8-bit SPI GPIO expander in a through-hole DIP
The Microchip MCP23S09-E/P is an 8-bit I/O expander controlled via an SPI interface, providing eight additional GPIO pins to a host microcontroller through a simple serial bus.
Open-drain outputs and interrupt — wired-OR ready
All eight I/O pins are configured as open-drain outputs, each capable of sinking or sourcing 25 mA. Open-drain outputs let multiple expanders or other open-drain devices share a common bus line without contention — useful for wired-OR interrupt signaling or driving LEDs with a shared pull-up. The part includes a dedicated interrupt output pin (INTA) that asserts when an input pin changes state, allowing the host MCU to poll only on demand rather than continuously scanning the SPI bus.
10 MHz SPI bus — timing margin for most MCUs
The SPI interface runs at up to 10 MHz. The 18-pin DIP package keeps trace lengths short for signal integrity on a breadboard or two-layer PCB.
It is ROHS3 compliant.