550 miscDocs

This document describes the DIGITAL COMPUTER OPTION 550 Micro-Magnetic Tape Control system, detailing its operation, programming interfaces, and associated utility programs, along with various technical troubleshooting tips.

Key aspects include:

1. System Overview: The Type 550 Control manages data transfer for up to four Type 555 dual tape transports (8 drives) with PDP-4 or PDP-1 computers. It handles data word by word or in blocks, performing assembly and disassembly between 3-bit tape lines and 18-bit computer words. Exact tape addressing is enabled by a serially coded Mark Track.
2. Operational Flow: The control signals the computer via flags: an interrupt flag indicates a word is available during reading, and a flag requests a new word during writing. Block ends are indicated by a separate flag, and an error flag signals issues like "off end of tape" or "program too slow." Error detection primarily relies on a programmed checksum, with standard block lengths being 256 words plus two checksum words.
3. Commands and Timing: The system has defined start (0.1 sec) and reverse (0.4 sec) delays. PDP-4 instructions include Read, Write, Load Control, Select (units), Read Status, and various flag-skipping commands (Data, Block, Error).
4. Programmer Interface: Data, Block End, and Error flags are crucial for programmers to manage data flow and respond to system states. Specific timing requirements exist for commands in different modes (Search, Read, Write, Move) to ensure reliable operation due to relay operate times.
5. Hardware Components: The control includes an 18-bit Read/Write serial-parallel buffer, an 18-bit In/Out buffer for parallel transfer to the main machine, and a 7-bit Mark Track recognition register. Program interrupts occur for each 18-bit data word transfer (every 200 microseconds) and for block marks during search operations.
6. Troubleshooting and Maintenance: Several technical tips and interoffice memoranda detail common issues and solutions. These include electrical problems like drive motor grounding causing noise, wiring errors leading to erased block numbers, and microtape operational issues such as faulty selector switches, loose/tight hubs, tape coasting, marginal records, and noise spikes affecting error flags. It also specifies timing restrictions for commands based on relay operate times.
7. Associated Programs: The document describes various programs designed for the tape system:
   • Micro Tape Data Test: Checks data transfer and flag detection.
   • Micro Tape Dump and Retrieve: Stores and retrieves data on tape.
   • Micro Tape Exciser: Exercises tape by writing and reading blocks in specified areas.
   • Micro Tape Format Pack: Writes the mark, timing, and block numbers to tape, and allows checking.
   • Micro Tape Rocker Program: A debugging tool that oscillates tape over a desired area or between blocks, with options for searching, reading, writing, and scope synchronization.