TWI SDA SCL held low during reset when using TWIS

[pavel.kucera]

Hi to community!

I have a trouble with nRF52840 when using TWIS. I initialize the peripheral by below code. If the device is reset using default pin 18 by the external controller, SDA and SCL pins are held low, so the communication with other sensors on bus is broken. Is there a way for the mentioned signals to be in Hi-Z during reset? 

nrf_gpio_cfg(26U, NRF_GPIO_PIN_DIR_INPUT, NRF_GPIO_PIN_INPUT_CONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_S0D1, NRF_GPIO_PIN_NOSENSE);
nrf_gpio_cfg(27U, NRF_GPIO_PIN_DIR_INPUT, NRF_GPIO_PIN_INPUT_CONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_S0D1, NRF_GPIO_PIN_NOSENSE);
const nrf_drv_twis_config_t config =
{
  .addr = {0x0BU, 0U},
  .scl = 27U,
  .sda = 26U,
  .scl_pull = NRF_GPIO_PIN_PULLUP,
  .sda_pull = NRF_GPIO_PIN_PULLUP,
  .interrupt_priority = APP_IRQ_PRIORITY_HIGH
};
nrf_drv_twis_init(&f_i2c, &config, i2c_event_handler);

It behaves in same way if the first two lines (nrf_gpio_cfg) are omitted.

Thank in advance for any help with this problem.

[pavel.kucera]

From my point of view this discussion leads to nowhere. Could you please guide me to the documentation, where one could read that pin states are undefined during reset? So I can tell that to customer, it is not my fault as a FW programmer, that those pins are low during reset?

[Vidar Berg]

 Sorry. But are you able to use workaround you already suggested? As I indicated earlier, the pin state is not defined in reset. The documented reset values applies to when the internal reset sequence is completed (ie after you release the reset line).  Although, I do understand it might be surprising that the pins become configured as outputs in this case.