The TCA9536 has a combination P3 and INT output pin. The function of the pin is selected by the special function register. When the pin is configured as an INT output, the internal-pull up resistor is enabled by default, but will depend on the state of the PU Disable bit in the special function register. See Table 8-7 for more information. The below text describes the functionality of the pin when configured as an INT output.

An interrupt is generated by any rising or falling edge of the port inputs in the input mode. After time t_iv, the signal INT is valid. Resetting the interrupt circuit is achieved when data on the port is changed to the original setting or data is read from the port that generated the interrupt. Resetting occurs in the read mode at the acknowledge (ACK) bit after the rising edge of the SCL signal. Note that the INT is reset at the ACK just before the byte of changed data is sent. Interrupts that occur during the ACK clock pulse can be lost (or be very short) because of the resetting of the interrupt during this pulse. Each change of the I/Os after resetting is detected and is transmitted as INT.

Reading from or writing to another device does not affect the interrupt circuit, and a pin configured as an output cannot cause an interrupt. Changing an I/O from an output to an input may cause a false interrupt to occur if the state of the pin does not match the contents of the Input Port register.

INT has an open-drain structure and requires a pull-up resistor to V_CC of moderate value (typically about 10 kΩ).