control register 1
| CPHA | Clock phase |
| CPOL | Clock polarity |
| MSTR | Master selection |
| BR | Baud rate control |
| SPE | SPI enable |
| LSBFIRST | Frame format |
| SSI | Internal slave select |
| SSM | Software slave management |
| RXONLY | Receive only |
| DFF | Data frame format |
| CRCNEXT | CRC transfer next |
| CRCEN | Hardware CRC calculation enable |
| BIDIOE | Output enable in bidirectional mode |
| BIDIMODE | Bidirectional data mode enable |