UART status register
| RXFIFO_CNT | Stores the byte number of valid data in Rx-FIFO. |
| DSRN | The register represent the level value of the internal uart dsr signal. |
| CTSN | This register represent the level value of the internal uart cts signal. |
| RXD | This register represent the level value of the internal uart rxd signal. |
| TXFIFO_CNT | Stores the byte number of data in Tx-FIFO. |
| DTRN | This bit represents the level of the internal uart dtr signal. |
| RTSN | This bit represents the level of the internal uart rts signal. |
| TXD | This bit represents the level of the internal uart txd signal. |