DMC11 IPL Synchronous Line Unit Maintenance Manual

This document is the DMC11 IPL synchronous line unit maintenance manual, a preliminary printing from May 1976 by Digital Equipment Corporation (DEC).

The manual provides comprehensive information for the installation, operation, and maintenance of the DMC11 Line Unit, a microprocessor-controlled device designed to interconnect PDP-11 computers in both local and remote network applications.

Key aspects of the document include:

• General Description and Specifications:

  • Covers four models of the line unit, supporting DDCMP (Digital Data Communications Message Protocol) and Bit Stuffing protocols. The controlling microprocessor primarily handles DDCMP.
  • DMC11-DA/FA (M8201) are remote units: They interface with external modems (EIA/CCITT V24 or V35) at speeds up to 19.2K bps (DA) or 56K bps (FA).
  • DMC11-MA/MD (M8202) are local units: They have built-in modems, operating over coaxial cable at speeds up to 1M bps (MA) or 56K bps (MD).
  • Common functions include parallel-to-serial data conversion, SYNC character detection, modem control, and Cyclic Redundancy Checking (CRC) for error detection (using CRC-16 for DDCMP and modified CRC-CCITT for Bit Stuffing).
  • Data buffering is handled by 64-word deep FIFO (First In/First Out) "silos" to manage speed differences between the microprocessor and line serialization.

• Installation:

  • Provides procedures for unpacking, inspection, and pre-installation setup, including detailed jumper and switch configurations specific to M8201 and M8202 models.
  • Outlines physical installation steps and initial checkout using diagnostic programs (MAINDEC-11-DZDME, DZDMF, DZDMG).
  • Includes specifications and installation guidelines for the local link coaxial cable (e.g., Belden 8232), covering physical characteristics, grounding, and considerations for attenuation and environmental factors.

• Programming and Detailed Description:

  • Explains the line unit's register structure (e.g., In/Out Data Silo, Control, Modem Control, Sync, Maintenance Registers) and their bit assignments for microprocessor interaction.
  • Provides an in-depth functional and circuit-level description of the line unit's logic, breaking it down into major sections such as the transmitter, receiver, CRC logic, data set interface (M8201 only), maintenance logic, initialization logic, and integral modem (M8202 only).

• Maintenance:

  • Outlines the philosophy for preventive and corrective maintenance.
  • Lists required test equipment and describes three distinct maintenance modes (Internal, System Test, External Maintenance) that utilize diagnostic programs and specific hardware setups for fault isolation.