timing of the necessary video signals, such as the horizontal and vertical synchronisation signal
Component video sync
Component video requires an extra synchronization signal to be sent along with the video. Component video sync signals can be sent in several different ways:...

s, and the blanking interval signal.

Most often the VDC chip is completely integrated in the logic of the main computer system, (its video RAM appears in the memory map
Memory map
In computer science, a memory map is a structure of data that indicates how memory is laid out. Memory maps can have a different meaning in different parts of the operating system....

 of the main CPU), but sometimes it functions as a coprocessor
Coprocessor
A coprocessor is a computer processor used to supplement the functions of the primary processor . Operations performed by the coprocessor may be floating point arithmetic, graphics, signal processing, string processing, or encryption. By offloading processor-intensive tasks from the main processor,...

 that can manipulate the video RAM contents independently

Video Display Controllers vs. Video Display Processors and Graphics processing units

The difference between a VDC and the more modern Video Display Processor
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...

 (VDP) is not that the VDCs could not generate graphics
Raster graphics
In computer graphics, a raster graphics image, or bitmap, is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium...

, but they did not have the special hardware accelerator
Hardware acceleration
In computing, Hardware acceleration is the use of computer hardware to perform some function faster than is possible in software running on the general-purpose CPU...

s to create 2D
2D computer graphics
2D computer graphics is the computer-based generation of digital images—mostly from two-dimensional models and by techniques specific to them...

 and 3D
3D computer graphics
3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...

 images, while a typical 1990s VDP does have at least some form of hardware graphics acceleration. Also VDCs often had special hardware for the creation of "sprites
Sprite (computer graphics)
In computer graphics, a sprite is a two-dimensional image or animation that is integrated into a larger scene...

", a function that in more modern VDP chips is done with the "Bit Blitter
Blitter
In a computer system, a blitter is a circuit, sometimes as a coprocessor or a logic block on a microprocessor, that is dedicated to the rapid movement and modification of data within that computer's memory...

" using the "Bit blit
Bit blit
Bit BLIT is a computer graphics operation in which several bitmaps are combined into one using a raster operator....

" function.

One example of a typical Video Display Processor is the "VDP2 32-bit background and scroll plane video display processor" of the Sega Saturn
Sega Saturn
The is a 32-bit fifth-generation video game console that was first released by Sega on November 22, 1994 in Japan, May 11, 1995 in North America, and July 8, 1995 in Europe...

.
Another example is the Advanced Graphics Architecture
Advanced Graphics Architecture
Advanced Graphics Architecture is the third generation Amiga graphic chip set, first used in the Amiga 4000 in 1992. AGA was codenamed the Pandora chipset by Commodore International internally....

 (AGA) chip that was used for the improved graphics of the later generation Amiga
Amiga
The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...

 computers.

This said, it is not completely clear when a "Video chip" is a "Video Display Controller" and when it is a "Video Display Processor". For example, the TMS9918 is sometimes called a "Video Display Controller" and sometimes a "Video Display Processor". In general however a "Video Display Processor" has some power to "Process" the contents of the Video RAM (filling an area of RAM for example), while a "Video Display Controller" only controls the timing of the Video synchronisation signals and the access to the Video RAM.

The Graphics processing unit
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...

 (GPU) goes one step further than the VDP and normally also supports 3D functionality. It is the chip that is now used in modern personal computers.

Types of Video Display Controllers

Video Display controllers can be (arbitrarily) divided in several different types (here listed from simple to complex);
  • Video shifters, or "Video shift register based systems" (there is no generally agreed upon name for these type of devices) are the most simple type of video controllers; they are, (directly or indirectly) responsible for the video timing signals, but they normally do not access the Video RAM directly. They get the video data from the main CPU, a byte at a time, and convert it to a serial bitstream (hence the technical name "Video shifter"). This serial data stream is then used, together with the synchronisation signals, to output a (colour) video signal. The main CPU needs to do the bulk of the work. Normally these chips only support a very low resolution Raster graphics
    Raster graphics
    In computer graphics, a raster graphics image, or bitmap, is a data structure representing a generally rectangular grid of pixels, or points of color, viewable via a monitor, paper, or other display medium...

     mode.

