NAU7802 and I2C Clock Problem

Sensors Force & Weight
1

I am using the NAU7802 breakout board with a PIC18F4525 microcontroller. The I2C bus has an TXS0104E level translator and the NAU7802 on it. When I try to communicate with the NAU7802 the Start is asserted and after two clock pulses the clock goes to ZERO and stays there. If I remove the NAU7802 and send the same communication the messages are correct. I am using a logic analyzer to verify this. I am using the hardware I2C of the PIC and the MCC18 compiler.

I thought maybe the 2.2k pullups and the internal 10k pullups resulted in too low resistance so I replaced the 2.2k resistors with 10k so there is 5k of pullup now on the bus. It still does not work. My code is giving plenty of time for the NAU7802 to wake up. If I don’t enable the TXS0104E and have just the NAU7802 on the bus it still does not work. It works fine with the 10k pullups of the TXS0104E and NO NAU7802 connected.

I am out of ideas. Could the part on the breakout board be bad? That seems unlikely. I have 40 years of electronic design experience so I think I know what I am doing, even though my specialty is high power RF. This is my first attempt at using I2C but I have used SPI and written plenty of code for that.

Thanks in advance.

2

I fixed my problem by removing series resistors in the SDA and SCL lines. They were there in my circuit from a SPI configuration I had.

Know my problem is that the NAU7802 returns NACK instead of ACK, at least that is what my logic analyzer tells me. When I read back register 0x00 I get 0xFF which is another indication that the device is not responding.

Any ideas?