8-bit I²C I/O expander in 16-SOIC
The Texas Instruments PCF8574DW is an 8-bit I/O expander that communicates over the I²C bus, giving a microcontroller eight extra push-pull I/O lines without adding more pins.
Output drive and interrupt
Each I/O pin can source 1 mA or sink 25 mA — enough to light a standard LED directly (with a series resistor) or drive a small relay coil through a transistor. An interrupt output (INT) is available, so the expander can alert the host MCU when an input changes without the MCU having to poll the I²C bus continuously. The POR (power-on reset) feature ensures the I/O pins start in a known high-impedance state after the supply comes up, preventing unintended glitches on connected loads.