If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
It looks like you are attempting to read the 0x01 register which is the input port 1 register. This should read 0xFF since TCA9555 implements 100k pull-ups on each of the IO's.
To read the polarity inversion register, i think you are wanting to read 0x04 or 0x05.
