Octobus Interface Documentation

This folder contains documentation for the Norsk Data Octobus communication interface used for ND-100/ND-500 inter-processor communication.

Contents

File	Description
OCTOBUS-PROTOCOL-REFERENCE.md	Complete protocol reference including register layout, command codes, message structure, and transmission mechanisms
octobus_protocol_frame_format_and_introduction.md	Frame format and protocol introduction

Overview

The Octobus is a high-speed serial interface used to connect the ND-100 control processor with ND-500 computation processors (SAMSON). It uses dual 4-register controllers:

• Input Controller (Base 100400): Receives data from Octobus
• Output Controller (Base 100404): Transmits data to Octobus

Key Features

• 16-bit frame-based communication
• Interrupt-driven with ident codes 40 (input) and 41 (output)
• Support for single-frame and multi-byte messages
• "Kick" mechanism for CPU signaling
• Loopback mode for diagnostics

Related Documentation

• ../../ND5000/README.md - ND-5000/SAMSON documentation index (master protocol reference, OMD-0 test protocol RE, microcode catalog, emulation handoff). The ND5000 folder holds the newest, evidence-marked material - read its index for the recommended order.
• ../../ND500/README.md - ND-500 processor documentation (the old link pointed at Devices\ND500 which does not exist)
• ../../ND500/ND500-BUS-OCTOBUS-HW-INTERFACE.md - ND-500 side + MON 60 subfunction table
• ../../OS/06-MULTIPORT-MEMORY-AND-ND500-COMMUNICATION.md - 5MPM shared memory
• ../../NPL-SOURCE/NPL/MP-P2-N500.NPL - ND-500 monitor routines
• ../../NPL-SOURCE/NPL/PH-P2-OPPSTART.NPL - Octobus initialization (OCSTART)

Source References

The documentation in this folder is derived from analysis of: - PH-P2-OPPSTART.NPL - Octobus startup routines - MP-P2-N500.NPL - ND-500 monitor routines including XKICK500, XRS5CPU, 5OMBREAD - CC-P2-N500.NPL - ND-500 command processing - N500-SYMBOLS.SYMB.TXT - Symbol definitions for command codes

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Last Updated: 2026-07-16