The SIO pulls the green wire on the 24-pin ATX connector to 0V (ground), telling the PSU to turn on all main rails (12V, 5V, and 3.3V).
Pressing the power button sends a signal to the SIO, which then communicates with the South Bridge (PCH). Wake-Up Signals: The South Bridge responds with desktop motherboard power sequence pdf
: Once all voltages are confirmed stable, the PCIRST (System Reset) signal is released, and the CPU begins executing BIOS instructions. The SIO pulls the green wire on the
This phase begins the moment you press the physical power button on your case. This phase begins the moment you press the
A desktop motherboard power sequence is the specific order in which electrical signals and voltages are activated to safely transition the system from an "off" state to a fully functional operating state. Understanding this sequence is vital for diagnosing "No Power" or "No Display" issues. 1. Standby Phase (S5 State)