The USI is a very high-performance serial interface with an 8- or 16-bit shift register that can be used to output data streams or, when combined with minimal software, can implement serial communication. In addition, the USI includes built-in hardware functionality to ease the implementation of SPI and I2C communication. The USI module also includes interrupts to further reduce the necessary software overhead for serial communication and to maintain the ultra low-power capabilities of the MSP430.