Editing Diagnostic Serial Console (section)

=== Memory Configuration Detection Patterns ===

The diagnostic system provides precise SIMM slot detection through specialized response codes that accurately reflect physical memory installation. When testing partial SIMM configurations, the <code>*R</code> command returns specific patterns indicating slot population status. With 1MB SIMMs installed in slots 1 and 2 only, the system reports <code>0000FFFF000E</code>, while installation in slots 3 and 4 only produces <code>FFFF000000E</code>. These codes provide immediate verification of physical SIMM installation and can diagnose installation errors or socket problems.

Memory addressing behavior reveals precise hardware functionality when writing test patterns to address 0x00000000. With 1MB SIMMs in slots 1 and 2 only, writing the pattern <code>11223344</code> reads back <code>xxxx3344</code>, indicating that slots 1-2 correspond to the lower 16 bits of the 32-bit data bus. Moving the SIMMs to slots 3 and 4 results in reading back <code>1122xxxx</code>, confirming that slots 3-4 handle the upper 16 bits. This demonstrates that the diagnostic interface can access each SIMM slot independently and reveals the precise relationship between physical slot positions and data bus bit assignments.