За эти два дня можно было и эксперимент поставить.
Цитата из DS:
Цитата
The receiver detects a break condition when all data, parity and stop bits are low. This corresponds
to detecting a framing error with data at 0x00, but FRAME remains low.
When the low stop bit is detected, the receiver asserts the RXBRK bit in US_CSR. This bit may
be cleared by writing the Control Register (US_CR) with the bit RSTSTA at 1.
An end of receive break is detected by a high level for at least 2/16 of a bit period in asynchronous
operating mode or one sample at high level in synchronous operating mode. The end of
break detection also asserts the RXBRK bit.
Т.е. framing error'а Вы не получите, данные во время break приниматься не будут.