RE: TWI read is not happening

madblue — Tue, 27 Mar 2018 16:19:53 GMT

Thanks for the reply Martin,

I am using max30205

your understanding of the logic trace is correct, but only the first write is happening properly. after that if i try to read or write, its not coming

void twi_init (void)
{
    ret_code_t err_code;

    const nrf_drv_twi_config_t twi_lm75b_config = {
       .scl                = MLX_CLOCK_PIN,
       .sda                = MLX_DATA_PIN,
       .frequency          = NRF_TWI_FREQ_400K,
       .interrupt_priority = APP_IRQ_PRIORITY_HIGH,
       .clear_bus_init     = false
    };

    err_code = nrf_drv_twi_init(&m_twi, &twi_lm75b_config, twi_handler, NULL);
    APP_ERROR_CHECK(err_code);

    nrf_drv_twi_enable(&m_twi);
}

TWI Read

uint8_t reg[1] = {0 };

nrf_drv_twi_tx(&m_twi, MAX30205_SENSOR_ADDR, reg, sizeof(reg), false);
while (m_xfer_done == false);

err_code = nrf_drv_twi_rx(&m_twi, MAX30205_SENSOR_ADDR, m_sample, 2);
APP_ERROR_CHECK(err_code);

RE: TWI read is not happening

MartinBL — Tue, 27 Mar 2018 12:02:46 GMT

Hi,

Can you post the code showing how you perform you reads and writes?
What TWI slave are you using?
I don't see what is wrong in your logic traces. The green dots are start conditions, and the brown dots are stop conditions. In your first image it looks like you try to read from register 0 by writing a byte with value 0, which the slave ACKs, and then start a TWI read operation where the slave responds with value 0x1F.