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13.5
Usage Notes
13.5.1
Notes on Use of SCI
Note the following points when using the SCI.
TDR Write and TDRE Flag: The TDRE flag in SSR is a status flag indicating the loading of
transmit data from TDR to TSR. The SCI sets the TDRE flag to 1 when it transfers data from TDR
to TSR.
Data can be written into TDR regardless of the state of the TDRE flag. If new data is written in
TDR when the TDRE flag is 0, the old data stored in TDR will be lost because this data has not
yet been transferred to TSR. Before writing transmit data in TDR, be sure to check that the TDRE
flag is set to 1.
Simultaneous Multiple Receive Errors: Table 13.13 shows the state of the SSR status flags
when multiple receive errors occur simultaneously. When an overrun error occurs the RSR
contents are not transferred to RDR, so receive data is lost.
Table 13.13 SSR Status Flags and Transfer of Receive Data
SSR Status Flags
RDRF
ORER
FER
1
1
0
0
0
1
0
0
0
1
1
1
1
1
0
0
0
1
1
1
1
Notes: ! : Receive data is transferred from RSR to RDR.
× : Receive data is not transferred from RSR to RDR.
Break Detection and Processing: Break signals can be detected by reading the RxD pin directly
when a framing error (FER) is detected. In the break state the input from the RxD pin consists of
all 0s, so the FER flag is set and the parity error flag (PER) may also be set. In the break state the
SCI receiver continues to operate, so if the FER flag is cleared to 0 it will be set to 1 again.
Receive Data Transfer
RSR → → → → RDR
PER
×
0
!
0
!
1
×
0
×
1
!
1
×
1
Section 13 Serial Communication Interface
Receive Errors
Overrun error
Framing error
Parity error
Overrun error + framing error
Overrun error + parity error
Framing error + parity error
Overrun error + framing error +
parity error
Rev. 4.00 Jan 26, 2006 page 535 of 938
REJ09B0276-0400
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