36.2.4 LSb vs. MSb-First Operation

Typically, the SPI communication outputs the Most Significant bit first, but some devices or buses may not conform to this standard. In this case, the LSBF bit may be used to alter the order in which bits are shifted out during the data exchange. In both Host and Client mode, the LSBF bit controls whether data are shifted to the MSb or LSb first. Clearing the bit (default) configures the data to transfer to the MSb first, which conforms to traditional SPI operation, while setting the bit configures the data to transfer to the LSb first.