The PCA9555 functional block diagram (datasheet figure 18) indicates there is an internal 100K pull up resistor on each I/O, causing an IO when configured as input to be pulled high.
The application diagram figure 29 on page 24 suggests that a switch can be connected using an external pull up resistor to Vcc, which would require that an input is at a logic low when floating, not an internal pull up of 100K to Vcc.
Which one of the two diagrams is correct?
Do the IO's have internal pull up resistors, in that case the external switch topology will not work.
Pls. confirm which one is correct.