we found the pin 1 should be 3.3v from description of GPIO Pin Assignments, but I get only 0.75v via multimeter,What‘s the reason?
You’re comparing it to what ground?
use the Pin9 as ground, I have found the role cause that supply current is lower with using the USB port of my PC. It’s necessary for using 5v adaptor for power supply.
You are right,bro
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Power supply is from usb-c using USB PD protocol controlled by the CH224D. It is configured to request 12v from the external USB power supply which feeds into the NB679 buck regulator to provide the 5v (up to 8amp) supply to the board.