LP20 Line Printer System Manual

This document serves as a comprehensive system manual for the LP20 Line Printer System, detailing its description, installation, operation, programming, theory, and maintenance. The LP20 system is a hard-copy printer designed to interface with the PDP-11 Unibus, consisting of a line printer and a separate solid-state LP20 Controller.

Key features and operational aspects include:

• Direct Memory Access (DMA): The system is designed to print large amounts of text with minimal software intervention by transferring characters via DMA.
• Controller Functionality: The LP20 Controller utilizes a 256-word, 13-bit Random Access Memory (RAM) to control character-dependent operations like code conversion, horizontal tabulation (every 8 spaces), and automatic line overflow (after 132 characters). It also flags errors and special character conditions to the processor via bus interrupts.
• Vertical Format Unit (VFU): Most printers supported by the LP20 Controller use a programmable Direct Access Vertical Format Unit (DAVFU) for vertical forms control, while some (LP10-J, K models) use a paper tape VFU. The DAVFU is loaded via DMA and has 12 user-definable channels.

• Operational Modes: The controller operates in four primary modes:

  1. RAM Load Mode: Used to load the translation RAM from main memory, defining character behaviors.
  2. DAVFU Load Mode: Used to load the DAVFU for vertical formatting from main memory.
  3. Print Mode: The standard operational mode for printing data, utilizing the loaded RAM and DAVFU configurations.
  4. Test Mode: Simulates print mode without physical output, primarily for diagnostic purposes.

• Data Integrity: The system incorporates RAM parity checking and data transfer checksum computation to ensure data integrity.

• Installation and Maintenance: The manual provides detailed procedures for unpacking, inspecting, configuring (addressing, priority levels, VFU type), and cabling the LP20 Controller and associated line printers. Preventive maintenance is minimal, focusing on cable inspection and running diagnostic programs.
• Supported Printers: The LP20 Controller supports various line printer models, including LP05, LP07, LP10, and LP14, offering different print speeds (e.g., 230-1250 lines/minute) and character sets (64 or 96 ASCII). All supported line printers are plug-for-plug compatible with identical cabling.