  • A CRTC, or Cathode Ray Tube Controller, generates the video timings and reads video data from a RAM attached to the CRTC, to output it via an external character generator ROM, (for text mode
    Text mode
    Text mode is a kind of computer display mode in which the content of the screen is internally represented in terms of characters rather than individual pixels. Typically, the screen consists of a uniform rectangular grid of character cells, each of which contains one of the characters of a...

    s) or directly, (for high resolution graphics modes) to the video output shift register. Because the actual capabilities of the video generator depend to a large degree on the external logic, video generator based on a CRTC chip can have a wide range of capabilities. From very simple (text mode only) systems to very high resolution systems supporting a wide range of colours. Sprites however are normally not supported by these systems.

  • Video interface controllers are much more complex than CRT controllers, and the external circuitry that is needed with a CRTC is embedded in the video controller chip. Sprites are often supported, as are (RAM based) character generators
    Character encoding
    A character encoding system consists of a code that pairs each character from a given repertoire with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the transmission of data through telecommunication networks or storage of text in...

     and video RAM dedicated to colour attributes
    Character encoding
    A character encoding system consists of a code that pairs each character from a given repertoire with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the transmission of data through telecommunication networks or storage of text in...

     and pallette registers
    Palette (computing)
    In computer graphics, a palette is either a given, finite set of colors for the management of digital images , or a small on-screen graphical element for choosing from a limited set of choices, not necessarily colors .Depending on the context In computer graphics, a palette is either a given,...

     (Color lookup tables
    CLUT
    A colour look-up table is a mechanism used to transform a range of input colours into another range of colours. It can be a hardware device built into an imaging system or a software function built into an image processing application...

    ) for the high-resolution and/or text-modes.

  • Video coprocessors have their own internal CPU dedicated to reading (and writing) their own video RAM, and converting the contents of this video RAM to a video signal. The main CPU can give commands to the coprocessor, for example to change the video modes or to manipulate the video ram contents. The video coprocessor also controls the (most often RAM based) character generator, the colour attribute RAM, Palette registers and the Sprite logic (as long as these exist of course).

List of example VDCs

Examples of Video Display Controllers are:

Video shifters
  • The RCA CDP1861 was a very simple chip, built in CMOS
    CMOS
    Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...

     technology (which was unusual for the mid '70's) to complement the RCA 1802
    RCA 1802
    The RCA CDP1802, also known as the COSMAC , is an 8-bit CMOS microprocessor introduced by RCA in early 1976. It is being by Intersil Corporation as a high-reliability microprocessor...

     microprocessor, it was mainly used in the COSMAC VIP
    COSMAC VIP
    The COSMAC VIP was an early microcomputer that was aimed at video games. For a price of US$275, it could be purchased from RCA by mail order. It came in kit form, and had to be assembled. Its dimensions were 22 x 28 cm, and it had a RCA 1802 processor; along with a crystal clock operating at 1.76...

    . It could only support a very low resolution monochrome graphic mode.
  • The "Television Interface Adapter
    Television Interface Adapter
    The Television Interface Adaptor is the custom computer chip that is the heart of the Atari 2600 game console, generating the screen display, sound effects, and reading input controllers. Its design was widely affected by an attempt to reduce the amount of RAM needed to operate the display...

     (TIA) is the custom video chip that is the heart of the Atari 2600
    Atari 2600
    The Atari 2600 is a video game console released in October 1977 by Atari, Inc. It is credited with popularizing the use of microprocessor-based hardware and cartridges containing game code, instead of having non-microprocessor dedicated hardware with all games built in...

     games console, a very primitive chip that relied on the 6502 microprocessor to do most of the work, also was used to generate the audio.


