Instruction Manual

This document is an Instruction Manual for the Digital Equipment Corporation (DEC) Type 34H Oscilloscope Display, designed for use with the PDP-9 computer system. The Type 34H is a two-axis digital-to-analog converter and intensifying circuit that enables the PDP-9 to display points on a Cathode Ray Tube (CRT) screen.

The manual covers:

• Installation: It details the physical mounting of the oscilloscope in a standard 19-inch rack adjacent to the central processor and the location of the display logic modules within the processor rack, noting that the display logic draws power from the basic PDP-9 system.
• Programming: It lists the specific IOT (In-Out Transfer) commands used to control the 34H Display, including functions for clearing/loading x and y-coordinate buffers, displaying points, and setting brightness levels. Programming examples demonstrate how to generate basic graphical elements like vertical, horizontal, and diagonal lines.
• Theory of Operation: This section explains the internal workings of the 34H Display, which comprises x-axis (XB) and y-axis (YB) buffers, a brightness register (BR), and an IOT decoder. Points are positioned on a 1024x1024 array using 10-bit coordinate data converted to analog deflection signals. Point intensity is controlled by a 2-bit brightness register, offering four levels from "no display" to "brightest." The display can plot points at approximately 30 kHz (10 µs per point). It also describes the logic control, processor turn-on sequences, IOT command generation, and how the optional light pen operates by sensing displayed points and triggering program interrupt or Automatic Priority Interrupt (API) requests for computer interaction.
• Maintenance: It outlines preventive maintenance procedures (referencing the PDP-9 Maintenance Manual), power supply and margin checks, and refers to the oscilloscope manufacturer's documentation for scope-specific maintenance. A dedicated diagnostic program (MAINDEC-9A-D6AB-D) is provided for calibrating, checking out, and diagnosing issues with the display and light pen. The section concludes with lists of relevant engineering drawings and the electronic modules used in the 34H Display.
• Glossary of Terms: A list of definitions for technical terms used throughout the manual.