SH7708 Datasheet, PDF (383/625 Pages) Renesas Technology Corp – SuperH™ RISC engine

In receiving, the SCI operates as follows:
1. The SCI monitors the communication line. When it detects a start bit (0), the SCI
synchronizes internally and starts receiving.
2. Receive data is shifted into SCRSR in order from the LSB to the MSB.
3. The parity bit and stop bit are received. After receiving these bits, the SCI makes the following
checks:
a. Parity check: The number of 1s in the receive data must match the even or odd parity
setting of the O/E bit in SCSMR.
b. Stop bit check: The stop bit value must be 1. If there are two stop bits, only the first stop
bit is checked.
c. Status check: RDRF must be 0 so that receive data can be loaded from SCRSR into
SCRDR.
If these checks all pass, the SCI sets RDRF to 1 and stores the received data in SCRDR. If
one of the checks fails (receive error), the SCI operates as indicated in table 13.12.
Note: When a receive error flag is set, further receiving is disabled. The RDRF bit is not
set to 1. Be sure to clear the error flags.
4. After setting RDRF to 1, if the receive-data-full interrupt enable bit (RIE) is set to 1 in
SCSCR, the SCI requests a receive-data-full interrupt (RXI). If one of the error flags (ORER,
PER, or FER) is set to 1 and the receive-data-full interrupt enable bit (RIE) in SCSCR is also
set to 1, the SCI requests a receive-error interrupt (ERI).
Table 13.12 Receive Error Conditions and SCI Operation
Receive Error Abbreviation Condition
Data Transfer
Overrun error ORER
Receiving of next data ends while Receive data not loaded
RDRF is still set to 1 in SCSSR from SCRSR into SCRDR
Framing error FER
Stop bit is 0
Receive data loaded from
SCRSR into SCRDR
Parity error
PER
Parity of receive data differs from Receive data loaded from
even/odd parity setting in SCSMR SCRSR into SCRDR
Figure 13.8 shows an example of SCI receive operation in asynchronous mode.
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