Conclusion The desktop motherboard power sequence is a deterministic, signal-driven choreography ensuring reliable startup. While the ATX PS_ON/PWROK model remains a conceptual baseline, modern motherboards require fine-grained sequencing across many domains, enforced by combined hardware (VRMs, PMICs, supervisors) and firmware (SIO/EC, BIOS). For hands-on repair or design, consult platform-specific PDFs and signal-ladder diagrams to get exact timings, thresholds, and signal names.
The SIO pulls the PS_ON signal (green wire on the SMPS) low (0V), triggering the power supply to turn on fully and provide 3.3V, 5V, and 12V. Secondary Voltages: desktop motherboard power sequence pdf exclusive
The PSU immediately sends a 5V standby signal (purple wire) to the SIO chip and PCH. Conclusion The desktop motherboard power sequence is a
Confirmation to the CPU/PCH that all voltages are stable and within spec. PCH → CPU The SIO pulls the PS_ON signal (green wire
The CPU receives its reset signal and begins executing the first line of code from the BIOS/UEFI chip.