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Rev. 1.0, 07/01, page 206 of 372
14.5.4 Serial Data Reception (Clocked Synchronous Mode)
Figure 14-12 shows an example of SCI operation for reception in clocked synchronous mode. In
serial reception, the SCI operates as described below.
1.
The SCI performs internal initialization synchronous with a synchronization clock input or
output, starts receiving data.
2.
The SCI stores the receive data in RSR.
3.
If an overrun error occurs (when reception of the next data is completed while the RDRF flag
in SSR is still set to 1), the OER bit in SSR is set to 1. If the RIE bit in SCR3 is set to 1 at this
time, an ERI interrupt request is generated, receive data is not transferred to RDR, and the
RDRF flag remains to be set to 1.
4.
If reception is completed successfully, the RDRF bit in SSR is set to 1, and receive data is
transferred to RDR. If the RIE bit in SCR3 is set to 1 at this time, an RXI interrupt request is
generated.
Reception cannot be resumed while a receive error flag is set to 1. Accordingly, clear the OER,
FER, PER, and RDRF bits to 0 before resuming reception. Figure 14-13 shows a sample flow
chart for serial data reception.
Synchronization
clock
Serial
data
1 frame 1 frame
Bit 0Bit 7 Bit 7 Bit 0 Bit 1 Bit 6 Bit 7
RDRF
OER
LSI
operation
User
processing
RXI interrupt request generated
RDR data read
RDRF flag
cleared
to 0
RXI interrupt
request
generated
ERI interrupt request
generated by
overrun error
Overrun error
processing
RDR data has
not been read
(RDRF = 1)
Figure 14-12 Example of SCI Reception in Clocked Synchronous Mode