Before the power button is even pressed, the motherboard must establish baseline voltages to listen for a wake signal.
The power-on process moves through several distinct states, often following ACPI standards from to S0 (Working State) . 1. Pre-Trigger / Standby Phase (G3 to S5) desktop motherboard power sequence pdf exclusive
The is a highly structured, step-by-step process that ensures all components—from the chipset to the CPU—receive stable power in the correct order to prevent hardware damage and ensure a successful boot. Understanding this sequence is essential for diagnosing "no power" or "no display" issues. Core Stages of the Power Sequence Before the power button is even pressed, the
This phase initiates the transition from a "Soft Off" (S5) state toward full operation. Desktop Motherboard Power Sequence Explained - Scribd Pre-Trigger / Standby Phase (G3 to S5) The
: The CMOS battery provides voltage to the Southbridge/PCH to maintain the Real-Time Clock (RTC).
: When the ATX power supply is plugged in, it immediately sends +5V standby (purple wire) to the Super I/O (SIO) chip.
: The SIO sends this 3.3V high-level signal to the PCH to notify it that standby power is stable and the system is ready to be "resumed". 2. Triggering Phase (Power Button Event)