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  • Case ID: 300966
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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

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  • 0

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

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    #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)
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    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`:

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    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);
    }
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    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

  • +1 in reply to nategreco

    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

Reply Children
  • 0 in reply to Håkon Alseth

    Thanks - That's what I was looking for.

  • 0 in reply to nategreco

    Happy to help out.

    Hope you have a wonderful day!

     

    Cheers,

    Håkon

  • 0 in reply to Håkon Alseth

    Hello,

    I'm running into issues accessing a sensor via i2c ("nordic,nrf-twim") and I just want to verify that the pull-up configuration is not the source of the issue. Is the following configuration OK?

    &pinctrl {
        i2c0_default: i2c0_default {
            group1 {
                psels = <NRF_PSEL(TWIM_SDA, 0, 2)>,
                    <NRF_PSEL(TWIM_SCL, 0, 5)>;
                // bias-disable;
                // bias-pull-up;
            };
        };
        i2c0_sleep: i2c0_sleep {
            group1 {
                psels = <NRF_PSEL(TWIM_SDA, 0, 2)>,
                    <NRF_PSEL(TWIM_SCL, 0, 5)>;
                // bias-disable;
                // bias-pull-up;
                low-power-enable;
            };
        };
    };

    &i2c0{
        compatible = "nordic,nrf-twim";
        status = "okay";
        clock-frequency = <I2C_BITRATE_STANDARD>;

        // Use pin control to specify SDA and SCL pin
        pinctrl-0 = <&i2c0_default>;
        pinctrl-1 = <&i2c0_sleep>;
        pinctrl-names = "default", "sleep";

        lis2dh120:lis2dh@19{    
            compatible = "st,lis2dh","st,lis2dh12";
            reg = <0x19>;
            vin-supply = < &lis2dh_pwr >; // fixed regulator node
            irq-gpios = <&gpio0 6 GPIO_ACTIVE_HIGH>, // INT1
                        <&gpio0 7 GPIO_ACTIVE_HIGH>; // INT2
            // disconnect-sdo-sa0-pull-up;
            status = "okay";
        };
    };

    Which is using GPIO0.2 and GPIO0.5 as SDA and SCL on nRF52810. I tried both with and without "bias-pull-up".

    The issue is described in more details in regulator-powered sensor fails to acknowledge over i2c after replacing battery

    Thank you.

  • 0 in reply to Lasto

    Hi,

     

    I would recommend that you continue in the thread that you linked to. Use a logic analyzer to see how the SDA/SCL lines behave when trying to communicate.

     

    Kind regards,

    Håkon

  • 0 in reply to Håkon Alseth

    Thank you. Will do both. I just wanted to verify that GPIO pull-up resistors' configurations are not the culprit.

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