The PCA9555PW,118 is a 16-bit parallel Input/output (GPIO) Expander for I²C-bus/SMBus applications and was developed to enhance the NXP Semiconductors family of I²C-bus I/O expander. The improvements include higher drive capability, 5V I/O tolerance, lower supply current, individual I/O configuration and smaller packaging. The I/O expander provides a simple solution when additional I/O is needed for ACPI power switches, sensors, push buttons, LEDs, fans, etc. It consists of two 8-bit configuration (input or output selection); input, output and polarity inversion (active HIGH or active LOW operation) registers. The system master can enable the I/Os as either inputs or outputs by writing to the I/O configuration bits. The data for each Input or Output is kept in the corresponding Input or Output register. The polarity of the read register can be inverted with the polarity inversion register. All registers can be read by the system master.

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