| Release date | 1981-12 |
|---|---|
| History | |
| Successor | μPD72120 Advanced Graphics Display Controller |
TheHigh-Performance Graphics Display Controller 7220 (commonlyμPD7220 orNEC 7220) is avideo display controller and aGraphics processing unit, capable of drawing lines, circles, arcs, and character graphics to abit-mapped display. It was developed byNippon Electric Company (NEC) in order to support theKanji character set efficiently, which explains why theAPC computer line had superior graphics compared to competing models. The chip was first used in theNEC N5200 and in later computers, such as the NECPC-9801,APC II andAPC III, the NECcomputer, the optionalgraphics module for the DEC Rainbow, theNCR Decision Mate V, theTulip System-1, and theEpson QX-10.[1]
The μPD7220 was one of the first implementations of a graphics display processor as a singleLarge Scale Integration (LSI)integrated circuit chip, enabling the design of low-cost, high-performance video graphics cards such as those fromNumber Nine Visual Technology.It was one of the best known graphics chips of the 1980s.[2]
The project was started in 1979, with trial production in 1980 and mass production starting in December 1981.[3][4] It was first used in the NECN5200 [ja] (known in North America as theNEC APC or "Advanced Personal Computer"[5]) in 1981.[6] The N5200 sported a 5 MHzIntel 8086 processor on a 16-bit bus, and came with a text-only display board using a μPD7220 (intext mode). An optional graphics-only display board, sporting a second μPD7220 chip (operating in graphics mode), "merged" the text and graphics video through an XOR port (on each of theRGB signals) in hardware. The only OS on the original NEC APC was theUCSD p-System, butCPM/86 support was added in 1982[citation needed].
In 1981, an English language paper written in 1980 by Tetsuji Oguchi, Misao Higuchi, Takashi Uno, Michiori Kamaya and Munekazu Suzuki was published in theIEEE.[7] NEC deployed the chip in other computers, such as the NEC PC-9801, and NEC's APC II and later APC III computers, and also released it to other manufacturers in Japan, starting in 1982. The same year, the 7220 was revealed in North America by NEC Information Systems, the US arm of NEC.
By 1983, it was used in other early computers, from NEC and other companies includingDigital Equipment Corporation andWang Laboratories.[8]
While most computers used memory mapped character, orbit-mapped displays, those with a μPD7220 had access to a, for the time, sophisticated graphics co-processor. The controller could either be used as a simple character display with user defined typefaces and simultaneously as an all-points addressable graphics display.
Additionally, the controller had hardware assist features for drawing straight lines and sectors of circles. It would draw pixels along a line, a circular arc or from user defined characters in under 800 ns. This released the host computer to continue other processing while the drawing operation continued.
The high-resolution capability permitted support for glyph-based languages likeJapanese that were difficult to comprehensively support with character-based displays. The large memory space, combined with hardware viewport registers permitted smooth high-speedscrolling.
Compatibility withDirect memory access hardware made it possible to movebitmaps to and from the controller memory at bus-limited rates. In this way, bitmaps could beBlitted around the display at high speed and the controller kept focused on the more complex rendering tasks.
The controller could address a maximum1024 × 1024 pixel display with four-bitcolour depth. It included alight pen interface that synchronised the pixel clock to input signals without additional processor support.
GKS was available onCP/M andMS-DOS systems and formed the basis of early 1980sCAD platforms on otherwise limited hardware platforms.
A few years after its introduction, one journalist said "The 7220 GDC chip is a component that even some of NEC's competitors have found too good to pass up."[8]When theApple Lisa was announced in 1983, the press raised questions on why the popular 7220 was not used.[9][10]Bruce Daniels pointed out that the Lisa primarily used raster graphics (known as bitmap graphics at the time), which could be implemented with less expensive hardware support. Instead, graphics primitives were written in software. Development managerWayne Rosing added that although the team knew about the 7220, it was not quite available when the design began. There were also restrictions on when the display memory could be accessed: only during certain times in thevertical refresh cycle.[9]
IBM PC compatible variants of NEC μPD7220 use theISA bus.
Variants included:
Two I/O channels are used, addressing A0 and A1. Reading A0 retrieves the 7220 status. Reading A1 fetches the first byte from the internal queue.Writing to the 7220 uses bothregisters; A1 for writing the command, A0 for writing the parameters to the queue.[1]The parts had an8-bit data path.[17]Parts were available with clocks running from 4 MHz to 5.5 MHz, which was considered relatively high-performance for the time.[10]
Perhaps the best known one is the NEC 7220.
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