When a system boots, the BIOS or controller reads the SPD data to configure the memory controller correctly. However, if an SPD chip becomes corrupted, misconfigured, or needs to be reprogrammed, you must to bypass normal read-only operations and gain low-level access for testing, reading, or writing.
Entering diag mode is not a single command but a sequence of writes to specific registers. enter diag mode spd
To confirm the device is in Diagnostic Mode, check your : Look under the Ports (COM & LPT) section. When a system boots, the BIOS or controller