The PCA8574/74A provides general-purpose remote I/O expansion via the two-wire bidirectional I²C‑bus (serial clock (SCL), serial data (SDA)).

The devices consist of eight quasi-bidirectional ports, 400 kHz I²C‑bus interface, three hardware address inputs and interrupt output operating between 2.3 V and 5.5 V. The quasi-bidirectional port can be independently assigned as an input to monitor interrupt status or keypads, or as an output to activate indicator devices such as LEDs. The system master can read from the input port or write to the output port through a single register.

The low current consumption of 4.5 μA (typical, static) is great for mobile applications and the latched output ports have 25 mA high current sink drive capability for directly driving LEDs.

I²C‑bus to parallel port expander
400 kHz I²C‑bus interface (Fast-mode I²C‑bus)
Operating supply voltage 2.3 V to 5.5 V with 5.5 V tolerant I/Os held to VDD with 100 μA current source
8-bit remote I/O pins that default to inputs at power-up
Latched outputs with 25 mA sink capability for directly driving LEDs
Total package sink capability of 200 mA
Active LOW open-drain interrupt output
Eight programmable slave addresses using three address pins