PSoCs are devices that incorporate a microcontroller, a logical gate array, and some analog peripherals. What makes them different than microcontrollers is that all the peripherals are separated from the microcontroller. They can function totally independent from one another.
This app note describes how to connect two digital peripherals without sacrificing any additional resources of the IC.
PSoC is configured as an I2C slave and SPI master. This is because it can receive data from an I2C master and send this data to an SPI slave device. Also, the data received over the MISO line is stored so that it can be read by the I2C master during the next I2C read.