NEC µPD7220
The High-Performance Graphics Display Controller 7220 (commonly μPD7220 or NEC 7220) is a video display processor capable of drawing lines, circles, arcs, and character graphics to a bit-mapped display. It was developed by NEC in order to support the Kanji character set efficiently, which explains why the APC computer line had such superior graphics compared to competing models. The chip was also used in later computers, such as the NEC , PC-9801 APC II and APC III computers, the NECcomputer, the optional graphics module for the DEC Rainbow, the NCR Decision Mate V, the Tulip System-1,  and the Epson QX-10.

The μPD7220 was one of the first implementations of a graphics display processor as a single Large Scale Integration (LSI) integrated circuit chip, enabling the design of low-cost, high-performance video graphics cards such as those from Number Nine Visual Technology.
It was one of the best known graphics chips of the 1980s.

Details

The project was started in 1979, with trial production in 1980 and mass production starting in December of 1981. It was first used NEC  (known in North America as the NEC APC or "Advanced Personal Computer") in 1981. The N5200 sported a 5 MHz Intel 8086 processor on a 16-bit bus, and came with a text-only display board using this chip (in text mode). An optional graphics-only display board, sporting a second uPD7220 chip (operating in graphics mode), "merged" the text and graphics video through an XOR port (on each of the RGB signals) in HW. The only OS on the original NEC APC was the UCSD p-System, but later on (in 1982) CPM/86 support was added. In 1981, an English language paper written in 1980 by Tetsuji Oguchi, Misao Higuchi, Takashi Uno, Michiori Kamaya and Munekazu Suzuki was published in the IEEE. Nippon Electric Company (now 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 including Digital Equipment Corporation and Wang Laboratories.

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."
When the Apple Lisa was announced in 1983, the press raised questions on why the popular 7220 was not used.
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 manager Wayne 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 the vertical refresh cycle.

Variants
Variants included:
 Intel licensed the design and called it the 82720 graphics display controller. Announced in 1982, it was the first of what would become a long line of Intel graphics processing units. 
 East Germany (the German Democratic Republic) produced a replica designated U82720, used with the U880 replica of the Zilog Z80.
 The faster complementary metal–oxide–semiconductor (CMOS) variant was given the designation μPD72020.
A follow-on project produced the μPD72120 Advanced Graphics Display Controller (AGDC) which was faster and supported a 16-bit interface. It was named one of the "Top 100" products of 1987 by Electronics Design.

Internals
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 both registers; A1 for writing the command, A0 for writing the parameters to the queue.
The parts had an 8-bit data path.
Parts were available with clocks running from 4 MHz to 5.5 MHz, which was considered relatively high-performance for the time.

References

External links
 uPD7220/uPD7220A User Manual, December 1985
 Source code of driver for CP/M-86
 7220 and 72020 data sheets
  (in Japanese)

Graphics processing units
Graphics chips
muPD07220