DL11 Asynchronous Line Interface Manual

This document is the DL11 Asynchronous Line Interface Manual for the PDP-11 computer, published by Digital Equipment Corporation (DEC).

Purpose: The DL11 is a character-buffered communications interface designed to convert serial data from external communication devices into parallel data for the PDP-11 Unibus, and vice-versa. It features independent receiver and transmitter units, enabling simultaneous two-way communication. It also provides status and control bits for program-controlled operations, monitoring, and interrupt functions.

Key Information and Features:

• Options (DL11-A through DL11-E): The manual describes five distinct options, each tailored for different communication needs:

  • DL11-A/C: Primarily for Teletype control, using a 20-mA current loop. The DL11-C offers more flexible data code and baud rate selection.
  • DL11-B/D: Designed for EIA (Electronic Industries Association) terminal control (e.g., display terminals), with EIA drivers and receivers. The DL11-D offers more flexibility.
  • DL11-E: Provides comprehensive data set (modem) control, enabling monitoring of modem signals (e.g., RING, CARRIER DETECT, CLEAR TO SEND) and program control over transmission signals (e.g., REQUEST TO SEND, DATA TERMINAL READY).

• Data Formats: Supports "restricted" (DL11-A/B: START, 8 DATA, 1 or 2 STOP bits) and "full selection" (DL11-C/D/E: START, 5-8 DATA, optional PARITY, 1, 1.5, or 2 STOP bits) formats, configurable via jumpers on the module.

• Baud Rates: Selectable via rotary switches and internal crystal oscillators (or external clocks), offering various speeds (e.g., 110, 150, 300, 600, 1200, 2400 baud).
• Physical Design: The DL11 interface is a single M7800 Quad Integrated Circuit Module that plugs into PDP-11 Unibus slots.
• Device Registers: Operates through four key registers (Receiver Status Register, Receiver Buffer Register, Transmitter Status Register, Transmitter Buffer Register) for software control, data transfer, and status monitoring.
• Interrupts: Supports vectored BR interrupts for both receiver and transmitter events. The DL11-E option includes additional dataset-specific interrupt sources.
• Maintenance Mode: Allows for closed-loop testing by connecting the transmitter output to the receiver input, forcing the receiver to run at the transmitter's speed.
• Break Generation Logic: DL11-C, D, and E options can transmit a continuous "space" signal (break).
• UART (Universal Asynchronous Receiver/Transmitter): The core component that performs the serial-to-parallel and parallel-to-serial data conversion, including error detection and configurable parameters like parity and stop bits. The UART is double-buffered.

Manual Structure: The document is organized into five main chapters covering Introduction, General Description, Installation and Configuration, Programming Information, and Detailed Description. It also includes appendices with IC schematics and detailed information on interrupt vector addressing. The manual is intended for users familiar with basic digital computer theory.