Digital Ansi-Compliant Print Protocol Lev 2 Program. Ref. Man.

This manual is a programming reference for Level 2 of Digital's ANSI-Compliant Printing Protocol (DEC PPL2), detailing printer functions for all Level 2 compatible printers.

The document covers:

1. Protocol Concepts: It defines the tiered structure of Digital's printing protocols (Level 1 for basic character cell, Level 2 for advanced character cell with more positioning and font capabilities, and Level 3 for page printers). This manual specifically focuses on Level 2, which includes all Level 1 functions. It also distinguishes between protocol extensions (device-independent features) and exceptions (device-specific features) and the roles of applications vs. symbionts (drivers) in printer control.
2. Character Processing: It describes how characters are coded (7-bit and 8-bit), categorized (C0/C1 control, GL/GR graphic, special characters), and selected for printing. It also details the formats of control functions, including escape sequences, control sequences (like CSI for parameter-driven commands), and variable-length control strings (like Device Control Strings - DCS).
3. Page Coordinate System: It explains the character cell model used by Level 2 devices for page layout, defining active print position, horizontal and vertical advance increments (HAI/VAI), and various positioning controls. It also covers margin management (top, bottom, left, right) and concepts like partial line motion (PLU/PLD) and conditional form/sheet feeds.
4. Fonts: It differentiates between graphic character sets (what is printed) and fonts (how it is printed, including typestyle and density). It outlines the font repertory (built-in, cartridge, and downloadable fonts) and the font selection process based on a "Current Font Definition" and fallback mechanisms.
5. Sixel Graphics: A dedicated section describes the Sixel Graphics protocol for transmitting and printing bitmap data. It explains fundamental concepts (pixels, sixels, scan lines, grid), how to enter and exit Sixel Graphics mode using a Device Control String (DCS), and specific Sixel control codes for color, movement (Graphics Carriage Return, Graphics Next Line), raster attributes, and repeat sequences.
6. Control Characters and Command Dictionary: The manual provides detailed descriptions of all C0 and C1 control characters and a comprehensive dictionary of DEC PPL2 commands and reports, organized by function, including their formats, descriptions, side effects, and error handling.