PDP-9 Extended Memory Test

This document describes the PDP-9 Extended Memory Test (MAINDEC-9A-D1BA-D), a diagnostic program designed to verify the operational status of core memory (ranging from 8,192 to 32,768 words) by testing its ability to detect '1's and '0's under maximum half-select noise conditions.

The program is loaded from an HRI binary tape, and the operator configures Accumulator Switches (ACS 14-17) to specify the memory range to be tested. The test sequence involves three primary subtests:

1. Sliding Zero (ACS 3): This subtest fills memory with '1's, then systematically complements, stores, reads, complements, stores, and re-tests each bit for errors.
2. Worst Case Checkerboard (ACS 4) and Complement Worst Case Checkerboard (ACS 5): These subtests utilize two distinct checkerboard patterns (and their complements for ACS 5) that are loaded into memory in defined blocks. After multiple rapid reads, a final pass performs detailed error checking by reading, complementing, depositing, rereading, and comparing the data.
3. Data Retention Test (ACS 6): This subtest loads a checkerboard pattern, halts the program to allow for a power cycle (AC power off/on), and then reads and verifies the pattern's retention.

The test program includes automatic program relocation to systematically move between memory banks, ensuring all selected memory areas are tested. Upon error detection, the program provides detailed printouts including the subtest number, octal address, bad data read, expected good data, and the specific pattern or bit being tested. Operators can customize the test behavior using various Accumulator Switches (ACS): halting the program (ACS 0), inhibiting error printouts (ACS 1), ringing a bell on error (ACS 2), selecting specific subtests (ACS 3-6), activating continuous write/read 'scope modes (ACS 7-8), preventing program relocation (ACS 9), and suppressing testing of specific bits (ACS 10). Restarting options are available to either fully reset the program (address 00021) or continue with existing parameters (address 00043). It is recommended that basic memory address and checkerboard tests be successfully completed before running this extended test. The document also details the precedence of ACS functions and lists significant memory locations within the program.