PDP-7

This document serves as a comprehensive maintenance manual for the PDP-7, a general-purpose, solid-state, 18-bit word length computer. It provides detailed operational and maintenance information for engineers and technicians familiar with digital logic and computer programming.

The PDP-7 system is composed of a central processor, core memory, and input/output (I/O) devices. The processor executes arithmetic and logical operations based on a varied instruction repertoire (memory reference, augmented, EAE, IOT, OPR) and operates through key control states: fetch, defer, execute, and break, all precisely timed. Manual interaction is facilitated by an operator console featuring controls like START, STOP, EXAMINE, DEPOSIT, and READ-IN, complemented by an indicator panel and dedicated controls for the Teletype and paper tape reader. Programmed operations can be interrupted or modified by program, data, or clock breaks.

The core memory, with a standard capacity of 4096 or 8192 words (expandable to 32,768), features a 1.75 µsec cycle time. Its architecture and circuit functions, including memory selectors, inhibit drivers, and sense amplifiers, are described in detail. The I/O interface manages data flow and device selection, incorporating components like device selectors, information collectors, and distributors. Standard peripheral equipment includes a Teletype Model 33 KSR unit, a paper tape reader (Type 444B), and a tape punch (Type 75D).

The manual extensively covers optional equipment, such as the Extended Arithmetic Element (EAE) Type 177 for accelerated arithmetic (multiplication, division, shifts), the Automatic Priority Interrupt (API) Type 172B for prioritized I/O device management, and the Data Interrupt Multiplexer Type 173 for high-speed data transfers with multiple devices. Memory expansion and parity options are also detailed.

Maintenance strategies emphasize module replacement to minimize downtime. This includes preventive maintenance, such as mechanical and power supply checks, and marginal checks utilizing diagnostic programs. Corrective maintenance procedures guide users through system troubleshooting, signal tracing, and aggravation tests for intermittent faults, leading to circuit-level problem isolation and repair. The document concludes with a section on engineering drawings, outlining their conventions and symbols for in-depth system analysis.