DU11 Single Line Programmable Synchronous Interface Maintenance Manual

This document is the DU11 single line programmable synchronous interface maintenance manual for Digital Equipment Corporation (DEC) PDP-11 computers, published in 1973-1974.

The DU11 is a hardware interface designed to establish a single-line data communication channel between a PDP-11 computer (a parallel I/O device) and a modem (a serial I/O device), compatible with Bell 201 and Bell 303 modems. It performs essential functions such as serial-to-parallel and parallel-to-serial data conversion, EIA to TTL voltage level conversion, and modem control.

Key aspects of the DU11 covered in the manual include:

• Operation Modes: It supports synchronous and isochronous serial data transmission, operating in half or full duplex, with configurable character lengths (5-8 bits plus parity).
• Models: Two versions are detailed: DU11-DA (for synchronous Bell 201 modems) and DU11-EA (for current mode Bell 303 modems).
• Performance: Capable of speeds up to 10K baud (EIA/CCITT) and 100K baud (current mode), though it notes that program response time may become a limiting factor at higher rates.
• Control and Programming: The interface is entirely program-controlled through five dedicated device registers (RXCSR, RXDBUF, PARCSR, TXCSR, TXDBUF), which manage receiver/transmitter status, data buffering, and overall operational parameters. It generates interrupt requests for various communication events.
• Installation: Detailed instructions cover mounting the module in PDP-11 systems, connecting modem cables, and configuring Unibus and interrupt vector addresses using rocker switches and jumpers.
• Maintenance: The manual provides a comprehensive guide for preventive and corrective maintenance, outlining required test equipment, diagnostic programs, and specific maintenance modes (System Test, Internal Loop, External Loop) for troubleshooting.

In essence, the document serves as a complete technical reference for understanding, installing, programming, and maintaining the DU11 interface for PDP-11 data communication systems.