The CA9557 is an 8-bit I²C/SMBus I/O expander designed to provide remote GPIO expansion for a wide range of MCU-based systems. It includes input, output, configuration, and polarity-inversion registers, allowing each I/O pin to be individually programmed as an input or output. At power-up, all eight pins default to inputs, and their behavior can be reconfigured through the I²C/SMBus interface.

The device offers low standby current, 5 V tolerant I/Os, and a high-impedance open-drain output on P0, which is suitable for signalling or wired-OR applications. A power-on reset ensures stable initialization, while the active-low RESET pin enables system recovery in the event of timeouts or communication errors. With support for up to eight address combinations and I²C speeds up to 400 kHz, the CA9557 is a reliable solution for server, notebook and telecom applications.