Use UART, but make the TX pin open drain.

[Jordan Archer]

It is possible to switch the TX pin to open drain, when the UART is enabled on an nrf53?

My goal is to use the uart as a 1 wire interface, 

[run_ar]

Since we do not have a one wire implementation I would suggest you look at the third party implementation suggested in this thread: https://devzone.nordicsemi.com/f/nordic-q-a/30474/nrf52-dallas-slave-1-wire-with-bt

It is written for nRF51 originaly, but it should run on the nRF52 as well.

[Jordan Archer]

You missed the original question.  Can I make the uart device, with the TX pin being open drain?

[hmolesworth]

Ah, I see. Try adding this function in SDKv1.5.1 uart_nrfx_uarte.c:

NRF_STATIC_INLINE void cfg_tx_pin(uint32_t pin_number)
{
    nrf_gpio_cfg(
        pin_number,
        NRF_GPIO_PIN_DIR_OUTPUT,
        NRF_GPIO_PIN_INPUT_CONNECT,  // Connect for single pix tx/rx
        NRF_GPIO_PIN_PULLUP, // If not using external pull-up
        NRF_GPIO_PIN_H0D1,  // Open drain
        NRF_GPIO_PIN_NOSENSE);
}

Then change this around line 1424 in uart_nrfx_uarte.c:

	nrf_gpio_pin_write(config->pseltxd, 1);
	nrf_gpio_cfg_output(config->pseltxd);

to this:

	nrf_gpio_pin_write(config->pseltxd, 1);
	cfg_tx_pin(config->pseltxd);

[Jordan Archer]

OK, thanks!

[hmolesworth]

I edited my response above to show input connected; assuming you are wanting to use a single pin for both Tx and Rx. Let us know if you have it working ok - thanks