VAX-11/780 KC780 Console Interface Technical Description

This document provides a comprehensive technical description of the KC780 Console Interface Board (CIB) for the VAX-11/780 computer system.

The CIB serves as the critical link between the VAX-11/780 Central Processor Unit (CPU) and the console subsystem, which includes an LSI-11 microprocessor, a terminal, and a floppy disk. It integrates three main buses: the Q bus (LSI-11 bus) for communication with the console components, the ID (Internal Data) bus for high-speed data transfer within the VAX-11/780 CPU, and the V bus for diagnostic monitoring of VAX CPU test points.

The CIB enables a wide range of console functions, including:

• Traditional Console Operations: Such as EXAMINE, DEPOSIT, HALT, and START.
• Diagnostic and Maintenance Functions: Like loading microcode, controlling execution, monitoring results, and single-stepping the clock.
• I/O Register Materialization: Making terminal and floppy disk I/O registers accessible to both the LSI-11 (via the Q bus) and the VAX-11/780 CPU (via the ID bus).

The LSI-11 operates in two primary modes: Program I/O mode, where it acts as a character handler for the VAX-11/780's operator terminal, and Console I/O mode, where it interprets commands for system control and maintenance.

Interaction between the LSI-11 and the VAX-11/780 CPU, facilitated by the CIB's various registers (e.g., Console Control/Status, Machine Control, Miscellaneous Control/Status, TO ID, FM ID), depends on the VAX CPU's state (running or halted) and the LSI-11's operating mode. When the VAX-11/780 is running, communication occurs via interrupt-driven transfers through specific data registers. When halted, the LSI-11 gains more direct control over the VAX-11/780's internal operations and can directly reference ID bus registers for detailed diagnostics.

The document also delves into the detailed logic and timing of the CIB's interfaces, address decoding, and transfer synchronization mechanisms to explain its hardware implementation.