370 Light Pen Diagnostic Program

This document describes the "370 Light Pen Diagnostic Program," a utility developed by C. Stein for DEC on April 29, 1964, to test the operation of the 370 Light Pen with a 340 Display on a PDP-4 computer.

The program's loading procedure involves placing a diagnostic tape in the reader and initiating it from a specified memory address. Console AC switches are used to select and configure the various tests and settings. All error detection for these diagnostics is visual.

The document details three primary tests:

1. Sensitivity and Resume IOT Test: This test checks the light pen's interrupt and display resume IOT functions across eight intensity levels. Horizontal vectors are drawn, and the light pen's ability to truncate them (indicating it "sees" light) and the display's ability to resume after an interrupt are verified.
2. Light Pen Follow Test: This diagnostic assesses the response speed of the 370 light pen. A cross is displayed in the center of the screen, and the operator moves the light pen over it, with two perpendicular lines drawn from the screen's center to the pen's current position.
3. Field of View Test: This test determines the light pen's "field of view" (the area it "sees") at different positions and intensities on the screen. A user-positioned and intensity-controlled box is displayed; when the pen is placed over it, a 4x enlargement and a digital readout of detected points appear.