8-bit I²C I/O expander — what it does and where it fits
The PCA9534DWR is an 8-bit I/O expander from Texas Instruments that connects to a host controller over the I²C or SMBus interface, adding eight general-purpose I/O pins to a system that has run out of GPIO on the main MCU or SoC. Each I/O pin can sink up to 25 mA or source 10 mA, enough to drive LEDs directly or interface with small relays through a transistor buffer, and the push-pull output structure eliminates the need for external pull-up resistors on the output side.
I/O count, interrupt, and POR — the features that matter on the bench
The eight I/O pins are individually configurable as inputs or outputs, and the device includes a power-on reset (POR) circuit that initialises all registers to a known state when the supply crosses the threshold, eliminating the need for a manual reset pin. An open-drain interrupt output (INT) asserts when any input pin changes state, allowing the host to avoid continuous I²C polling and instead wake from a low-power mode only when a change is detected — useful for keypad scanning or sensor monitoring.