Magtape Focal

Summary

MAGTAPE FOCAL is a software handler package designed for the DECUS Program Library, intended to facilitate the use of the TC58 IBM-compatible magnetic tape controller and TU28 7-track tape unit on an 8K PDP-8/I computer. The primary purpose of this program is to eliminate the necessity for users to program tape operations in assembly language by providing a sophisticated handler within the FOCAL language environment.

Key features and capabilities include:

• Library Interface: The handler uses the FOCAL LIBRARY command structure to execute tape operations (e.g., REWIND, SPACE, WRITE, GET, INITIALIZE, EOF, CLEAR).
• Data Storage: It utilizes the FNEW function to address data in FIELD 1, allowing for larger variable storage and efficient data transfer between the tape controller and the computer’s memory.
• Functionality: It supports I/O overlap with program execution, programmable tape density, unit selection, and extensive error checking.
• Error Handling: It includes diagnostic messages for common errors, and allows the evaluation of tape controller status via a preempted FADC function to identify specific issues like end-of-file, parity errors, or incorrect record lengths.
• Compatibility: The package is provided in two dialects: one for 36-bit PDP-8 floating-point format and another for 12-bit PDP-8 integers.

The document includes a detailed write-up, usage instructions, examples of FOCAL commands, diagnostic tables, and the complete assembly-level source code for the handler.