Pdp-8, 8/I, Extended Memory Address Test

This document serves as the technical documentation and program listing for the "PDP-8, 8/I, Extended Memory Address Test," a diagnostic tool created in 1968 by Digital Equipment Corporation.

Purpose: The program is designed to verify that every memory location in a PDP-8 or 8/I computer (equipped with the extended memory option) can be addressed and accessed correctly. It ensures that memory not occupied by the program is functioning properly.

Key Features and Functionality:

• Testing Methodology: The diagnostic runs four distinct tests on all available core memory:

  1. Writes the address and its complement into each memory location and verifies it.
  2. Writes the ones complement of the address into each location and verifies it.
  3. Performs a "sliding" bit test, where a single bit (1 or 0) is shifted through every memory location to check for errors.

• Automatic Relocation: The program is capable of automatically relocating itself into different memory fields, ensuring that all available memory can be fully tested.

• Operator Control: Using the computer's Switch Register (SR), operators can:
  • Select specific memory limits for testing.
  • Inhibit error printouts or enable audible alerts via the TTY bell.
  • Control test selection and program relocation.
  • Loop on a specific memory address for troubleshooting purposes.

Requirements: The diagnostic requires a standard PDP-8 or 8/I system with a minimum of 8K words of core memory. The document also includes a complete source code listing and symbol table for the diagnostic program.