DMC11 IPL Synchronous Line Unit User's Manual

This document is a user's manual for the DMC11 IPL synchronous line unit for PDP-11 computers, published by Digital Equipment Corporation in September 1976.

The manual provides comprehensive information for the installation, operation, and programming of the DMC11 Line Unit, which is designed to interconnect PDP-11 computers in both local and remote network applications.

Key aspects covered include:

1. General Description:

   • The DMC11 Network Link consists of a synchronous line unit controlled by a microprocessor (specifically, the DMC11-AD M8200 microprocessor is required for its function).
   • It supports two main protocols: Digital Data Communications Message Protocol (DDCMP) for 8-bit byte-oriented operation and Bit Stuff Mode for bit-oriented message protocols using flag and abort sequences.
   • Four models of the line unit are detailed:
     • Remote (M8201): DMC11-DA (EIA/CCITT V24, up to 19.2K bps) and DMC11-FA (CCITT V35, up to 56K bps), both with modem control and level conversion logic.
     • Local (M8202): DMC11-MA (1M bps) and DMC11-MD (56K bps), both with built-in modems for coaxial cable connections.
   • It performs standard communication functions like parallel-to-serial/serial-to-parallel conversion, SYNC character detection, modem control, Cyclic Redundancy Character (CRC) testing, and automatic bit/flag/abort sequence handling.
   • Data transfer between the microprocessor and line unit occurs via 64-word deep First In/First Out (FIFO) data silos (Out Data Silo for transmit, In Data Silo for receive) to manage speed differences.

2. Installation:

   • Detailed procedures for unpacking, inspection, and pre-installation setup, including a critical note about the prerequisite installation of the DMC11-AD Microprocessor (M8200).
   • Extensive instructions on checking and configuring jumpers (W1-W6) and DIP switches (Switch Packs No. 1, 2, and 3) that control various functionalities like CRC behavior, modem signals, interface compatibility (V24/V35), and enabling features for down-line loading.
   • Guidance on physical installation of the hex modules into PDP-11 Unibus end slots and connecting interconnect/modem/coaxial cables.
   • Information on selecting, installing, and maintaining the local link cable (recommending Belden 8232 double-shielded triaxial cable), including electrical characteristics, environmental factors, and critical grounding procedures (with warnings against improper connections).
   • Discussion of full-duplex (two-cable) and half-duplex (single-cable) operation modes and their hardware considerations.

3. Programming:

   • Overview of the nine 8-bit registers used for control and data transfer, including their addresses and read/write capabilities (e.g., In/Out Data Silo, Out/In Control, Modem Control, Sync, Maintenance Registers).
   • Detailed explanations of register bit assignments and their functions, such as TSOM (Transmit Start of Message) and TEOM (Transmit End of Message) for output, and BCC MATCH (Block Check Character Match) and BLOCK END for input.
   • Emphasis on specific programming procedures, such as the critical order of reading In Control registers before the In Data Silo to avoid losing status information.

In essence, the manual serves as a complete technical guide for setting up and utilizing the DMC11 Line Unit to establish synchronous data communication links between PDP-11 systems.