PDP-7 Symbolic Assembler

This document is the programming manual for the PDP-7 Symbolic Assembler, a software tool designed to simplify programming for the PDP-7 computer by allowing users to write code in a more convenient, human-readable language rather than 18-bit binary numbers. It covers the advantages of assembly programming, such as using mnemonic codes, symbolic names for instructions and data, easier debugging, and flexible program modification.

The assembly system comprises the Assembler and the FF Loader. The Assembler takes a source program (written in ASCII or FIODEC code) in a single pass and produces an object tape in FF Binary code. The FF Loader then loads this binary program into the computer for execution, handling tasks like resolving undefined symbols and setting up constant tables that cannot be completed during the single assembly pass. The Assembler requires a basic 4K memory configuration, a teleprinter, a tape reader, and a tape punch, with varying symbol storage capacities depending on memory size.

The manual details the PDP-7 Assembler's features, including the location counter (which tracks memory addresses), coding using octal codes, symbolic instruction names, and symbolic address tags. It explains how to define constants and variables (including automatic storage assignment), use expressions with arithmetic/logical operators, and incorporate comments. The structure of source language statements and instructions is also described.

Program preparation involves creating a punched paper tape with a title, the program body (statements and pseudo-instructions), and a terminating pseudo-instruction (START or PAUSE). The Assembler's output includes the binary object tape (with its own title, the FF Loader, program data blocks, and termination block), error messages, and optional printouts of user-defined symbols. Operating instructions cover loading the Assembler, processing symbolic tapes, controlling assembly options via AC switches, handling multiple source tapes, and loading symbol punches. Halts during assembly and object program loading (e.g., checksum errors) are also addressed.

Appendices provide a comprehensive list and explanation of pseudo-instructions (commands that control the assembly process but do not generate binary code), the Assembler's permanent symbol table (with options for modification), and details about the FORTRAN Assembly System. The FORTRAN Assembler is a modified version that produces relocatable object programs and includes additional linking pseudo-instructions for managing subroutines and library routines across different program segments. Finally, a character set comparison for ASCII, FIODEC, and Teletype (Baudot) is included.