25.3.3.1.3.1 Frame Formats

The serial frame for the USART in Master SPI mode always contains eight Data bits. The Data bits can be configured to be transmitted with either the LSb or MSb first, by writing to the Data Order bit (UDORD) in the Control C register (USARTn.CTRLC).

SPI does not use Start, Stop, or Parity bits, so the transmission frame can only consist of the Data bits.