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11.5 Usage Notes
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 into 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 11-13 indicates the state of 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 11-13 SSR Status Flags and Transfer of Receive Data
SSR Status Flags
Receive Data
Transfer
RDRF
ORER
FER
PER
RSR
→
RDR
Receive Errors
1
1
0
0
Not transferred
Overrun error
0
0
1
0
Transferred
Framing error
0
0
0
1
Transferred
Parity error
1
1
1
0
Not transferred
Overrun error + framing error
1
1
0
1
Not transferred
Overrun error + parity error
0
0
1
1
Transferred
Framing error + parity error
1
1
1
1
Not transferred
Overrun error + framing error + parity
error