When using SCI transmit with the DTC it seems that all the expected data is not transferred unless the DTC counter is set as transfer data + 1?
The DTC does not clear the flag after the the last data transfer. Since the TDRE bit is not cleared after SCI transmit end, byte transfer is not started. TXI interrupt occurs because TDRE bit is still set. It is possible to transmit end byte if TDRE is cleared.