In receiving, the SCI operates as follows.
•
The SCI monitors the receive data line. When it detects a start bit, the SCI synchronizes
internally and starts receiving.
•
Receive data is stored in RSR in order from LSB to MSB.
•
The parity bit and stop bit are received.
After receiving, the SCI makes the following checks:
— 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.
— Stop bit check: The stop bit value must be 1. If there are two stop bits, only the first stop
bit is checked.
— Status check:
The RDRF flag must be 0 so that receive data can be transferred from
RSR into RDR.
If these checks all pass, the RDRF flag is set to 1 and the received data is stored in RDR. If one of
the checks fails (receive error), the SCI operates as indicated in table 13-11.
Note: When a receive error occurs, further receiving is disabled. In receiving, the RDRF flag is
not set to 1. Be sure to clear the error flags to 0.
•
When the RDRF flag is set to 1, if the RIE bit is set to 1 in SCR, a receive-data-full interrupt
(RXI) is requested. If the ORER, PER, or FER flag is set to 1 and the RIE bit in SCR is also
set to 1, a receive-error interrupt (ERI) is requested.
Table 13-11 Receive Error Conditions
Receive Error
Abbreviation
Condition
Data Transfer
Overrun error
ORER
Receiving of next data ends
Receive data not transferred
while RDRF flag is still set to
from RSR to RDR
1 in SSR
Framing error
FER
Stop bit is 0
Receive data transferred
from RSR to RDR
Parity error
PER
Parity of receive data differs
Receive data transferred
from even/odd parity setting
from RSR to RDR
in SMR
474
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