When a character reception is completed, it is transferred to US_RHR and US_CSR.RXRDY rises. If a character is completed while RXRDY is set, the OVRE (Overrun Error) bit is set. The last character is transferred into US_RHR and overwrites the previous one. The OVRE bit is cleared by writing a ‘1’ to US_CR.RSTSTA.
To ensure correct behavior of the receiver in SPI Slave mode, the master device sending the frame must ensure a minimum delay of one tbit between each character transmission. The receiver does not require a falling edge of the slave select line (NSS) to initiate a character reception but only a low level. However, this low level must be present on the slave select line (NSS) at least one tbit before the first serial clock cycle corresponding to the MSB bit.