CRT Controllers
  • The Intel 8275 CRT controller was not used in any mainstream system, but was used in some S100 bus systems.
  • The Motorola 6845
    Motorola 6845
    The Motorola 6845 is a video address generator first introduced by Motorola and used among others in the Videx VideoTerm display cards for the Apple II computers, the MDA and CGA video adapters for the IBM PC, in the Amstrad CPC and the BBC Micro. Its functionality was duplicated and extended by...

     is a video address generator first introduced by Motorola
    Motorola
    Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...

     and used for the Amstrad CPC
    Amstrad CPC
    The Amstrad CPC is a series of 8-bit home computers produced by Amstrad between 1984 and 1990. It was designed to compete in the mid-1980s home computer market dominated by the Commodore 64 and the Sinclair ZX Spectrum, where it successfully established itself primarily in the United Kingdom,...

    , and the BBC Micro
    BBC Micro
    The BBC Microcomputer System, or BBC Micro, was a series of microcomputers and associated peripherals designed and built by Acorn Computers for the BBC Computer Literacy Project, operated by the British Broadcasting Corporation...

    . It was later used for almost all the early video adapters for the PC, such as the MDA, CGA
    Color Graphics Adapter
    The Color Graphics Adapter , originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter, introduced in 1981, was IBM's first color graphics card, and the first color computer display standard for the IBM PC....

     and EGA adapters. In all later VGA
    Video Graphics Array
    Video Graphics Array refers specifically to the display hardware first introduced with the IBM PS/2 line of computers in 1987, but through its widespread adoption has also come to mean either an analog computer display standard, the 15-pin D-subminiature VGA connector or the 640×480 resolution...

     compatible adapters the function of the 6845 is reproduced inside the Video Chip, so in a sense all current IBM PC compatible
    IBM PC compatible
    IBM PC compatible computers are those generally similar to the original IBM PC, XT, and AT. Such computers used to be referred to as PC clones, or IBM clones since they almost exactly duplicated all the significant features of the PC architecture, facilitated by various manufacturers' ability to...

     PC's still incorporate the logic of the 6845 CRTC.


Video Interface Controllers
  • The Signetics 2636 and 2637 are video controllers best known for their use in the Interton VC 4000
    VC 4000
    The VC 4000 is an early 8-bit cartridge-based game console released in Germany in 1978 by Interton. The console is quite obscure outside Germany, but many software compatible systems can be found in many European countries...

     and Emerson Arcadia 2001
    Arcadia 2001
    The Arcadia 2001 is a second-generation 8-bit console released by Emerson Radio Corp. The game library was composed of 51 unique games and about 10 variations. The graphic quality is similar to that of the Intellivision and the Odyssey²....

     respectively.
  • The MC6847
    MC6847
    The MC6847 is a video display generator first introduced by Motorola and used in the TRS-80 Color Computer, Dragon 32/64, Laser 200 and Acorn Atom among others. It is a relatively simple display generator compared to other display chips of the time. It is capable of displaying text and graphics...

     is a video display generator (VDG) first introduced by Motorola and used in the TRS-80 Color Computer
    TRS-80 Color Computer
    The Radio Shack TRS-80 Color Computer was a home computer launched in 1980. It was one of the earliest of the first generation of computers marketed for home use in English-speaking markets...

    , Dragon 32/64
    Dragon 32/64
    The Dragon 32 and Dragon 64 are home computers that were built in the 1980s. The Dragons are very similar to the TRS-80 Color Computer , and were produced for the European market by Dragon Data, Ltd., in Port Talbot, Wales, and for the US market by Tano of New Orleans, Louisiana...

