The MCP23017-E/SS is a 16-bit I/O Expander provides general purpose parallel I/O expansion for I²C bus or SPI applications. The two devices differ only in the serial interface. It 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 I