PDP-X Instruction Simulator

This document details an instruction simulator for the PDP-X (Model II), designed to run on a PDP-9 or PDP-7. Its main purpose is to facilitate debugging of system and diagnostic software for the PDP-X, and to offer insights into its implementation. The simulator emulates key PDP-X features such as traps, two interrupt levels, teletype and paper tape I/O, an extended instruction set, and advanced console features, but notably does not simulate the Multiplexor Channel.

Operating on a PDP-9, the simulator processes PDP-X memory cycles at 250-400 microseconds per cycle, with more complex instructions running slower. It consumes approximately 2400 words of PDP-9 memory.

The user interacts with the simulated PDP-X console through the host system's teletype and AC (front panel) switches, using commands similar to DDT. This allows for examining and modifying PDP-X memory (in octal or instruction format), resetting the I/O system, initiating paper tape readin, and controlling program execution (start, continue). Run control is managed via AC switches, providing functionalities such as Single Instruction stepping, Hard Stop (halting the PDP-9), Repeat (restarting PDP-X after a stop), Memory Disable (stopping on non-existent memory access), and Address Stop (stopping when a specific memory address is accessed). The document concludes with straightforward instructions for loading the simulator from paper tape.