I2C in nrf51 SDK

[rushin]

I want to interface ADXl345 with nrf51 SDK. suppoose my device address is 0x53 and register address is 0x2D and i want to write value 8. now nordic i2c has function nrf_drv_twi_tx with attributes nrf_drv_twi_t const *const p_instance, uint8_t address, uint8_t const * p_data, uint32_t length, bool xfer_pending

now here my address is 0x53, length is 6. now can you tell me where to write register address? where to write data??

[rushin]

ok may be i am not getting data because of it

[Ole Bauck]

You need to wait for the transfer to finish before returning the data and the data array needs to be globally declared. For example the read data should be like this:

uint8_t tx_data[2];

uint16_t read_data(nrf_drv_twi_t const * const  m_twi_adxl_345,uint8_t i2cAddress, uint8_t reg) 
{

    uint32_t           err_code;
    uint8_t data[2] = {0, 0};
    uint8_t value;

    tx_done = false;
    //Use xfer_pending true for repeated start (no need to send start condition and address again)
    err_code = nrf_drv_twi_tx(m_twi_adxl_345,ADXL345_ADDR , data, sizeof(data), true);
    APP_ERROR_CHECK(err_code);
    
    while(tx_done == false);  //wait for TX transfer to be done
    rx_done = false;
    err_code =  nrf_drv_twi_rx(m_twi_adxl_345,ADXL345_ADDR,data,sizeof(data),false);
    APP_ERROR_CHECK(err_code);

    while(rx_done == false);  //wait for RX transfer to be done
    value = (data[0] << 8) | data[1];
    return value;
}

This is not efficient code as it busy-waits, but it should work. rx_done and tx_done should be set to true respectively in the twi_handler function.

[Ole Bauck]

If you pass NULL as event handler you can do it the way you do.

[rushin]

it means i don't require separate write function

[bjorn-spockeli]

Hi Rushin,

you can take a look at the driver I wrote for the ADXL375. Its for the nRF52 SDK, but the twi_driver API should be close to identical with that of the nRF51 SDK.

ADXL375_I2C.zip