Power Control & Status¶

Status Indication¶

LattePanda Mu x86 compute module provides two status output pins, PSON and SLP_S4, to indicate the current system power state (e.g., S0, S3). These pins are dedicated to controlling the power enable lines for peripherals or to drive status LEDs.

Pin Definition¶

Pin Name	Pin Number	Note
PSON	5	Output HIGH(Weak Drive) only when S0(Working)
SLP_S4	7	Output HIGH only when S0(Working) and S3(Sleeping)

Note

The PSON pin relies on the 10kΩ pull-up resistor to output HIGH. It cannot source significant current (max source current is approximately 0.33 mA). Thus, an external NMOS is required to drive an LED indicator or other components that need higher current.
When the LattePanda Mu compute module is powered but not started while the RTC battery is missing or low, the SLP_S4 pin will output HIGH. In this case, please assemble a new RTC battery and complete one full power cycle (power on and then power off). After this, SLP_S4 pin's level indication will function normally as described in the table above.

Status Logic Table¶

System State	PSON Level	SLP_S4 Level	Note
Working (S0)	HIGH	HIGH	System running normally
Sleep (S3)	LOW	HIGH	Suspend to RAM
Hibernate (S4)	LOW	LOW	Suspend to Disk
Shutdown (S5)	LOW	LOW	Soft OFF
Standby (G3)	LOW	LOW	Powered but not Turned ON

The above logic simplifies the power enable control of peripherals and the driving of status LEDs, and can be implemented purely in hardware.

Examples will be given separately below.

Peripheral Power Control¶

As shown in the schematic above, using SLP_S4 to control the EN pin of the DCDC Buck chip allows the 5V power supply to remain on in working and sleep states. In other states, such as shutdown or standby, the 5V power is cut off. This 5V power logic is suitable for USB ports and similar applications.

If 5V power is only needed in the working state, the DCDC Buck chip's EN pin can instead be controlled by PSON.

Status LED Drive¶

As shown in the schematic above, the following behavior is achieved:

When powered on(in working mode), only the left LED illuminates.
In sleep mode, only the right LED illuminates.
In other states, such as power off or standby, both LEDs are off.

These two LEDs can be set to different colors(e.g. blue, green) to reflect the current status.

Power Control¶

LattePanda Mu x86 compute module provides signal lines for power and reset buttons, which function exactly like those on a standard laptop or desktop computer.

Pin Definition¶

Pin Name	Pin Number	Note
PWR_SW#	1	System Power Switch; Internally 10K Pulled Up
RST_SW#	3	System Reset Switch; Internally 10K Pulled Up

PWR_SW#¶

Connect to a physical power button. Active Low.
A low pulse duration of ≥ 125ms is recommended for reliable detection.
Holding Low for > 4 seconds will trigger a forced shutdown.

RST_SW#¶

Connect to a physical hard reset button. Active Low.
A low pulse duration of ≥ 16ms is recommended to ensure a successful reset.

ESD Protection¶

Since buttons are frequently touched, they are vulnerable to electrostatic discharge (ESD). Adding ESD protection diodes is strongly recommended.

Reverse Working Voltage: 5V

FAQ¶

Question	Potential Cause / Check Point	Explanation / Solution
CMOS Error appears after boot	Low RTC battery voltage	Replace the RTC battery with a new one.
	First initialization after BIOS update	This is normal behavior. The message will disappear once initialization is complete.
Boot process is extremely slow every time	`PWR_SW#` pin held low (>10s) before booting	If the `PWR_SW#` is held for over 10s, it triggers a BIOS Reset. The subsequent boot requires full hardware re-initialization, causing a significant delay.
Powered but not started, `SLP_S4` pin output HIGH	Low RTC battery voltage	Replace the RTC battery with a new one. Then complete one full power cycle (power on and then power off).
	First powered but not started after being assembled into the carrier board	Ensure the RTC battery is assembled. Then complete one full power cycle (power on and then power off).