The USART on the SAM3U has the same features as previous products: modem capability, hardware handshaking capability, CTS and  RTS management, and others, and Microchip has added a new feature, which is SPI mode. It supports Master and Slave modes, the max frequency is MCK divided by four and the SPI modes 0, 1, 2 and 3 are supported. The table shows how the USART pin is shared to handle the SPI Master or SPI Slave signals. On the SAM3U, up to five different SPIs are available: one real SPI and four USARTs configured in SPI Mode.