Datasheet

348
32133D–11/2011
UC3D
Figure 20-12. Framing Error Status
20.6.3.10 Transmit Break
When TXRDY is set, the user can request the transmitter to generate a break condition on the
TXD line by writing a one to The Start Break bit (CR.STTBRK). The break is treated as a normal
0x00 character transmission, clearing TXRDY and TXEMPTY, but with zeroes for preambles,
start, parity, stop, and time guard bits. Writing a one to the Stop Break bit (CR.STBRK) will stop
the generation of new break characters, and send ones for TG duration or at least 12 bit periods,
ensuring that the receiver detects end of break, before resuming normal operation. Figure 20-13
illustrates STTBRK and STPBRK effect on the TXD line.
Writing to STTBRK and STPBRK simultaneously can lead to unpredictable results. Writes to
THR before a pending break has started will be ignored.
Figure 20-13. Break Transmission
20.6.3.11 Receive Break
A break condition is assumed when incoming data, parity, and stop bits are zero. This corre-
sponds to a framing error, but FRAME will remain zero while the Break Received/End Of Break
bit (CSR.RXBRK) is set. Writing a one to CR.RSTSTA will clear RXBRK. An end of break will
also set RXBRK, and is assumed when TX is high for at least 2/16 of a bit period in asynchro-
nous mode, or when a high level is sampled in synchronous mode.
D0 D1 D2 D3 D4 D5 D6 D7
RXD
Start
Bit
Parity
Bit
Stop
Bit
Baud Rate
Clock
Write
CR
FRAME
RXRDY
RSTSTA = 1
D0 D1 D2 D3 D4 D5 D6 D7
TXD
Start
Bit
Parity
Bit
Stop
Bit
Baud Rate
Clock
Write
CR
TXRDY
TXEMPTY
STPBRK = 1
STTBRK = 1
Break Transmission End of Break