RM Massbus Adapter Technical Description Manual

This technical description manual, "RM MASSBUS ADAPTER TECHNICAL DESCRIPTION MANUAL (EK-RMADA-TD-001)," published in October 1980 by Digital Equipment Corporation, details the RM adapter and its operation within disk subsystems.

The RM adapter is an electronic assembly designed to interface MASSBUS controllers with disk drive units. Its primary functions include:

• Converting controller command requests into drive command sequences.
• Establishing single-port or dual-port operation.
• Monitoring and reporting drive status to the controller.

Physically, the adapter consists of an integrated backplane, card cage, various plug-in circuit modules (up to eight, of six different types), and a power supply. It supports both single-port (one controller) and dual-port (two controllers) configurations, allowing shared access to disk drives.

The document describes two main interfaces:

1. MASSBUS Interface: Connects the RH controller to the RM adapter, comprising bidirectional data bus lines (18-bit plus parity) and control bus lines (16-bit plus parity) that handle command, status, and timing signals (e.g., RUN, OCCUPIED, DEMAND, ATTENTION). It also details the function of 16 adapter registers for various control and status parameters.
2. Drive Interface (Cables A and B): Connects the RM adapter to the disk drive, transmitting addressing, status (e.g., UNIT READY, FAULT), timing (e.g., SECTOR PULSE, INDEX Pulse), and data signals. A power sequence cable prevents simultaneous startup of multiple drives.

Internally, the RM adapter's operations are managed by specific circuit modules like the control interface (for handshaking and registers), data sequencer (for data flow, ECC, and CRC), control sequencer (for command execution), and drive interface. It utilizes Programmable Logic Arrays (PLAs) for signal testing and error decoding. Command execution is categorized into "Command Immediate" (simple resets), "Command Immediate with ATA Execution" (mechanical motions like seek and recalibrate), and "Data Transfer Commands" (read/write operations), each with detailed sequencing logic.

The manual concludes by outlining the necessary hardware and software modifications (e.g., jumper connections, specific data sequencer modules, register bit assignments) required to make the RM adapter compatible with various disk drive models (e.g., RM02, RM03, RM05, RM80), accounting for differences in storage capacity, spindle speed, and special features.