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Rev. 1.0, 07/01, page 218 of 372
14.8 Usage Notes
14.8.1 Break Detection and Processing
When framing error detection is performed, a break can be detected by reading the RxD pin value
directly. In a break, the input from the RxD pin becomes all 0s, setting the FER flag, and possibly
the PER flag. Note that as the SCI continues the receive operation after receiving a break, even if
the FER flag is cleared to 0, it will be set to 1 again.
14.8.2 Mark State and Break Detection
When TE is 0, the TxD pin is used as an I/O port whose direction (input or output) and level are
determined by PCR and PDR. This can be used to set the TxD pin to mark state (high level) or
send a break during serial data transmission. To maintain the communication line at mark state
until TE is set to 1, set both PCR and PDR to 1. As TE is cleared to 0 at this point, the TxD pin
becomes an I/O port, and 1 is output from the TxD pin. To send a break during serial transmission,
first set PCR to 1 and clear PDR to 0, and then clear TE to 0. When TE is cleared to 0, the
transmitter is initialized regardless of the current transmission state, the TxD pin becomes an I/O
port, and 0 is output from the TxD pin.
14.8.3 Receive Error Flags and Transmit Operations (Clocked Synchronous Mode Only)
Transmission cannot be started when a receive error flag (OER, PER, or FER) is set to 1, even if
the TDRE flag is cleared to 0. Be sure to clear the receive error flags to 0 before starting
transmission. Note also that receive error flags cannot be cleared to 0 even if the RE bit is cleared
to 0.