TWI Scanner I2C address is 1 bit wrong

[StevenW807]

I'm using <TWI Scanner> example on nRF52 DK to find my sensor's address.

According to the sensor datasheet, the sensor's address is 0x21. However, <TWI Scanner> finds the address at 0x20. 

Any idea, please? 

[Einar Thorsrud]

Hi,

Some I2C slaves lets you select one of a few addresses by hooking some pin(s) to VDD or ground, so that could be the case. Which sensor are you using?

[StevenW807]

I'm using SDP31 pressure sensor. Its datasheet is here. 

According to page 4, section 3.3, my ADDR connects to GND. So its I2C address should be 0x21. But <TWI scanner> demo shows that the address is 0x20. 

Thanks, Einar! 

[Einar Thorsrud]

Then I am out of ideas. The whole TWI Scanner example is essentially just this for loop:

    for (address = 1; address <= TWI_ADDRESSES; address++)
    {
        err_code = nrf_drv_twi_rx(&m_twi, address, &sample_data, sizeof(sample_data));
        if (err_code == NRF_SUCCESS)
        {
            detected_device = true;
            NRF_LOG_INFO("TWI device detected at address 0x%x.", address);
        }
        NRF_LOG_FLUSH();
    }

As you can see, it prints the address (loop iteration #) of any device it is able to read from. It should not fail... If this is still a problem, perhaps you can use a logic analyzer to see how this looks on the TWI bus?