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In serial reception, the SCI1 operates as described below.
[1] The SCI1 monitors the transmission line, and if a 0 stop bit is detected, performs internal
synchronization and starts reception.
[2] The received data is stored in RSR in LSB-to-MSB order.
[3] The parity bit and stop bit are received.
After receiving these bits, the SCI1 carries out the following checks.
[a] Parity check:
The SCI1 checks whether the number of 1 bits in the receive data agrees with the parity
(even or odd) set in the O/
[b] Stop bit check:
The SCI1 checks whether the stop bit is 1.
If there are two stop bits, only the first is checked.
[c] Status check:
The SCI1 checks whether the RDRF flag is 0, indicating that the receive data can be
transferred from RSR to RDR1.
If all the above checks are passed, the RDRF flag is set to 1, and the receive data is stored
in RDR1.
If a receive error* is detected in the error check, the operation is as shown in table 23.11.
Note: * Subsequent receive operations cannot be performed when a receive error has
occurred.
Also note that the RDRF flag is not set to 1 in reception, and so the error flags must
be cleared to 0.
[4] If the RIE bit in SCR1 is set to 1 when the RDRF flag changes to 1, a receive-data-full
interrupt (RXI) request is generated.
Also, if the RIE bit in SCR1 is set to 1 when the ORER, PER, or FER flag changes to 1, a
receive-error interrupt (ERI) request is generated.
Table 23.11 Receive Errors and Conditions for Occurrence
Receive Error
Abbrev.
Overrun error
ORER
Framing error
FER
Parity error
PER
bit in SMR1.
Occurrence Condition
When the next data reception is
completed while the RDRF flag
in SSR1 is set to 1
When the stop bit is 0
When the received data differs
from the parity (even or odd) set
in SMR1
Data Transfer
Receive data is not transferred
from RSR to RDR1
Receive data is transferred
from RSR to RDR1
Receive data is transferred
from RSR to RDR1
Rev. 2.0, 11/00, page 477 of 1037
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