Small XY Display

This document, "PDP-X Technical Memorandum #8," dated July 11, 1967, describes a Small XY Display designed as a replacement for the 34 oscilloscope display commonly used with PDP-9 and PDP-8 computers. Authored by H. Burkhardt and L. Seligman, it outlines the display's capabilities, specifications, and programming interface.

The display controller is versatile, capable of driving Techtronix 503 or 564 oscilloscopes, Conrac type XY scopes, and future storage tubes. It supports graph plotting, character plotting, and non-complicated graphics. Key features include a "raster mode" for character generation and the ability to load or add data to individual 8-bit X and Y axis registers, providing a resolution of one part in 256. Four distinct intensity levels are available for highlighting data.

Programming the display involves manipulating a 2-byte status register using IOC/IOX (set/change) and IOS/IOT (sense/test) instructions. Data can be sent via IOW instructions or a multiplexor channel. The display operates in two primary modes: "Point Mode" (MODE=0) for individual X,Y coordinate plotting with variable intensity, and "Character Mode" (MODE=1) for plotting 8x2 point rasters from 2-byte data words, ignoring X/Y-Control bits and incrementing the X-axis by 2 after each raster. A full character typically uses an 8x6 raster, requiring 6 bytes of data. The status register bits control functions like interrupt enabling (ENABLE), interrupt address selection (LOW), device activity (BUSY), request for attention (REQ), and light pen interaction (LP ENABLE, LP HIT). X and Y control bits dictate how data bytes affect their respective registers (clear, load, unchanged, add). The document also provides programming examples for point plotting and character plotting with interrupt service routines.