nRF52-DK / TWI does not send anything

[Sami]

I have some problems with the TWI (I2C) and it seems that TWI1 does not send anything. I have managed to create a simple example to recreate the issue. I am using TWI1 instead of TWI0, because I will need the other instance ID for the UART. I am using SES + nRF5 16.0.0 + nRF52-DK.

I am using the leds of the board to debug the issue. Leds 1 and 2 are turned on, but the program never receives event TXDSENT. When I look at the bus with a logic analyzer, there is no traffic at all. However, it seems that the bus is initialized correctly, because both the SCL and SDA (pins 9 and 10) are set high when the board is booted. I have also noticed that there is not even a start condition on the bus. Both the SCL and the SDA remain high.

Do you know what might be wrong?

#include <stdint.h>
#include <string.h>

#include "nrf_delay.h"
#include "nrf.h"
#include "nrf_gpio.h"

#define LED_1 17
#define LED_2 18
#define LED_3 19
#define LED_4 20

#define LED_ON  0
#define LED_OFF 1

#define I2C_SCL_PIN  9
#define I2C_SDA_PIN 10

void led_init (void)
{
    nrf_gpio_range_cfg_output(LED_1,LED_4);

    nrf_gpio_pin_write(LED_1,LED_OFF);
    nrf_gpio_pin_write(LED_2,LED_OFF);
    nrf_gpio_pin_write(LED_3,LED_OFF);
    nrf_gpio_pin_write(LED_4,LED_OFF);
}

void led (uint8_t led_id,uint8_t state)
{
    nrf_gpio_pin_write(led_id,state);
}

void i2c_init (void)
{
    NRF_TWI1->FREQUENCY = 0x01980000;     // 100 KHz

    NRF_TWI1->PSELSCL   = I2C_SCL_PIN;    // Pin  9, this is not a mask register!
    NRF_TWI1->PSELSDA   = I2C_SDA_PIN;    // Pin 10, this is not a mask register!
    
    NRF_TWI1->ADDRESS   = 0x40;           // Without read/write bit!

    NRF_TWI1->ENABLE    = 0x00000005;     // Enable
}

int main (void)
{
    led_init();
    i2c_init();

    led(LED_1,LED_ON);   // Debug LED 1

    NRF_TWI1->TASKS_STARTTX = 1;

    NRF_TWI1->TXD = 0xFE;

    led(LED_2,LED_ON);   // Debug LED 2

    while (NRF_TWI1->EVENTS_TXDSENT == 0)  { }

    NRF_TWI1->EVENTS_TXDSENT = 0;

    return 0;
}

[Sami]

I have also tested to set the pins manually in the beginning of i2c_init(). I have tried both with and without internal pullup resistors. The board has been connected to a digital temperature sensor (I2C). The temperature sensor has also pullup resistors (10K).

nrf_gpio_cfg_input(I2C_SCL_PIN,NRF_GPIO_PIN_PULLUP);
nrf_gpio_cfg_input(I2C_SDA_PIN,NRF_GPIO_PIN_PULLUP); 

nrf_gpio_cfg_input(I2C_SCL_PIN,NRF_GPIO_PIN_NOPULL); 
nrf_gpio_cfg_input(I2C_SDA_PIN,NRF_GPIO_PIN_NOPULL);