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This technical memorandum, dated October 30, 1967, describes the PDP-X/II Programmers Console, authored by H. Burkhardt.

The console serves two primary functions:

1. Debugging: Allows programmers to examine and modify the machine and program state.
2. Maintenance/Troubleshooting: Provides information about the processor state.

This document focuses specifically on the console's role as a debugging tool. While large system debugging often relies on software, smaller configurations depend on the console for tasks like single-stepping, memory examination/modification, and observing processor/I/O device states. Operators also use the console to start/stop programs, reset the I/O system, and initiate program loading.

The PDP-X/II console is comprised of three main types of controls:

1. Indicators: Display the internal state of the computer. These include:

   • RUN: Processor execution status.
   • SR (Status Register): Current process status word.
   • IR (Instruction Register): Instruction being executed or last executed.
   • MI (Memory Interface): Address of the next instruction or examined/deposited word.
   • CI (Console Indicators): A register loadable by program or HLT instruction.
   • PI EXR, PI INR, PI INH, PI ACT (Program Interrupt indicators): Display external, internal, inhibited, and active program interrupt requests and levels.

2. Switches: Provide input and configuration settings. These include:

   • CSW (Console Switches): 16 switches used for manual data/address entry (in conjunction with keys) and device selection for program loading.
   • POWER: Controls primary power to the system.
   • CONSOLE LOCK: Locks/unlocks the console keys and switches.

3. Keys: Trigger specific actions and operations. These are momentary or two-position controls:

   • SI (Single Instruction): Steps the program one instruction at a time.
   • STOP: Halts processor execution.
   • RESET: Stops the processor, resets the I/O system, clears interrupt registers, and sets initial conditions.
   • CONTINUE: Resumes program execution from the stopped point.
   • START: Loads the program counter from the CSW and begins execution.
   • READIN: Resets I/O, clears interrupt registers, and initiates program loading from a device selected via CSW.
   • EXAMINE: Displays the contents of a memory word (specified by CSW) in the CI and its address in the MI (if processor is stopped).
   • DEPOSIT: Places CSW contents into the CI and the memory location specified by MI.
   • EXAMINE NEXT: Increments MI and displays the next memory word in CI.
   • DEPOSIT NEXT: Increments MI and deposits CSW contents into the next memory location.