To support both buses – I2C and SPI and to minimize the number of pins, most of the pins are shared between the two bus configurations. This slide here helps to see the exact pin map for each of the bus. The lower half of the table list the shared pins and how they are mapped depends on the state of the I2C/-SPI pin. When configured as I2C, the pin A0, A1 pin can be used to set the SC16IS7xx I2C slave address, and up to 16 addresses can be selected.