Datasheet

Section 12 Serial Communication Interface
Rev.7.00 Dec. 24, 2008 Page 410 of 698
REJ09B0074-0700
12.4.6 Serial Data Reception (Asynchronous Mode)
Figure 12.11 shows an example of operation for reception in asynchronous mode. In serial
reception, the SCI operates as described below.
1. The SCI monitors the communication line. If a start bit is detected, the SCI performs internal
synchronization, receives receive data in RSR, and checks the parity bit and stop bit.
2. If an overrun error occurs (when reception of the next data is completed while the RDRF flag
is still set to 1), the ORER bit in SSR is set to 1. If the RIE bit in SCR is set to 1 at this time, an
ERI interrupt request is generated. Receive data is not transferred to RDR. The RDRF flag
remains to be set to 1.
3. If a parity error is detected, the PER bit in SSR is set to 1 and receive data is transferred to
RDR. If the RIE bit in SCR is set to 1 at this time, an ERI interrupt request is generated.
4. If a framing error is detected (when the stop bit is 0), the FER bit in SSR is set to 1 and receive
data is transferred to RDR. If the RIE bit in SCR is set to 1 at this time, an ERI interrupt
request is generated.
5. 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 SCR is set to 1 at this time, an RXI interrupt request is
generated. Continuous reception is possible because the RXI interrupt routine reads the receive
data transferred to RDR before reception of the next receive data has been completed.
RDRF
FER
0
1 frame
D0 D1 D7 0/1 1 0 D0 D1 D7 0/1 0
1 1
DataStart
bit
Parity
bit
Stop
bit
Start
bit
Data Parity
bit
Stop
bit
ERI interrupt request
generated by framing
error
Idle state
(mark state)
RDR data read and RDRF
flag cleared to 0 in RXI
interrupt service routine
RXI interrupt
request
generated
Figure 12.11 Example of SCI Operation in Reception
(Example with 8-Bit Data, Parity, One Stop Bit)
Table 12.11 shows the states of the SSR status flags and receive data handling when a receive error
is detected. If a receive error is detected, the RDRF flag retains its state before receiving data.
Reception cannot be resumed while a receive error flag is set to 1. Accordingly, clear the ORER,
FER, PER, and RDRF bits to 0 before resuming reception. Figure 12.12 shows a sample flow chart
for serial data reception.