47.7.3.14 Receive Break
The receiver detects a break condition when all data, parity and stop bits are low. This corresponds to detecting a framing error with data to 0x00, but FRAME remains low.
When the low stop bit is detected, the receiver asserts the FLEX_US_CSR.RXBRK bit. FLEX_US_CSR.RXBRK may be cleared by setting the FLEX_US_CR.RSTSTA bit.
An end of receive break is detected by a high level for at least 2/16ths 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.