Incorrect I2C Address

[ISN_B]

Hello,

I am testing out a custom board with the nRF52840 and I am trying to interface with an I2C slave using the chip. Right now I am just trying to see if I can find the slave using an I2C scanner, but no address is coming up. I have tested the I2C scanner with the development kit with the same sensor model and it can find the slave without any trouble. I made sure the connections were intact on the board, but when I probed the SDA pin on the custom board, I saw that the address that the chip was sending was not the correct address.

The left image is taken from the SDA pin on the custom board when trying to send the address 0x01 and the right image is taken from the SDA pin on the development kit when trying to send 0x01. Since I have not been able to simultaneously probe the SCL on the custom board, I am not sure exactly what address is being outputted, but is there a reason why the sent address would be so different?

[Kenneth]

Maybe you are mixing device address with register address? Typically sequence for read and write are shown here:
https://devzone.nordicsemi.com/f/nordic-q-a/87283/i2c-doesn-t-transmit-the-data-correctly/364701#364701 

Kenneth

[ISN_B]

I am using the twi scanner code from the sdk to detect the slave device address, but no device is found on the custom board. I have confirmed that the SDA and SCL pins defined in the code match with the pins that the slave is connected to on the board. The images shown are taken from the SDA pins as soon as the TWI scanner code is run, with the first (and captured) test address being 0x01.

At this point I am not yet trying to read or write from the slave, but to just see if the nrf52840 chip recognizes the slave. I believe this issue of the chip not recognizing the slave is due to this difference in the address the SDA line is supposed to send (right) and what is actually being sent (left). What could be causing this difference?

Thank you

[Kenneth]

If the twi scanner example is not able to detect any slave, it is likely an electrical issue of some sort, e.g. make sure that the sensor is powered properly and it's in i2c mode (some sensors support for instance both i2c and spi etc).

Kenneth