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PCF8574A: How to Prevent Missing Interrupts on PCF8574A During I2C ACK Phase?

Nikita Naik
Prodigy 10 points
Part Number: PCF8574A
Other Parts Discussed in Thread: TCA9539, TCA8418E

Tool/software:

Question:

I'm using the PCF8574A I/O expander in a project and encountering an issue with its interrupt (INT) line. The device generates an interrupt on any rising or falling edge of the port inputs, but I've noticed that interrupts can be missed during the I2C read operation, specifically when the ACK is being sent. This seems to happen because the interrupt is reset during the acknowledge phase, and any I/O changes close to this time may not generate a new interrupt or may result in a very short pulse.

At power-on reset, all ports are set to input mode with an initial HIGH state. If any port pin is pulled LOW externally, the interrupt output becomes active (LOW), which is expected. However, the challenge is ensuring that no interrupts are missed during the ACK phase.

Is there a recommended strategy or workaround to prevent missing interrupts during the ACK phase when using the PCF8574A? Any insights or suggestions for handling this in firmware or hardware would be greatly appreciated.