Basic PDP-8, 8/I Memory Checkerboard

Summary

This document provides the technical specifications, operating instructions, and program listing for the "Basic PDP-8, 8/I Memory Checkerboard" diagnostic tool.

Purpose: The diagnostic program is designed to test core memory in PDP-8 and 8/I systems for potential failures. It specifically identifies errors related to "half-selected" lines under worst-case operating conditions.

Key Information:

• Versions: There are two versions of the program—a "Low End" version (testing memory locations 151–7700) and a "High End" version (testing 0000–7400).
• Operation: The program writes specific checkerboard patterns to memory, reads them back, complements the data, writes it back, and checks for bit errors. The process runs until stopped by the operator or an error is detected.
• Error Handling: If an error is detected, the program halts. The Accumulator (AC) is used to display either the incorrect contents of the memory location or the address of the location in error, allowing for troubleshooting.
• Technical Context: The document includes an explanation of core memory logic, detailed switch settings for different hardware configurations, and the full assembly language source code for both the 1968 and 1969 revisions.