The PCA8575DB is a 16-bit I2C I/O expander from NXP in SSOP-24. It provides 16 quasi-bidirectional I/O pins organized as two 8-bit ports (P00-P07, P10-P17), controlled via a standard 400kHz I2C interface. Quasi-bidirectional I/O pins can function as both input and output without a direction control register: each pin has a weak internal pull-up current source (approximately 100uA) that drives the pin HIGH, and an external device can override this by pulling the pin LOW. To write outputs, the master sends the I2C slave address followed by two data bytes (Port 0, Port 1). To read inputs, the master sends the address with the read bit, and the PCA8575 returns the current pin states. The INT pin generates an active-low interrupt whenever any input pin changes state (compared to the previous read), enabling event-driven polling instead of continuous I2C reads. The three address pins (A0-A2) allow up to 8 devices on the same I2C bus, providing up to 128 I/O channels. Typical applications include expanding MCU I/O for keyboards, LED drivers, and sensor interfaces.