Interrupt status register. Reflects interrupts that are currently enabled.
| TXIDLE | Transmitter Idle status. |
| DELTACTS | This bit is set when a change in the state of the CTS input is detected. |
| TXDISINT | Transmitter Disabled Interrupt flag. |
| DELTARXBRK | This bit is set when a change in the state of receiver break detection occurs. |
| START | This bit is set when a start is detected on the receiver input. |
| FRAMERRINT | Framing Error interrupt flag. |
| PARITYERRINT | Parity Error interrupt flag. |
| RXNOISEINT | Received Noise interrupt flag. |
| ABERRINT | Auto baud Error Interrupt flag. |