384
In receiving, the SCI operates as follows:
1. The SCI monitors the receive data line. When it detects a start bit (0), the SCI synchronizes
internally and starts receiving.
2. Receive data is shifted into RSR 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 SMR.
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 RSR into RDR.
If these checks all pass, the SCI sets RDRF to 1 and stores the received data in RDR. If one of
the checks fails (receive error), the SCI operates as indicated in table 13.11.
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 SCR,
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 SCR is also set to 1, the
SCI requests a receive-error interrupt (ERI).
Figure 13.8 shows an example of SCI receive operation in asynchronous mode.
Table 13.11 Receive Error Conditions and SCI Operation
Receive Error Abbreviation Condition Data Transfer
Overrun error ORER Receiving of next data ends while
RDRF is still set to 1 in SSR
Receive data not loaded
from RSR into RDR
Framing error FER Stop bit is 0 Receive data loaded from
RSR into RDR
Parity error PER Parity of receive data differs from
even/odd parity setting in SMR
Receive data loaded from
RSR into RDR
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