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

[Håkon Alseth]

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

[Lasto]

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

[kpTTT]

both of these links seem to be expired, as of sdk version 2.4.0, is there any way to set bias-pull-up for i2c?

[Håkon Alseth]

Syntax hasn't changed for newer versions of ncs. You can address this in pinctrl DT with for instance "bias-pull-up;"

[kpTTT]

i add it to my group like the commented out section //bias-pull-up; above and it does nothing. my ide says that Property [bias-pull-up;] not mentioned in "nordic,nrf-pinctrl:child:child"

[Håkon Alseth]

Hi,

 

You are re-using the same names that are originally defined in the board itself.

To override that, you need to follow the exact same layout in terms of groups etc.

 

It is usually easier to define your own pinctrl instance (you can name them whatever you want):

&pinctrl {
	new_pinctrl_default: new_pinctrl_default {
		group1 {
			psels = <NRF_PSEL(TWIM_SDA, 0, 26)>,
				<NRF_PSEL(TWIM_SCL, 0, 27)>;
		};
	};

	new_pinctrl_sleep: new_pinctrl_sleep {
		group1 {
			psels = <NRF_PSEL(TWIM_SDA, 0, 26)>,
				<NRF_PSEL(TWIM_SCL, 0, 27)>;
			low-power-enable;
		};
	};    
};

&i2c0 {
    ...
	pinctrl-0 = <&new_pinctrl_default>;
	pinctrl-1 = <&new_pinctrl_sleep>;
	pinctrl-names = "default", "sleep";
};

 

Here you can add your own configurations.

 

Kind regards,

Håkon