PDP-9 Basic Memory Checkerboard Test

This document describes the PDP-9 Basic Memory Checkerboard Test, a diagnostic program designed for a quick verification of core memory operational status on a PDP-9 system. Its primary function is to test an 8K memory bank's ability to correctly detect "1" or "0" bits under maximum half-select noise conditions.

The program requires a standard PDP-9 with a minimum of 8,192 words of core memory and occupies approximately 350 (octal) words of memory. It is loaded via an HRI mode binary tape and automatically starts execution. The test systematically applies four different checkerboard patterns to the memory, loading, reading, and testing each pattern multiple times. It dynamically relocates itself between the lower and upper 4K sections of an 8K memory bank to ensure comprehensive testing of the entire bank.

In the event of an error, the program halts, displaying the memory address where the error occurred, the correct data word, and the incorrect data word. Operators can then use AC switches to suppress further testing of identified faulty bits. A full diagnostic pass for an 8K memory bank takes approximately 8 seconds. The document suggests using the PDP-9 Extended Memory Test for more thorough memory evaluations.