Dec-Tape Control Type 551

Summary

This document is the technical maintenance and operations manual for the Digital Equipment Corporation (DEC) DECtape Control Type 551. This hardware is designed to operate up to four Type 555 Dual Tape Transports, managing the transfer of binary data between magnetic tape and a PDP-6 Arithmetic Processor.

The manual is organized into the following key sections:

• System Description: Details the physical specifications and the functional role of the Type 551 control, including the recording format (Manchester recording on a 5-channel 10-track system), block formats, interblock zones, and the various hardware registers (Control, Status, Read-Write Buffer, etc.) used to manage tape operations.
• Theory of Operation: Provides an in-depth explanation of how the control manages tape motion, command decoding, error checking, and data flow. It covers both reading and writing operations, including special modes for writing timing and mark tracks.
• Interface: Lists the specific input and output signals between the DECtape control and the I/O bus, the Type 555 Tape Transports, and the Data Control Type 136.
• Maintenance: Outlines preventive and corrective maintenance procedures, including mechanical checks, power supply verification, and troubleshooting techniques for modules, circuits, and components.
• Engineering Drawings: Includes an appendix that explains the coordinate system and logic symbols used in the system’s block and circuit schematics.