34.2.1.5 TSR Status

The TXMTIF bit indicates the status of the TSR. This is a read-only bit. The TXMTIF bit is set when the TSR is empty and Idle. The TXMTIF bit is cleared when a character is transferred to the TSR from the UxTXB. The TXMTIF bit remains clear until all bits, including the Stop bits, have been shifted out of the TSR and a byte is not waiting in the UxTXB register.

The TXMTIF will generate a summary UxEIF interrupt when the TXMTIE bit is set.