The MCP23S17-E/SO device provides 16 bit, general purpose parallel I/O expansion for I2C bus or SPI applications. The device has an I2C interface. The MCP23S17-E/SO consists of multiple 8 bit configuration registers for input, output and polarity selection. The system master can enable the I/Os as either inputs or outputs by writing the I/O configuration bits (IODIRA/B). The data for each input or output is kept in the corresponding input or output register. The polarity of the Input Port register can be inverted with the Polarity Inversion register. All registers can be read by the system master. The 16 bit I/O port functionally consists of two 8 bit ports (PORTA and PORTB). The MCP23S17-E/SO can be configured to operate in the 8 bit or 16 bit modes via IOCON.BANK.