Transmitter interrupt masked request
| TRIGGER | Logical and of corresponding request and mask bits. |
| NOT_FULL | Logical and of corresponding request and mask bits. |
| EMPTY | Logical and of corresponding request and mask bits. |
| OVERFLOW | Logical and of corresponding request and mask bits. |
| UNDERFLOW | Logical and of corresponding request and mask bits. |
| BLOCKED | Logical and of corresponding request and mask bits. |
| UART_NACK | Logical and of corresponding request and mask bits. |
| UART_DONE | Logical and of corresponding request and mask bits. |
| UART_ARB_LOST | Logical and of corresponding request and mask bits. |