Is it possible to use internal pull-up/pull-down resistors with I2C, UART, etc?

[nategreco]

I need pull-up/pull-down resistors on my UART and I2C lines and am wondering if I can enable the pull-up/pull-down resistors instead.  If this possible?  I can see how to configure them for GPIO, but I'm wondering if I use the same approach if it would interfere with the UART/I2C drivers.  Thanks

Other info:
nRF52480

nRF Connect SDK v2.1.0

[nategreco]

After some digging, I found in `nrf_twim.c`:

#define TWIM_PIN_INIT(_pin, _drive) nrf_gpio_cfg((_pin),                     \
                                                 NRF_GPIO_PIN_DIR_INPUT,     \
                                                 NRF_GPIO_PIN_INPUT_CONNECT, \
                                                 NRF_GPIO_PIN_PULLUP,        \
                                                 (_drive),                   \
                                                 NRF_GPIO_PIN_NOSENSE)

Looks like both the SDA and SCL lines have the pull-up resistor enabled by default.  For UART, this is what I've found so far in `nrfx_uarte.c`:

        if (p_config->pseltxd != NRF_UARTE_PSEL_DISCONNECTED)
        {
            nrf_gpio_pin_set(p_config->pseltxd);
            nrf_gpio_cfg_output(p_config->pseltxd);
        }
        if (p_config->pselrxd != NRF_UARTE_PSEL_DISCONNECTED)
        {
            nrf_gpio_cfg_input(p_config->pselrxd, NRF_GPIO_PIN_NOPULL);
        }

Looks like the RX pin does NOT use a pull-up, which is what I'd like.

So maybe two questions:

1. Is my understanding correct?  By default with twim 13k pull-up resistors are enabled for both SDA and SCL?  And for UART RX does not enable by default?
2. Is there any way to enable the pull-up for my UART RX line within my application instead of modifying my library?

Thanks

[Håkon Alseth]

Hi,

 

You can set bias pull in DT, similar to this:

https://github.com/nrfconnect/sdk-zephyr/blob/v3.2.99-ncs1/boards/arm/nrf5340dk_nrf5340/nrf5340_cpuapp_common-pinctrl.dtsi#L30

 

This will set the "skip_gpio_cfg" and tell the underlying driver that gpio(s) are already configured:

https://github.com/zephyrproject-rtos/hal_nordic/blob/f6628a30581d8d4b80954af163b83ce065e87467/nrfx/drivers/src/nrfx_uarte.c#L113

 

I2C lines and am wondering if I can enable the pull-up

Please note that you will be restricted to 100 kHz, as the internal pull up is too weak to drive any higher in open-drain mode. If you need 400 kHz, I would recommend that you use external pull-up of around 5k (4k7 for instance).

 

Kind regards,

Håkon

[nategreco]

Thanks - That's what I was looking for.

[Håkon Alseth]

Happy to help out.

Hope you have a wonderful day!

 

Cheers,

Håkon