Transmitter interrupt mask
| TRIGGER | Mask bit for corresponding bit in interrupt request register. |
| NOT_FULL | Mask bit for corresponding bit in interrupt request register. |
| EMPTY | 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. |
| UART_NACK | Mask bit for corresponding bit in interrupt request register. |
| UART_DONE | Mask bit for corresponding bit in interrupt request register. |
| UART_ARB_LOST | Mask bit for corresponding bit in interrupt request register. |