PDP-11/20 system manual

This manual serves as a comprehensive guide for the PDP-11/20 System, detailing its theory of operation, maintenance, and user procedures. It's part of a series of modular manuals, each focusing on a specific system component, and assumes a basic understanding of digital computer theory.

The PDP-11/20 is a 16-bit general-purpose computer utilizing a high-speed Unibus for all communication between its major components:

• KA11 Processor: The central processing unit, featuring eight hardware registers (for accumulation, indexing, and stack management) and a full instruction set supporting byte operations and reentrant code. It handles instruction decoding, data modification, and Unibus allocation, with standard power fail/restart.
• KY11-A Programmer's Console: The primary user interface, allowing manual control over program execution (start, stop, load, modify, continue, single-step) and displaying system status (data, address, major machine states).
• MM11-E Core Memory: A random-access read/write memory with a 1.2 µs cycle time, storing 4K 16-bit words (expandable). It operates as a slave device on the Unibus.
• KL11 Teletype Control: An interface between the electromechanical Teletype unit and the Unibus, handling serial-to-parallel data conversion and priority interrupts.
• H720 Power Supply: Provides regulated power for the system and includes protection circuits.
• BA11 Mounting Box: The physical enclosure for the system components.

The manual describes system operation through its controls and indicators, explaining how the console switches and Teletype controls interact with the system and how the various display lights reflect the processor's state and data flow.

Operating procedures cover essential tasks such as:

• Manual Loading: Entering the bootstrap loader into core memory via console switches.
• Automatic Loading: Using the bootstrap loader to load an absolute loader, which then loads other binary programs from paper tape.
• Running Programs: Executing loaded programs and manually stopping/restarting them.
• Manual Operation: Step-by-step program debugging using single-instruction or single-bus-cycle modes.
• Teletype Operation: Procedures for both off-line functions (typing, punching, reading, duplicating tapes) and on-line interaction with the computer.