PCA9555

  The PCA9555 is a 24-pin CMOS device that provide 16 bits of General Purpose parallel Input/Output (GPIO) expansion for I²C/SMBus applications ofPCA9555 and was developed to enhance the Philips family of IC I/O expanders. The improvements include higher drive capability, 5 V I/O tolerance, lower supply current, individual I/O configuration, and smaller packaging. I/O expanders provide a simple solution when additional I/O is needed for ACPI power switches, sensors, pushbuttons, LEDs, fans, etc.

   The PCA9555 consist of two 8-bit Configuration (Input or Output election); Input, Output and Polarity inversion (Active-HIGH or Active-LOW operation) registers. The system master can enable the /Os as either inputs or outputs by writing to the I/O configuration its. The data for each Input or Output is kept in the corresponding nput or Output register. The polarity of the read register of PCA9555 can be nverted with the Polarity Inversion Register.
    All registers of PCA9555 can be ead by the system master. Although pin-to-pin and I²C address ompatible with the PCF8575, software changes are required due to he enhancements and are discussed in  Application Note AN469.