Hello,

I am trying to communicate with TDA8375 over I2C1 with 100khz speed. i2cdetect -y 1 detects all the addresses including TDA8375, it can read and write all addresses expect TDA8375. However when I try with I2C3 I am able to read and write to TDA8375.

I have bus pirate connected same I2C line and it can read and write to all addresses. R/W to TDA8375 fails because of the missing ACK from the slave device. Since I am using I2C3 for different purpose, I need to figure out why I2C1 is failing.

The I2C network that I am trying to hack has its own master and it is 5V logic. I am using bi-directional logic level shifters (BSS138) to connect RPI, bus pirate connected to 5V logic with pull up resistors enabled. What can be the reason for the read/write error? (I tried increasing and decreasing I2C clock frequency). Build in pull-up resistors of I2C1?

Many thanks

Yes, I2C1 on GPIOs 2 & 3 has onboard pull-ups. If something else is also pulling-up the bus, your TDA8375 may be having difficulty overcoming the combined pull.