    , Laser 200 and Acorn Atom
    Acorn Atom
    The Acorn Atom was a home computer made by Acorn Computers Ltd from 1980 to 1982 when it was replaced by the BBC Micro and later the Acorn Electron....

     among others.
  • The MOS Technology 6560 (NTSC) and 6561 (PAL)
    MOS Technology VIC
    The VIC , specifically known as the MOS Technology 6560 / 6561 , is the integrated circuit chip responsible for generating video graphics and sound in the Commodore VIC-20 home computer...

     are known as the Video Interface Controller (VIC) and used in the Commodore VIC-20
    Commodore VIC-20
    The VIC-20 is an 8-bit home computer which was sold by Commodore Business Machines. The VIC-20 was announced in 1980, roughly three years after Commodore's first personal computer, the PET...

    .
  • The MOS Technology 6567/8562/8564 (NTSC versions) and 6569/8565/8566 (PAL)
    MOS Technology VIC-II
    The VIC-II , specifically known as the MOS Technology 6567/8562/8564 , 6569/8565/8566 , is the microchip tasked with generating Y/C/composite video graphics and DRAM refresh signals in the Commodore 64 and C128 home computers.Succeeding MOS's original VIC , the VIC-II was one of the two chips...

     were known as the VIC-II and were used in the Commodore 64
    Commodore 64
    The Commodore 64 is an 8-bit home computer introduced by Commodore International in January 1982.Volume production started in the spring of 1982, with machines being released on to the market in August at a price of US$595...

    .
  • The MOS Technology 8563
    MOS Technology 8563
    The 8563 Video Display Controller was an integrated circuit produced by MOS Technology. It was used in the Commodore 128 computer to generate an 80-column RGB video display...

    /8568 was used in the Commodore 128
    Commodore 128
    The Commodore 128 home/personal computer was the last 8-bit machine commercially released by Commodore Business Machines...

     to create the 80 column text mode, together with the normal VIC-II chip for the C64 compatible video modes.
  • The MOS Technology 7360
    MOS Technology TED
    The 7360 Text Editing Device was an integrated circuit made by MOS Technology, Inc. It was a video chip that also contained sound generation hardware, DRAM refresh circuitry, interval timers, and keyboard input handling. It was designed for the Commodore Plus/4 and 16...

     Text Editing Device (TED) was used in the Commodore Plus/4
    Commodore Plus/4
    The Commodore Plus/4 was a home computer released by Commodore International in 1984. The "Plus/4" name refers to the four-application ROM resident office suite ; it was billed as "the productivity computer with software built-in"...

    , Commodore 16
    Commodore 16
    The Commodore 16 was a home computer made by Commodore with a 6502-compatible 8501 CPU, released in 1984. It was intended to be an entry-level computer to replace the VIC-20 and it often sold for 99 USD...

     and Commodore 116 computers and had an integrated audio capability.
  • The Picture Processing Unit
    Picture Processing Unit
    The PPU , more specifically known as Ricoh RP2C02 / RP2C07 , is the microprocessor in the Nintendo Entertainment System responsible for generating video signals from graphic data stored in memory....

     was a video co-processor designed by Ricoh
    Ricoh
    or Ricoh, is a Japanese company that was established in 1936 on February 6th, as , a company in the RIKEN zaibatsu. Its headquarters is located in Ricoh Building in Chūō, Tokyo....

     for Nintendo
    Nintendo
    is a multinational corporation located in Kyoto, Japan. Founded on September 23, 1889 by Fusajiro Yamauchi, it produced handmade hanafuda cards. By 1963, the company had tried several small niche businesses, such as a cab company and a love hotel....

    's use in the Famicom and Nintendo Entertainment System
    Nintendo Entertainment System
    The Nintendo Entertainment System is an 8-bit video game console that was released by Nintendo in North America during 1985, in Europe during 1986 and Australia in 1987...

    . It was connected to 2048 byte
    Byte
    The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...

    s of dedicated video RAM, and had a dedicated address bus that allowed additional RAM or ROM to be accessed from the game cartridge. A scrollable playfield of 256×240 pixels was supported, along with a display list of 64 OBJs (sprites), of which 8 could be displayed per scanline.
  • The TMS9918 is known as the Video Display Processor (VDP) and was first designed for the Texas Instruments
    Texas Instruments
    Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...

