Interrupt Status Flags.
| FRAMIS | FLAG for RX Frame Error Interrupt. |
| PARITYIS | FLAG for RX Parity Error interrupt. |
| OVERIS | FLAG for RX FIFO Overrun interrupt. |
| FFRXIS | FLAG for interrupt when RX FIFO reaches the number of bytes configured by the RXTHD field. |
| FFTXOIS | FLAG for interrupt when TX FIFO has only one byte remaining. |
| FFTXHIS | FLAG for interrupt when TX FIFO reaches half the number of bytes allowed in the fifo or less. |