Rainbow Color/Graphics Option

This document serves as a programmer's reference guide for the Digital Equipment Corporation Rainbow Color/Graphics Option. It is targeted at experienced systems programmers with knowledge of graphics and 8088 programming, focusing on applications for Rainbow video monitors.

The guide details the hardware components, including the NEC uPD7220 Graphics Display Controller (GDC), an 8x64K dynamic RAM video memory (bitmap), a Write Buffer, Pattern Generator, Scroll Map, ALU/PS Register, Color Map, and Readback hardware. It outlines two resolution modes: Medium Resolution (384x240 pixels, up to 16 colors/shades) and High Resolution (800x240 pixels, up to 4 colors/shades), and four operational modes: Word, Vector, Scroll, and Readback. Supported monitor configurations (monochrome, color, or dual) are also described.

Programming guidelines cover initialization and control of the graphics option and GDC, setup for various bitmap write operations (area, vector, text), read operations, and vertical/horizontal scrolling. The document concludes with comprehensive reference material on the option's registers, buffers, and maps, as well as a list of GDC commands, hardware specifications, and a block diagram.