I have read somewhere, but I have not bookmarked it. Maybe it was a post in one of the forum for Rpi that
- GPIO 0-8 are pull up enabled when the Pi starts up
- GPIO 9-27 are pulled down enabled when Pi starts up
I tried to validate that in my RPi 4 Model B, I tested GPIO Pins 0 to 8 when the RPi boots up and I connected my multimeter to ground for each GPIO Pins.
I checked that the output from GPIO 0-8 is indeed 3.3 or less, the other Pins are 0V.. however when I checked, GPIO 14 and GPIO 15 which is TXD and RXD use, I am getting a 3.3 v also.
Is what I have read wrong? I can't find a documentation about this.
UPDATE I executed the command suggested and I was able to verify that it GPIO 14 and GPIO 15 was indeed pulled up.
raspi-gpio get BANK0 (GPIO 0 to 27): GPIO 0: level=1 fsel=0 func=INPUT pull=UP GPIO 1: level=1 fsel=0 func=INPUT pull=UP GPIO 2: level=1 fsel=4 alt=0 func=SDA1 pull=UP GPIO 3: level=1 fsel=4 alt=0 func=SCL1 pull=UP GPIO 4: level=1 fsel=0 func=INPUT pull=NONE GPIO 5: level=1 fsel=0 func=INPUT pull=UP GPIO 6: level=1 fsel=0 func=INPUT pull=UP GPIO 7: level=1 fsel=1 func=OUTPUT pull=UP GPIO 8: level=1 fsel=1 func=OUTPUT pull=UP GPIO 9: level=0 fsel=4 alt=0 func=SPI0_MISO pull=DOWN GPIO 10: level=0 fsel=4 alt=0 func=SPI0_MOSI pull=DOWN GPIO 11: level=0 fsel=4 alt=0 func=SPI0_SCLK pull=DOWN GPIO 12: level=0 fsel=0 func=INPUT pull=DOWN GPIO 13: level=0 fsel=0 func=INPUT pull=DOWN GPIO 14: level=1 fsel=2 alt=5 func=TXD1 pull=NONE GPIO 15: level=1 fsel=2 alt=5 func=RXD1 pull=UP
In Page 102,of this https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2835/BCM2835-ARM-Peripherals.pdf documentation, it says that GPIO 14 and GPIO 15 should indeed be pulled down. So is there something in my setup that is pulling this up?
Note I just rebooted my Rpi 4 several times.