UART status register
| RXFIFO_CNT | Stores the number of valid data bytes in RX FIFO. |
| DSRN | This register represents the level of the internal UART DSR signal. |
| CTSN | This register represents the level of the internal UART CTS signal. |
| RXD | This register represents the level of the internal UART RXD signal. |
| TXFIFO_CNT | Stores the number of data bytes 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. |