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??

[Ole Bauck]

This should do it (includes the setup):

//global variables
static uint8_t data[2] = {0x2D, 8};    //contains register + data to be written to register
#define ADXL345_ADDR        0x53U

//local code
uint32_t ret_code;
static const nrf_drv_twi_t           p_twi_instance = NRF_DRV_TWI_INSTANCE(0);

const nrf_drv_twi_config_t p_twi_config = {
   .scl                = SCL_PIN,
   .sda                = SDA_PIN,
   .frequency          = NRF_TWI_FREQ_400K,
   .interrupt_priority = APP_IRQ_PRIORITY_LOW
};

//Initiate twi driver with instance and configuration values
ret_code = nrf_drv_twi_init(&p_twi_instance, &p_twi_config, twi_handler, NULL); 
APP_ERROR_CHECK(ret_code); // Check for errors in return value

nrf_drv_twi_enable(&p_twi_instance); // Enable the TWI instance

ret_code = nrf_drv_twi_tx(&p_twi_instance, ADXL345_ADDR, data, sizeof(data), false);

[Ole Bauck]

The twi handler will be called when the transfer is done or an error condition is met (e.g. NACK recevied).

void twi_handler(nrf_drv_twi_evt_t const * p_event, void * p_context)
{   
    switch(p_event->type)
    {
        case NRF_DRV_TWI_RX_DONE:
            //code to be run when RX done (nrf_drv_twi_rx done)
            //For example check the data that was received
            break;
        case NRF_DRV_TWI_TX_DONE:
            //code to be run when TX done (nrf_drv_twi_tx done)
            //For example start reading register if this was sent with nrf_drv_twi_tx
            //with xfer pending equals true
            break;
        default:
            break;        
    }   
}