AVR USART MSPIM vs. AVR SPI

The USART in MSPIM mode is fully compatible with the AVR SPI regarding:

However, since the USART in MSPIM mode reuses the USART resources, the use of the USART in MSPIM mode is somewhat different compared to the SPI. In addition to differences of the control register bits, and that only master operation is supported by the USART in MSPIM mode, the following features differ between the two modules:

A comparison of the USART in MSPIM mode and the SPI pins is shown in the table below.

Table 1. Comparison of USART in MSPIM mode and SPI pins
USART_MSPIM SPI Comments
TxDn MOSI Master Out only
RxDn MISO Master In only
XCKn SCK (Functionally identical)
(N/A) SS Not supported by USART in MSPIM