VT55 Programming Manual

This document is the VT55 Programming Manual, published in February 1977 by Digital Equipment Corporation for its PDP-11 systems.

The manual serves as a guide for programmers familiar with PDP-11 FORTRAN (for RT-11, RSX-11M/D, and IAS operating systems) or BASIC-PLUS (for the RSTS/E operating system), demonstrating how to program the VT55 terminal to leverage its graphical capabilities.

Key aspects of the manual include:

1. VT55 Modes: It explains the three operational modes of the VT55 terminal:

   • Alphanumeric mode: The default mode for standard ASCII text.
   • Graphic mode: For displaying graphic figures using special instructions.
   • Escape mode: A temporary mode for immediate control functions like screen erasure or hard copy. The software automatically switches between modes as needed.

2. Graphic Figures: The VT55 can display various graphic elements:

   • Graphs (as points or line segments)
   • Shaded Graphs (filled areas below the function)
   • Markers (short vertical lines)
   • Horizontal and Vertical lines (spanning the screen) It details how to enable, select, and plot these figures, which involves using internal graphic memory registers.

3. Programming Interfaces:

   • FORTRAN: Control is primarily through a single subroutine called PLOT55. Different ICMD (integer command) values specify the desired procedure, such as attaching/detaching the terminal, selecting graph numbers, enabling/disabling graphic figures, plotting points or arrays, drawing lines and markers, positioning the cursor, erasing/displaying alphanumeric text, and sending escape sequences.
   • BASIC-PLUS: Four specific functions (FNV5, FNV6, FNV7, FNV8) are provided via the VT55.BAS file:
     • FNV5: A general graphic function for displaying graphs, markers, vectors, and lines, as well as terminal control, cursor positioning, and hard copy.
     • FNV6: For displaying alphanumeric text.
     • FNV7: An initialization function to reset the screen.
     • FNV8: For displaying "step" histograms (vertical bar graphs).

4. Key Concepts: The manual defines terms like logical unit numbers, terminal numbers, event flags (for task synchronization in larger systems), and the coordinate systems for both graphic (X: 0-511, Y: 0-235) and alphanumeric (X: 0-79, Y: 0-23) displays. It also explains how to plot graphs using one-dimensional arrays and draw vectors.

5. Setup and Applications: It provides detailed procedures for assembling and linking PLOT55 for FORTRAN programs or appending VT55.BAS for BASIC-PLUS programs. Appendices offer suggested higher-level routines for common tasks like grid drawing, automated graph plotting, and shading.

In essence, the manual equips programmers with the fundamental commands and concepts needed to develop applications that generate and manipulate graphic and alphanumeric displays on the VT55 terminal.