This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later.

: The SIO sends this 3.3V signal to the PCH, indicating that standby power is stable and the "resume" logic is ready. Phase 2: Power Request & Initiation Desktop Motherboard Power Sequence Explained - Scribd

The power button pulls a high signal (3.3V) to ground (0V) at the Super I/O.

Analysis of the PSIN/PSOUT signals when the power button is pressed, initiating communication between the SIO and PCH.

PWR_OK must go high 100ms to 500ms after PS_ON# is pulled low. If PWR_OK does not arrive within this window, the motherboard assumes a faulty PSU and aborts.

The desktop motherboard power sequence is a highly logical, deterministic cascade. By understanding the dependencies—how standby power enables the Super I/O, how the Super I/O wakes the PCH, and how the PCH coordinates with the PSU and CPU VRMs—diagnosing complex hardware failures changes from guesswork into a precise, step-by-step science.