     TI-99/4, but was later also used in systems like the MSX
    MSX
    MSX was the name of a standardized home computer architecture in the 1980s conceived by Kazuhiko Nishi, then Vice-president at Microsoft Japan and Director at ASCII Corporation...

     (MSX-1), ColecoVision
    ColecoVision
    The ColecoVision is Coleco Industries' second generation home video game console which was released in August 1982. The ColecoVision offered arcade-quality graphics and gaming style, and the means to expand the system's basic hardware...

    , Memotech MTX series, and for the Sega
    Sega
    , usually styled as SEGA, is a multinational video game software developer and an arcade software and hardware development company headquartered in Ōta, Tokyo, Japan, with various offices around the world...

     SG-1000
    SG-1000
    The SC-3000 was the computer equivalent of the SG-1000.The SC-3000 sold for ¥29,800 in 1983 and was marketed as a computer for beginners...

     and SC-3000.
  • The NEC µPD7220
    NEC µPD7220
    The High-Performance Graphics Display Controller 7220 is a video interface controller developed by NEC and used among others in its APC III computers and the Epson QX-10.A CMOS variant is called µPD72020.-Internals:...

    . Used in some high-end graphics boards for the IBM PC in the mid 80s, notably in products from Number 9 Computer Company
    Number Nine Visual Technology
    Number Nine Visual Technology Corporation was a manufacturer of video graphics chips and cards from 1982 to 1999. Number Nine developed the first 128-bit graphics processor , as well as the first 256-color and 16.8 million color cards....

    .


Video Coprocessors
  • The ANTIC
    ANTIC
    Alphanumeric Television Interface Controller is an early video system chip used in the Atari 8-bit family of microcomputers as well as the Atari 5200 in the 1980s. The chip was patented by Atari, Inc. in 1981...

     (Alpha-Numeric Television Interface Circuit) was an early video system chip used in the Atari 8-bit family
    Atari 8-bit family
    The Atari 8-bit family is a series of 8-bit home computers manufactured from 1979 to 1992. All are based on the MOS Technology 6502 CPU and were the first home computers designed with custom coprocessor chips...

     of microcomputer
    Microcomputer
    A microcomputer is a computer with a microprocessor as its central processing unit. They are physically small compared to mainframe and minicomputers...

    s. It could read a "Display list
    Display list
    A display list is a series of graphics commands that define an output image. The image is created by executing the commands....

    " with its own built in CPU and use this data to generate a complex video signal.
  • The Yamaha V9938
    Yamaha V9938
    The Yamaha V9938 is a Video Display Controller used in the Geneve 9640 enhanced TI-99/4A clone, as well as MSX 80s home computers ....

     is an improved version of the TMS9918, and was mainly used in the MSX
    MSX
    MSX was the name of a standardized home computer architecture in the 1980s conceived by Kazuhiko Nishi, then Vice-president at Microsoft Japan and Director at ASCII Corporation...

    2.
  • The Yamaha V9958
    Yamaha V9958
    The Yamaha V9958 is a Video Display Controller used in MSX 80s home computers. More specifically, the "TIM" upgrade to the TI-99/4A, MSX 2+ and MSX turbo R....

     is the Video Display Processor (VDP) mainly used in the MSX 2+ and MSX turbo R computers.

Alternatives to using a VDC chip

Note that many older home-computer did not use a VDP-chip, but built the whole video display controller from a lot of discrete logic
Transistor-transistor logic
Transistor–transistor logic is a class of digital circuits built from bipolar junction transistors and resistors. It is called transistor–transistor logic because both the logic gating function and the amplifying function are performed by transistors .TTL is notable for being a widespread...

 chips, (examples are the Apple II
Apple II
The Apple II is an 8-bit home computer, one of the first highly successful mass-produced microcomputer products, designed primarily by Steve Wozniak, manufactured by Apple Computer and introduced in 1977...

