VT48 Display Processor Unit

This document details the VT48 Display Processor Unit (DPU), a high-speed, interactive graphics processor and a key component of the VS60 Vectoring System. It is designed to drive the VR48 Table and Scope Assembly display monitor, receiving 16-bit instructions from a host PDP-II processor.

The VT48 operates with its own Display Program Counter (DPC) and executes 25 instructions, divided into Load Status, Graphic Entity, and Branch categories. Load Status instructions configure internal settings (like interrupts, scale factors, and name values). Ten types of Graphic Entity instructions generate and refresh visual elements such as points, vectors, and characters. Branch instructions manage program flow, including subroutine calls, leveraging an 8-level stack memory for nesting and context storage.

The DPU incorporates 16 addressable registers for instruction processing and status information. It utilizes silo memory to store control and status data, and a graphics calculation logic for complex arithmetic operations, including vector scissoring, scaling, offset calculations, and light pen hit detection. The graphics calculation logic, along with the dedicated vector and character generators, functions asynchronously to efficiently create intricate displays and text.

Key specifications include refresh rates of 30 or 40 frames per second, 8 programmable intensity levels, 4 line types, hardware blinking, and flexible scaling for both vectors (1/4 to 3-3/4 normal size) and characters (1/2 to 2 normal size). It supports a 12x12 bit virtual display area, with analog stroke generation for vectors (e.g., 26µs for full screen) and directed analog strokes for characters (Full ASCII, rotatable), with an average writing time of 9µs per character.