Nec D7220D: what it is

The NEC D7220D is a graphics display controller (gdc), i.e., a video coprocessor (1980s era) that handles bitmapped graphics and character mode, reducing CPU load for drawing operations (pixel plotting, lines, arcs, circles, and text handling via character generation/management depending on the implementation).

What it does in practice

• It belongs to the NEC μpd7220 family (“NEC 7220”), one of the most widely used LSI graphics controllers of its time.

• It typically works with external video memory and provides hardware functions useful for screen updates and buffer operations (e.g., read-modify-write), depending on the board/design where it is integrated.

• It was used in various vintage platforms and graphics boards; an Intel variant/license also exists (often referred to as the 82720), with compatibility to be verified case by case (timing, clock, bus).

Quick identification

• Markings such as D7220D-1 usually indicate a speed grade or revision: for replacements, matching the exact variant matters.

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See:   Graphic Display Controller

Specifications

The D7220D graphic chip in NMOS technology, was mounted on several DEC stations, including the DEC Rainbow 100, NCR DMV.

Fearures :

Microprocessor Interface

• DMA transfer with 8257 or 8237 controllers
• FIFO Command Buffering

Dispaly Memory Interface :

• Up to 256k words of 16 bits
• Read-Modify-Write (RMW) Display ;emory cicles in under 800ns
• Dynamic RAM refresh cycles for nonaccessed memory

Light Pen Input

External video syncronization mode

Graphics mode

• Four megabit, bit- mapped display memory

Character mode

• 8k character code and attribute display memory

Mixed Graphics and Character Mode

• 64k if all characters
• 1 megapixel if all graphics

Graphics Capabilities

• Figure drawing of lines, arc/circles, rectangles and graphics characters in 800ns per pixel
• Display 1024 by 1024 pixels with 4 planes of color or grayscale
• Two independently scrollable areas

Character Capabilities

• Auto cursor advance
• Four independently scrollable areas
• Programmable cursor height
• Characters per row : up to 256
• Characters row per screen : up to 100

Video Display format

• Zoom magnification factors of 1 to 16
• Panning
• Command settable video raster parameters

Technology

• Single +5v NMOS 40-in DIP

DMA Capability

• Bytes or word transfers
• 4 clock periods per byte transferred