sht21 with nrf51822 measuring temperature

[talha]

Hi,

I am trying to measure the temperature using sht21 sensor with nrf51822. I am using TWI to do this. When I try to send a data to the sensor the application cannot do that. The code for initializing and measuring the temperature is as follows:

static void twi_master_init(void)
{
ret_code_t ret_code;
//Setup SDA and SCL pin, twi frequency and interrupt priority
const nrf_drv_twi_config_t config =
{
   .scl                = 18, 
   .sda                = 17, 
   .frequency          = NRF_TWI_FREQ_100K,
   .interrupt_priority = APP_IRQ_PRIORITY_HIGH
};

do
{
    // Unncommend line below to setup TWI without an event handler
    //ret_code = nrf_drv_twi_init(&twiMaster, &config, NULL); 
    // Setup TWI with an event handler  
    ret_code = nrf_drv_twi_init(&twiMaster, &config, NULL, NULL);    
    if(ret_code!= NRF_SUCCESS)
    {
        break;
    }
    nrf_drv_twi_enable(&twiMaster);
}while(0);
 }

static void measureTemperature( int* temperature )
 {
ret_code_t err_code;
uint8_t command_address[1] = {0xF3U};
uint8_t read[2] = {0x0000U};

err_code = nrf_drv_twi_tx( &twiMaster, DEVICE_ADDRESS, command_address, sizeof(command_address), false);
SEGGER_RTT_printf(0, "variable value: %d\n", err_code);
//APP_ERROR_CHECK(err_code);

nrf_delay_ms(200);
nrf_drv_twi_rx( &twiMaster, DEVICE_ADDRESS, read, sizeof(read));

*temperature = ROUNDED_DIV( ((21965 * (*read)) >> 13) - 46850, 1000 );

   }

If I uncomment the line "APP_ERROR_CHECK(err_code);" the application crashes. Otherwise the Segger RTT shows that err_code is equal to 3.

What does this mean? How can I solve this error? Any help is appreciated.

Thanks in advance.

Edit: I dig in the code a little bit and found that err_code = 3 means that it is NRF_ERROR_INTERNAL. I have no idea what it means though.

Edit2: I was trying to debug the code by using a twi_event_handler. I noticed that the sht21 is giving ADRESS_NACK error. So the address is not acknowledged by the sht21. I am pretty sure the adress part of the code is correct though?

Edit3: Ok the problem is solved. The datasheet provided for my custom board was mistakenly written the .sda and .scl pins. I verified the correct pins and now it is working.

Thanks

[Susheel Nuguru]

This error is generated in nrf_drv_twi.c->twim_xfer where the actual transfer of the data is placed into the hardware.

The documentation for the API nrf_drv_twi_tx shows that

@retval NRF_ERROR_INTERNAL If an error was detected by hardware.

This means that the the function has finished what it supposed to do what there were errors detected in TWI->ERRSRC module. Most probably this is an overrun error which means that you are not reading the data fast enough. The previous data in in RXD register was overwritten.