What is the default settings of gpio signal in output mode?

When a gpio located on the HAT connector is set as output, what is the default output mode? Pull up resistor of 100k, open collector or ?
Is there any electrical specification of the gpio signal for the UP Xtreme board?

I Use UP Xtreme and this is the how I do the configuration:

echo 22 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio22/direction


  • jayman
    jayman New Member Posts: 66 ✭✭
    edited June 2021

    Keep in mind that the HAT GPIOs are level-shifted by the MAX V CPLD, so the characteristics you're seeing at the HAT pin are not dictated by how you program the GPIO, but by how you configure the HAT in BIOS. Each GPIO can be set as Input/Output, and when set to Output it can further be set to default High or default Low (both in push-pull mode).

    Of course for your GPIO pins to work correctly, the configuration of the pin itself has to match the configuration of the CPLD in BIOS.

  • Pratik_Kushwaha
    Pratik_Kushwaha Guest Posts: 123 admin

    Hi @tomass ,

    When GPIO pin set as output, the default output mode is push-pull, and pull-up 2.2K by internal CPLD chip.
    When GPIO pin set as input, the default input mode is open-drain (Open-Collector).


  • tomass
    tomass New Member Posts: 3

    Thanks @jayman and @Pratik_Kushwaha! This brought lights on my thoughts.

  • tomass
    tomass New Member Posts: 3

    In BIOS I could just set the default high/low for output and no options for input! Is there another menu in BIOS for the more specified options like (input) pull-up/down resistor value, (output) open collector, push-pull ?