RL11 Controller Technical Description Manual

This document is the RL11 Controller Technical Description Manual, published by Digital Equipment Corporation in April 1980.

It provides a detailed technical description of the RL11 Disk Controller, a hex-height module (M7762) designed for PDP-11 UNIBUS systems. The controller manages one to four RL01 or RL02 Disk Drives, which utilize removable disk cartridges with formatted capacities of 5.2 megabytes (RL01) or 10.4 megabytes (RL02).

Key aspects covered include:

• Subsystem Overview: The RL11 interfaces with the UNIBUS for CPU access and Direct Memory Access (DMA) data transfers, and with the disk drives via a proprietary I/O bus.
• User Information (Programming Interface): It details the eight primary functions the controller can perform (e.g., Read Data, Write Data, Seek, Get Status), accessible by the CPU through four addressable registers: Control Status Register (CSR), Bus Address Register (BAR), Disk Address Register (DAR), and Multipurpose Register (MPR). It also notes limitations like the absence of implied or spiral seeks, requiring software intervention for multi-track operations.
• Interface Level Description: A technical breakdown of how the RL11 interacts with both the UNIBUS (as a slave for CPU access and as a master for interrupts and DMA) and the drive I/O bus (including signal definitions and physical cabling).
• Functional Description (Internal Logic): Explanations of the controller's internal components and their functions, such as the silo buffer (for data staging), CRC generator/checker, write data encode/precompensation logic, system clock, phase-locked loop and data separator, and the crucial role of two Read-Only Memories (Function Control ROM and Format Control ROM) in coordinating all operations.
• Command Descriptions: Detailed step-by-step explanations of how each of the eight commands is executed by the controller's internal logic and ROMs.

The manual is intended to aid in understanding the controller's functionality at a component level, assuming basic knowledge of PDP-11 processors, the UNIBUS, and disk principles.