Serial Control Register
| TXE | Data transmission enable bit |
| RXE | Data received enable bit |
| TBIE | Transmit bus idle interrupt enable bit |
| TIE | Transmit interrupt enable bit |
| RIE | Received interrupt enable bit |
| SPI | SPI corresponding bit |
| MS | Master/Slave function select bit |
| UPCL | Programmable clear bit |