Status Register
| RDRF | Receive Data Register Full (cleared by reading SPI_RDR) |
| TDRE | Transmit Data Register Empty (cleared by writing SPI_TDR) |
| MODF | Mode Fault Error (cleared on read) |
| OVRES | Overrun Error Status (cleared on read) |
| NSSR | NSS Rising (cleared on read) |
| TXEMPTY | Transmission Registers Empty (cleared by writing SPI_TDR) |
| UNDES | Underrun Error Status (Slave mode only) (cleared on read) |
| SPIENS | SPI Enable Status |