Receiver interrupt mask
| TRIGGER | Mask bit for corresponding bit in interrupt request register. |
| NOT_EMPTY | Mask bit for corresponding bit in interrupt request register. |
| FULL | Mask bit for corresponding bit in interrupt request register. |
| OVERFLOW | Mask bit for corresponding bit in interrupt request register. |
| UNDERFLOW | Mask bit for corresponding bit in interrupt request register. |
| BLOCKED | Mask bit for corresponding bit in interrupt request register. |
| FRAME_ERROR | Mask bit for corresponding bit in interrupt request register. |
| PARITY_ERROR | Mask bit for corresponding bit in interrupt request register. |
| BAUD_DETECT | Mask bit for corresponding bit in interrupt request register. |
| BREAK_DETECT | Mask bit for corresponding bit in interrupt request register. |