LA100-Series Programmer Reference Manual

This document is the LA100-Series Programmer Reference Manual, published in January 1982 by Digital Equipment Corporation. It serves as a technical guide for programmers developing application software for the LA100 Letterprinter terminals.

The manual is divided into two main chapters:

1. Communication: This chapter details the terminal's communication interfaces and features. It covers:

   • Serial Character Format: How the LA100 communicates via serial characters, including start/stop bits, data bits (7 or 8), and parity.
   • EIA Interface (RS-232-C/V.24): A detailed description of the DB-25 connector, its pins, and signals like Transmitted Data (TXD), Received Data (RXD), Request to Send (RTS), Clear to Send (CTS), Data Set Ready (DSR), Signal Ground, and Receive Line Signal Detect (RLSD), explaining their functions and directions.
   • Modem Control: Discusses full-duplex communication with or without modem control and how it affects EIA signals.
   • Full-Duplex Disconnect: Conditions that trigger a terminal disconnect.
   • Input Buffer Overflow Prevention: Explains the 400-character input buffer and methods to prevent overflow, including XON/XOFF and restraint features, using "fill characters" (like NUL) to slow data transmission, and limiting message size. It provides formulas and tables for calculating required fill times based on character execution rates and printhead movements (horizontal and vertical).

2. Character Processing: This chapter describes how the LA100 terminal responds to received characters, adhering to American National Standards Institute (ANSI) standards (X3.64-1979, X3.4-1977, X3.41-1977). It covers:

   • Printable Characters: How they are stored and printed.
   • Control Characters: Single-character functions (e.g., NUL, Bell, Backspace, Line Feed, Form Feed, Escape) that control terminal operations without being printed.
   • Escape and Control Sequences: Multi-character commands that provide advanced control functions. These sequences manage various printer settings, including:
     • Line Feed New Line Mode and Auto Wraparound Mode.
     • Print Quality (draft, medium, high density).
     • Font Selection and Character Set Designation (e.g., USASCII, various ISO and Digital language sets).
     • Horizontal and Vertical Pitch (characters/lines per inch) and Margins.
     • Tab Stops (horizontal and vertical).
     • Form Length (form mode vs. roll paper).
     • Active Column and Active Line (current print position).
     • Product Identification queries.
   • Graphics Mode: Details how the terminal enters and operates in graphics mode, where characters define columns of dots for drawing. It describes the graphics string format (DCS introducer, protocol selector, data, DCS terminator), graphics-specific control characters, how printable data defines dot patterns for the 6-wire printhead, and repeat sequences for efficient graphics printing.
   • Answerback Message Entry: How to program and enable a terminal identification message (up to 30 hexadecimal-encoded characters) that can be transmitted upon request.

The manual emphasizes that proper configuration of the application program, terminal handler, and general terminal settings is crucial for desired terminal actions.