Advantech ITA-3630 Series User Manual page 63

PCA9554 register 2:
If one GPIO Pin is set to Input, you can control the polarity of input pin from the bit
that register 2 corresponds to.
PCA9554 register 3:
Register 3 is used to set each GPIO as Input or Output:
If the bit is '0', the corresponding GPIO pin is set as Ouput;
If the bit is '1', the corresponding GPIO pin is set as Input.
53 ITA-3630 User Manual