DDT Macro Assembly Instructions

This document details the assembly instructions for various versions of the DDT (Dynamic Debugging Technique) program, controlled by the EDDT symbol. The EDDT symbol dictates assembly options such as user or executive mode, paper tape features, I/O handling (e.g., TTCALL, DOTIN, ODTOUT UUOs), and whether the output is relocatable or absolute with a specified starting address.

The document defines numerous internal components:

• Accumulators (registers) and their specific uses.
• I/O device mnemonics.
• Flag bits within accumulator F for controlling input/output operations.
• Symbol table types including GLOBAL, LOCAL, PNAME, and DELETE flags.
• Macro assembly commands and examples for creating customized DDT versions (e.g., relocatable user mode, absolute executive mode with paper tape features).

It further describes routines for input/output processing, symbol table management, register examination, breakpoint logic, memory fetch and deposit operations, numeric and symbolic output, and the opcode decoding mechanism. The opcode decoder section explains how PDP-6 instructions are compactly represented and interpreted from a byte-based lookup table.