We uses TCA6408A at below condition,
1. Polarity Inversion Register ： 0x0F (P[3:0] are inverted)
2. Configuration Register : 0xFF (All ports are input)
At first, we confirmed that appropriate function by toggling P3, observed xINT and correct input registers.
But when we toggling P0, we observed strange phenomena. We can not observed xINT and Polarity Inversion Register is reset.
Sequence is below,
Input Port Register ： 0x00
Output Port Register ： 0xFF
Polarity Inversion Register ： 0x0F
Configuration Register ： 0xFF
Turn P0 H to L, we do NOT observe xINT
Turn P0 L to H, we do observe xINT.
Read out register value after turn P0 L to H is below
Input Port Register ： 0x0F
Output Port Register ： 0xFF
Polarity Inversion Register ： 0x00
Configuration Register ： 0xFF
It seems only the Polarity Inversion Register is reset.
We tried with Configuration Register is eq to 0x0F, but this register would not reset. So we do not think the TCA6408A device reset.
Could you tell us know possible reason why not observe xINT by turn only P0 turn H to L?
