The Omnibus Interface

This document provides a technical overview of the "OMNIBUS" interface system used for the PDP-8/E computer. It serves as a guide for designers building custom interface modules.

Key highlights include:

• System Architecture: The OMNIBUS is an etched backplane board with standardized connector pin assignments, which eliminates random wiring, increases circuit density, and allows modules to be placed in any available slot.
• Expansion: The system supports high-density packaging and can be expanded using an OMNIBUS expansion unit to accommodate additional modules.
• Integration: The document details the relationship between the PDP-8/E, the OMNIBUS, and external buses. It explains that standard peripherals use DEC-supplied modules, while custom requirements can be met by designing specific interface modules that adhere to the established OMNIBUS signal protocols.
• Technical Specifications: The text includes detailed information on bus structure, logic voltage levels, signal definitions (such as MDO-11, I/O PAUSE, and C-lines), and loading rules. It also provides diagrams for bus configuration, pin assignments, and electrical load circuits to assist engineers in creating functional, reliable interfaces.