Renesas H8S Series Hardware Manual page 543

Break Detection and Processing (Asynchronous Mode Only): When framing error (FER) 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, and so
the FER flag is set, and the parity error flag (PER) may also be set.
Note that, since 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.
Sending a Break (Asynchronous Mode Only): The TxD pin has a dual function as an I/O port whose direction (input or
output) is determined by DR and DDR. This can be used to send a break.
Between serial transmission initialization and setting of the TE bit to 1, the mark state is replaced by the value of DR (the
pin does not function as the TxD pin until the TE bit is set to 1). Consequently, DDR and DR for the port corresponding to
the TxD pin are first set to 1.
To send a break during serial transmission, first clear DR to 0, then clear the TE bit to 0.
When the TE bit 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.
Receive Error Flags and Transmit Operations (Clocked Synchronous Mode Only):
Transmission cannot be started when a receive error flag (ORER, 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.
Receive Data Sampling Timing and Reception Margin in Asynchronous Mode:
In asynchronous mode, the SCI operates on a basic clock with a frequency of 16 times the transfer rate.
In reception, the SCI samples the falling edge of the start bit using the basic clock, and performs internal synchronization.
Receive data is latched internally at the rising edge of the 8th pulse of the basic clock. This is illustrated in figure 14-21.
Internal basic
clock
Receive data
(RxD)
Synchronization
sampling timing
Data sampling
timing
Thus the reception margin in asynchronous mode is given by formula (1) below.
1
M = | (0.5 –
2N
16 clocks
8 clocks
0 7
Start bit
Figure 14-21 Receive Data Sampling Timing in Asynchronous Mode
| D – 0.5 |
) – (L – 0.5) F –
15 0
(1 + F) | × 100%
N
7
D0
Rev.6.00 Oct.28.2004 page 515 of 1016
15 0
D1
... Formula (1)
REJ09B0138-0600H