Enabling Internal Pull-Up Resistors for I2C Lines nRF5340

[Paul M.]

Hello everyone,

I am working with the nRF5340 and use several sensors using the I2C communication. 

I've read in the product specification that there are internal pull up resistors of 13 kOhm on all GPIOs. How do I enable them?

Thanks in advance,

Morandell Paul

[Vidar Berg]

Hello,

You can enable pull-up on the I2C lines by adding the 'bias-pull-up' property to your i2c pin assignments in the device tree.

e.g.

...
&pinctrl {
	i2c1_default: i2c1_default {
		group1 {
			psels = <NRF_PSEL(TWIM_SDA, 1, 2)>,
				<NRF_PSEL(TWIM_SCL, 1, 3)>;
			bias-pull-up;
		};
	};

	i2c1_sleep: i2c1_sleep {
		group1 {
			psels = <NRF_PSEL(TWIM_SDA, 1, 2)>,
				<NRF_PSEL(TWIM_SCL, 1, 3)>;
			low-power-enable;
		};
	};
...

Best regards,

Vidar

[Paul M.]

Hello Vidar,

Thanks for the answer! How is it generally possible to configure pull ups and pull downs at the gpios? I have seen that there exist corresponding flags, however I do not understand where to set those flags. Could you give me a code example?

Thanks very much,

aul

[Vidar Berg]

Hello Paul,

GPIOs assigned to peripherals such as I2C are not directly configurable from the application, instead they are configured via the "Pin control" module with pin assignments from the device tree. Lesson 3 and 6 in our devacademy here: https://academy.nordicsemi.com/lessons/lesson-6-serial-com-i2c/ may help you make more sense of this.

Best regards,

Vidar

[Paul M.]

Ah I see, so it is not possible to switch the pull up of the I2C lines off again in the application?

[Vidar Berg]

The idea is that you let the pin control module handle the pin configuration for you based on the description from your device tree. This is one of the things that helps make Zephyr projects compatible across different MCU vendors. But there isn't anything in the SDK that will prevent you from accessing the GPIO configuration register and changing the pull-up configuration yourself. 

If you want, you can include <hal/nrf_gpio.h> in your project and use the HAL directly.

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfx/drivers/gpio/hal.html