Control register 3
| ERRIEN | Error interrupt enable |
| IRDAEN | IrDA enable |
| IRDALP | IrDA low-power mode |
| SLBEN | Single line bidirectional half-duplex enable |
| SCNACKEN | Smartcard NACK enable |
| SCMEN | Smartcard mode enable |
| DMAREN | DMA receiver enable |
| DMATEN | DMA transmitter enable |
| RTSEN | RTS enable |
| CTSEN | CTS enable |
| CTSCFIEN | CTSCF interrupt enable |
| SMUSEN | Deepsleep mode usart enable |
| LPWUFIE | Low power wakeup flag interrupt enable |
| RS485EN | RS485 enable |
| DEP | DE polarity selection |
| LPWUM | Low power wakeup method |