DH11 Asynchronous 16-line Multiplexer Maintenance Manual

This document is a Maintenance Manual for the Digital Equipment Corporation (DEC) DH11 Asynchronous 16-Line Programmable Multiplexer. It provides comprehensive information for the installation, operation, programming, and detailed hardware description, as well as extensive maintenance and troubleshooting procedures for the DH11.

Key aspects summarized in the manual include:

1. General Description:

   • Function: The DH11 connects a PDP-11 processor to 16 asynchronous serial communication lines, with individually programmable parameters for each line.
   • Programmable Parameters: These include character length (5, 6, 7, or 8 bits), number of stop bits (1, 1.5, or 2), parity (odd, even, or none), half or full duplex operating mode, and various baud rates (from 0 to 9600 Baud, plus external inputs).
   • Data Handling: It uses 16 double-buffered MOS/LSI receivers to assemble incoming characters, which are then stored in a 64-word deep First-In, First-Out (FIFO) buffer called the "silo." Transmitters utilize direct memory transfers (NPR) from PDP-11 memory.
   • Auto-Echo: A hardware feature allows received characters to be echoed back without software intervention, unless errors like framing or overrun are detected.
   • Interrupts: Supports receiver interrupts (silo alarm, storage overflow) and transmitter interrupts (transmission complete, non-existent memory access).
   • Scalability: Up to 16 DH11 units can be connected to a single PDP-11, supporting a total of 256 lines.
   • Physical Variants: Describes different DH11-AA, -AB, -AC, -AD, and -AE configurations, detailing their line interfaces (e.g., 20 mA current loops, EIA/CCITT, telegraph lines) and associated distribution panels and power supplies.

2. Installation: Provides step-by-step instructions for unpacking, verifying components, installing modules into specific slots (highlighting floating addresses and priority plugs), and initial power-on checks. Crucial warnings about proper cable interconnections are included.

3. Programming: Details the bit assignments and functions of the DH11's eight registers (System Control, Next Received Character, Line Parameter, Current Address, Byte Count, Buffer Active, Break Control, and Silo Status Registers). It explains how to programmatically control line parameters, initiate transmissions, manage received data, and handle interrupts.

4. Detailed Hardware Description: Offers in-depth explanations of the internal logic, including:

   • Address Selector and Gating Control: How the DH11 decodes Unibus addresses and generates control signals for its registers.
   • Clock Module (M4540): Generates the various Baud rates using a crystal oscillator and a series of counters.
   • Line Parameter Control Module (M7288): Handles the selection of line-specific operational parameters.
   • Transmitter and Receiver Scanners: Manages the sequential processing of lines for transmission and reception.
   • Current Address Register (CAR) and Byte Count Register (BCR): Manages direct memory transfers for data transmission, including loading and incrementing memory addresses and byte counts.
   • FIFO Buffer (Silo): Describes the architecture and operation of the character buffer.
   • M7280 Multiple UART Card: Contains Universal Asynchronous Receiver Transmitters (UARTs) responsible for serial-to-parallel and parallel-to-serial data conversion.
   • Bus Transactions: Explains how the DH11 interacts with the PDP-11 Unibus (DATI, DATO, DATOB, and Interrupt transactions).

5. Maintenance:

   • Diagnostic Tests: Provides a summary and detailed instructions for running various diagnostic programs (MAINDECs DZDHA through DZDHK) to test static logic, memory, basic logic, speed selection, character length, single-line/multi-line data transfer, auto-echo, break/half-duplex, and echo functions.
   • Troubleshooting: Offers a comprehensive failure analysis section, guiding technicians to diagnose problems based on specific error messages, inspect circuit board components and pin signals with an oscilloscope, and verify expected waveforms.

The manual is designed to equip users with the necessary information to install, operate, program, and maintain the DH11 asynchronous multiplexer, ensuring its proper functioning within a PDP-11 system.