Status Register
| RDRF | Receive Data Register Full (cleared by reading SPI_RDR) |
| TDRE | Transmit Data Register Empty (cleared by writing SPI_TDR) |
| TXEMPTY | Transmission Registers Empty (cleared by writing SPI_TDR) |
| OVRES | Overrun Error Status (cleared on read) |
| CSR | Chip Select Rise (cleared on read) |
| CSS | Chip Select Status |
| INSTRE | Instruction End Status (cleared on read) |
| QSPIENS | QSPI Enable Status |