KN220 CPU System Maintenance

This document serves as a maintenance and troubleshooting guide for the KN220 CPU system (used in the DECsystem 5500). It covers:

• System Overview: Describes the KN220 CPU and I/O modules, including the R3000 RISC processor, memory systems, and supported interfaces (DSSI, SCSI, Ethernet, and Q22-bus).
• Configuration: Provides guidelines for module ordering, memory configuration, and setting up DSSI and SCSI storage devices.
• Firmware: Details the KN220 diagnostic firmware, including boot procedures (ULTRIX-32 and MDM), console command usage (normal and maintenance modes), and environment variables.
• Troubleshooting and Diagnostics: Outlines ROM-based diagnostic tests, error message formats, system halt codes, and utility programs (such as the FE utility) for isolating hardware failures.
• Appendices: Include address space maps (for R3000 and CVAX), KFQSA adapter configuration, Prestoserve software data recovery procedures, a list of Field-Replaceable Units (FRUs), and related documentation references.