Control register 3
| EIE | Error interrupt enable |
| IREN | IrDA mode enable |
| IRLP | IrDA low-power |
| HDSEL | Half-duplex selection |
| NACK | Smartcard NACK enable |
| SCEN | Smartcard mode enable |
| DMAR | DMA enable receiver |
| DMAT | DMA enable transmitter |
| RTSE | RTS enable |
| CTSE | CTS enable |
| CTSIE | CTS interrupt enable |
| ONEBIT | One sample bit method enable |