, PET
Commodore PET
The Commodore PET was a home/personal computer produced from 1977 by Commodore International...

, and TRS-80
TRS-80
TRS-80 was Tandy Corporation's desktop microcomputer model line, sold through Tandy's Radio Shack stores in the late 1970s and early 1980s. The first units, ordered unseen, were delivered in November 1977, and rolled out to the stores the third week of December. The line won popularity with...

). Because these methods are very flexible the video display generators could be very capable, (or extremely primitive, depending of the quality of the design) but also needed a lot of components.

Many early systems used some form of an early programmable logic array
Programmable logic array
A programmable logic array is a kind of programmable logic device used to implement combinational logic circuits. The PLA has a set of programmable AND gate planes, which link to a set of programmable OR gate planes, which can then be conditionally complemented to produce an output...

 to create a video system, examples include the ZX Spectrum
ZX Spectrum
The ZX Spectrum is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research Ltd...

 and ZX-81 systems and Elektronika BK-0010 but there were many others. Early implementations are often very primitive, but later implementations could result in fairly advanced video systems like the one in the SAM Coupé
SAM Coupé
The SAM Coupé is an 8-bit British home computer that was first released in late 1989. It is commonly considered a clone of the Sinclair ZX Spectrum computer, since it features a compatible screen mode and emulated compatibility, and it was marketed as a logical upgrade from the Spectrum...

.

These systems could thus build a very capable system with relatively few components, but the low transistor count of early programmable logic meant that the capabilities of early PLA based systems often were less impressive than those using the video interface controllers or video coprocessors that were available at the same time. Later PLA solutions, like those using CPLDs or FPGAs could result in much more advanced video systems, surpassing those built using off the shelf components.

An often used hybrid solution was to use a video interface controller (often the Motorola 6845
Motorola 6845
The Motorola 6845 is a video address generator first introduced by Motorola and used among others in the Videx VideoTerm display cards for the Apple II computers, the MDA and CGA video adapters for the IBM PC, in the Amstrad CPC and the BBC Micro. Its functionality was duplicated and extended by...

) as a basis and expand its capabilities with programmable logic or an ASIC
ASIC
ASIC may refer to:* Application-specific integrated circuit, an integrated circuit developed for a particular use, as opposed to a customised general-purpose device.* ASIC programming language, a dialect of BASIC...

.
An example of such a hybrid solution is the original VGA card, that used an 6845 in combination with an ASIC, that is the reason why all current VGA based video systems still use the hardware register
Hardware register
In digital electronics, especially computing, a hardware register stores bits of information, in a way that all the bits can be written to or read out simultaneously.The hardware registers inside a central processing unit are called processor registers....

s that were provided by the 6845.

Later solutions

With Moore's law
Moore's Law
Moore's law describes a long-term trend in the history of computing hardware: the number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years....

 working, integrated circuits became more and more complex. The simple Video Display Controllers were slowly replaced by chips that had built-in video processing logic such as Blitter
Blitter
In a computer system, a blitter is a circuit, sometimes as a coprocessor or a logic block on a microprocessor, that is dedicated to the rapid movement and modification of data within that computer's memory...

s and other logic to manipulate the video RAM contents to do things like drawing lines, filling areas, or drawing fonts. Later chips also got special hardware to draw filled triangles to support 3D images, gained hardware Z-buffers
Z-buffering
In computer graphics, z-buffering is the management of image depth coordinates in three-dimensional graphics, usually done in hardware, sometimes in software. It is one solution to the visibility problem, which is the problem of deciding which elements of a rendered scene are visible, and which...

 and many other methods to accelerate the drawing of 3D pictures. Current Video generator chips almost always are "Graphics processing units" (GPU's) Entry-level PCs today commonly have the video display integrated into the motherboard chipset, which "steals" some system RAM for the display. The performance of such a system is not as good as one with dedicated video hardware.

See also

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK