VT220

This technical manual is designed for field service engineers and trained personnel to assist in identifying and resolving malfunctions in the Digital Equipment Corporation VT220 Series terminal. It provides detailed functional descriptions of the terminal's major circuits and components.

The manual is structured into nine chapters covering:

• System Introduction: A general overview of the VT220 terminal, its physical description, display characteristics, communication environment, and operating modes (VT100, VT200 7-bit, VT200 8-bit, and VT52).
• Controls, Indicators, and Connectors: Descriptions of the monitor assembly, keyboard (LK201), visual indicators, audible indicators, and modem option.
• System Overview: An explanation of the VT220's system interactions during its three operating states: Set-Up, Local, and On-Line.
• CPU Logic: Details the central processing unit, its internal circuits, address latch, ROM, data buffer, screen RAM, attribute RAM, select decoder, keyboard interface, nonvolatile RAM (NVR), and configuration register.
• System Communication Logic: Covers the dual asynchronous receiver/transmitter (DUART), host data mux, printer interface, EIA host interface, and 20 mA interface.
• Video Logic: Describes the CRT controller, timing generator, blank circuits, character generator, attribute circuits, and video converter, all responsible for video output.
• Keyboard (LK201): A comprehensive look at the keyboard's operation, firmware functions, detailed circuit descriptions, communication, and programming.
• Monitor Circuits: Explains the video amplifier, horizontal and vertical deflection circuits, flyback transformer, dynamic focus, brightness control, and CRT device.
• Power Supply: Outlines the AC input components, AC conversion circuits, +12 V start-up circuit, input rectification, DC output circuits, overcurrent protection, pulse width modulator, DC OK circuit, and DC input components.

Additionally, the manual includes appendices that list the VT220 terminal's specifications, highlight differences between the VT220 and VT102 terminals, and provide register bit values for programming the VT220 Series terminal.