Hello YuChia Chien,
-Under MCUXpresso SDK , there is a demo " power_manager_lpc" shows the usage of normal power mode control APIs for entering the three kinds of low power mode: Sleep mode, Deep Sleep mode and Sleep Power Down mode.
The device can be also waken up by prepared wakeup source ( GPIO pin interrupt 0 )from external event .
You can download the SDK package from NXP website : https://mcuxpresso.nxp.com/en/select

then can find this demo under : SDK_2.3.0_LPCXpresso51U68\boards\lpcxpresso51u68\demo_apps\power_manager_lpc .
- About "Is a specific GPIO pin need to be selected?"-> By configure the "Pin interrupt select register" to select
which pin to Pin interrupt. In this demo , use SW3(P0_24) .
Hope it helps,
Have a great day,
TIC
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------