资 源 简 介
The PCA9554 and PCA9554A are 16-pin CMOS devices that provide 8 bits of GeneralPurpose parallel Input/Output (GPIO) expansion for I2C-bus/SMBus applicaTIons andwere developed to enhance the NXP Semiconductors family of I2C-bus I/O expanders.The improvements include higher drive capability, 5 V I/O tolerance, lower supply current,individual I/O configuraTIon, 400 kHz clock frequency, and smaller packaging. I/Oexpanders provide a simple soluTIon when addiTIonal I/O is needed for ACPI powerswitches, sensors, push buttons, LEDs, fans, etc.The PCA9554/PCA9554A consist of an 8-bit Configuration register (Input or Outputselection); 8-bit Input Port register, 8-bit Output Port register and an 8-bit PolarityInversion register (active HIGH or active LOW operation). The system master can enablethe I/Os as either inputs or outputs by writing to the I/O configuration bits. The data foreach input or output is kept in the corresponding Input Port or Output Port register. Thepolarity of the read register can be inverted with the Polarity Inversion register. Allregisters can be read by the system master. Although pin-to-pin and I2C-bus addresscompatible with the PCF8574 series, software changes are required due to theenhancements and are discussed in Application Note AN469.The PCA9554/PCA9554A open-drain interrupt output is activated when any input statediffers from its corresponding Input Port register state and is used to indicate to thesystem master that an input state has changed. The power-on reset sets the registers totheir default values and initializes the device state machine.Three hardware pins (A0, A1, A2) vary the fixed I2C-bus address and allow up to eightdevices to share the same I2C-bus/SMBus. The PCA9554A is identical to the PCA9554except that the fixed I2C-bus address is different allowing up to sixteen of these devices(eight of each) on the same I2C-bus/SMBus.
