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In serial reception, the SCI operates as described below.
[1] The SCI performs internal initialization in synchronization with serial clock input or output.
[2] The received data is stored in RSR in LSB-to-MSB order.
After reception, the SCI checks whether the RDRF flag is 0 and the receive data can be
transferred from RSR to RDR.
If this check is passed, the RDRF flag is set to 1, and the receive data is stored in RDR. If a
receive error is detected in the error check, the operation is as shown in table 16-11.
Neither transmit nor receive operations can be performed subsequently when a receive error
has been found in the error check.
[3] If the RIE bit in SCR 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 SCR is set to 1 when the ORER flag changes to 1, a receive error
interrupt (ERI) request is generated.
Figure 16-19 shows an example of SCI operation in reception.
Serial
clock
Serial
data
RDRF
ORER
RXI interrupt request
generated
• Simultaneous serial data transmission and reception (clocked synchronous mode)
Figure 16-20 shows a sample flowchart for simultaneous serial transmit and receive operations.
The following procedure should be used for simultaneous serial data transmit and receive
operations.
Bit 7
Bit 0
RDR data read and
RDRF flag cleared to 0
in RXI interrupt service
routine
1 frame
Figure 16-19 Example of SCI Operation in Reception
Bit 7
Bit 0
Bit 1
RXI interrupt request
generated
Bit 6
Bit 7
ERI interrupt request
generated by overrun
error
643
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