DL11 Asynchronous Line Interface User's Manual

This document is the User's Manual for the DL11 Asynchronous Line Interface, published by Digital Equipment Corporation in September 1976 for the PDP-11 computer system.

Purpose: The DL11 is a character-buffered communications interface designed to translate serial bit stream data into parallel character data (and vice-versa) for transfer to or from the PDP-11 Unibus. It consists of a single integrated circuit quad module (M7800) containing independent receiver and transmitter units capable of simultaneous two-way communication.

Key Features and Options:

• Five Options: The DL11 is available in five options (DL11-A through DL11-E), each factory-configured for specific terminal types and communication requirements.

  • DL11-A and DL11-C: Primarily for Teletype control, using 20-mA current loops. The DL11-C offers more flexibility in data code and baud rate selection.
  • DL11-B and DL11-D: For EIA (Electronic Industries Association) terminal control, featuring EIA drivers and receivers. The DL11-D also provides greater flexibility.
  • DL11-E: Provides complete data set control for communication modems (e.g., Bell Model 103/202), handling handshaking signals.

• Data Formats: Options support either a "restricted" format (START bit, 8 DATA bits, 1 or 2 STOP bits) or "full selection" (START bit, 5-8 DATA bits, optional PARITY, and 1, 1.5, or 2 STOP bits). These formats are selected via jumpers on the module.

• Baud Rates: Baud rates depend on the installed crystal and a rotary switch setting, offering a range from 40 baud to 10K baud.

Installation and Configuration:

• The DL11 module can be mounted in a PDP-11 processor slot or a DD11-A Peripheral Mounting Panel.
• Configuration involves setting jumpers for specific data formats, addressing, and priority assignments. Baud rates are set by selecting a crystal and positioning a switch.
• Power connections are provided by the PDP-11 system, with an additional power module required for EIA options.
• Installation testing uses specific diagnostic programs supplied with the interface.

Functional Description:

• The DL11 manages serial-to-parallel conversion for incoming data and parallel-to-serial conversion for outgoing data.
• It includes logic for error detection (e.g., parity error, framing error, overrun error) and "break" generation (transmitting a continuous space).
• A "maintenance mode" allows for internal loopback testing of the interface circuits.

Programming Information:

• Device Registers: Software control is exercised through four dedicated device registers: Receiver Status Register (RCSR), Receiver Buffer Register (RBUF), Transmitter Status Register (XCSR), and Transmitter Buffer Register (XBUF).
• Interrupts: The DL11 generates Bus Request (BR) interrupts to signal events like a character being received (Receiver Done) or the transmitter being ready for a new character (Transmitter Ready). The DL11-E also supports interrupts for dataset events (e.g., RING, Carrier Detect).
• Addressing: Interrupt vector addresses are typically assigned using a floating vector convention for communications devices, though special fixed addresses are used for a console DL11-A or B.
• The manual provides details on timing considerations for efficient programming and notes on character formatting.