0

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.

Mark Estrada
  • 133
  • 1
  • 6

1 Answers1

2

There is an image which shows default pullup (among other things) http://www.panu.it/raspberry/

NOTE the above is not strictly correct for the Pi4. The Pi4 default pin settings (and most common optional settings) are identical, but the Pi4 has additional settings for some pins.
See Pi4 GPIO

The BCM2711 ARM Peripherals which can be downloaded is the official Pi4 documentation. Section 5.3. Alternative Function Assignments shows possible functions.

The Answer by joan explains and references the official documentation https://raspberrypi.stackexchange.com/a/32643/8697

The command

raspi-gpio get

will show the the ACTUAL state of GPIO (including pullups for Pi4 only). See https://raspberrypi.stackexchange.com/a/113414/8697

PS Using a multimeter is not a reliable method of determining pullup.

Pins 14,15 are configured as serial. TxD is an OUTPUT.

Milliways
  • 62,573
  • 32
  • 113
  • 225