Focalp - Focalpe

This document serves as a user manual/write-up for FOCALP/FOCALPE, a version of FOCAL 5/69 specifically tailored for the 4K PDP-12A computer equipped with an incremental plotter.

Key highlights include:

• System Requirements & Loading: The program is designed for use with a DIAL V2 tape. It is available in two versions: one with extended functions and one without.

• Command Improvements: Several standard FOCAL commands have been enhanced. Notable changes include:

  • ASK: Now operates in either Interpretive (accepts expressions/numbers) or Character (accepts ASCII characters) mode.
  • DO: Supports executing multiple line numbers in sequence and allows for calculated line numbers (expressions) as arguments.
  • FOR: Added support for negative increments (backward counting) and conditional execution based on initial versus final values.
  • ERASE/MODIFY/GOTO: These commands now support calculated line numbers.
  • HELLO: A new command introduced to quickly initialize FOCAL to its default state.

• Plotter Support: New commands (PLOT/P) are included to control an incremental plotter, allowing the user to establish zero references, move the pen, and draw lines based on mathematical expressions.

• Storage & Performance: The document provides detailed technical information regarding memory usage (user area), the pushdown list, and formulas for calculating required storage based on program length and variable count.
• Diagnostics: The manual concludes with a comprehensive list of error diagnostic codes (e.g., ?11.18 for input buffer overflow or ?02.81 for pushdown list overflow) to assist in debugging.
• Technical Notes: It clarifies changes to arithmetic priorities (conforming to standard algebra/FORTRAN), function behavior (FITR, FSGN, FRAN), and specific handling of input/output buffers and character sets.