UDA50

This document is the User Guide for the UDA50 Disk Controller, first published in May 1983 with a second edition in July 1984 by Digital Equipment Corporation. The UDA50 is an intelligent controller designed to interface up to four 16-bit RA series disk drives with any UNIBUS system, using a radial bus configuration rather than a daisy-chain.

The controller is part of Digital's Storage Architecture (DSA) family and implements the Mass Storage Control Protocol (MSCP). This means the controller manages I/O, presents the disk subsystem as logical blocks (512 bytes each) without exposing disk geometry to the host, and handles error recovery and data movement independently of the host.

The UDA50 consists of two hex-height modules: the SDI (Standard Disk Interconnect) module (M7486) and the Processor module (M7485). The SDI module handles communication with disk drives, contains a 32KB high-speed buffer, converts data formats, and generates Real-time Error Correction Code (ECC). The Processor module controls UNIBUS interaction via two registers (IP and SA at octal addresses 772150 and 772152, respectively), manages interrupt vectors, reports microcode errors, and contains a dual microprocessor for efficient execution of two independent microprograms.

The UDA50's functional microcode is divided into two streams: the UNIBUS Control Stream (controller-to-host interface) and the Drive Control Stream (controller-to-disk interface). These streams manage packet exchange, command processing, data transfer, error correction, initialization, and disk drive operations.

The guide outlines detailed installation procedures, including setting UNIBUS address switches and jumpers, UNIBUS tuning (such as NPR priority jumper settings), module insertion, flat ribbon cable and SDI cable installation, and I/O bulkhead connector mounting. It also specifies the required bootstrap ROMs for PDP-11 and VAX 11/750 systems.

A significant section covers the Field Acceptance Test Procedure, which involves running UDA50-resident diagnostics (indicated by cycling LEDs on modules), disk drive-resident diagnostics, and UDA50 host-resident diagnostics (CZUDC for PDP-11 and ZZ-EVRLA/ZZ-EVRLC for VAX systems). Error codes for non-cycling LEDs are provided for troubleshooting.

Finally, the document includes programmer information, detailing specific UDA50 programming aspects such as register addresses, interrupt vector settings, command limits, NPR burst values, supported disk formats (512 bytes), and diagnostic protocols (MSCP and DUP).